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diff --git a/old/67569-0.txt b/old/67569-0.txt deleted file mode 100644 index ad85083..0000000 --- a/old/67569-0.txt +++ /dev/null @@ -1,4526 +0,0 @@ -The Project Gutenberg eBook of Tractor Principles, by Roger B. -Whitman - -This eBook is for the use of anyone anywhere in the United States and -most other parts of the world at no cost and with almost no restrictions -whatsoever. You may copy it, give it away or re-use it under the terms -of the Project Gutenberg License included with this eBook or online at -www.gutenberg.org. If you are not located in the United States, you -will have to check the laws of the country where you are located before -using this eBook. - -Title: Tractor Principles - -Author: Roger B. Whitman - -Release Date: March 5, 2022 [eBook #67569] - -Language: English - -Produced by: deaurider and the Online Distributed Proofreading Team at - https://www.pgdp.net (This file was produced from images - generously made available by The Internet Archive) - -*** START OF THE PROJECT GUTENBERG EBOOK TRACTOR PRINCIPLES *** - - - - - -Transcriber’s Notes: - - Underscores “_” before and after a word or phrase indicate _italics_ - in the original text. - Equal signs “=” before and after a word or phrase indicate =bold= - in the original text. - Small capitals have been converted to SOLID capitals. - Illustrations have been moved so they do not break up paragraphs. - Typographical and punctuation errors have been silently corrected. - - - - - TRACTOR PRINCIPLES - - THE ACTION, MECHANISM, HANDLING, - CARE, MAINTENANCE AND REPAIR - OF THE GAS ENGINE TRACTOR - - BY - ROGER B. WHITMAN - - AUTHOR OF - “MOTOR CAR PRINCIPLES,” - “GAS ENGINE PRINCIPLES,” - “MOTOR-CYCLE PRINCIPLES,” - ETC. - - [Illustration] - - FULLY ILLUSTRATED - - D. APPLETON AND COMPANY - NEW YORK LONDON - 1920 - - COPYRIGHT, 1920, - BY - D. APPLETON AND COMPANY - - PRINTED IN THE UNITED STATES OF AMERICA - - - - -FOREWORD - - -The tractor of to-day is built in almost as many types and designs -as there are tractor makers, and is far from being as standard as -the automobile. There are tractors with one driving wheel, with two -driving wheels, with three and with four, as well as three arrangements -of the crawler principle; there are two-wheelers, three-wheelers and -four-wheelers; tractors that are controlled by pedals and levers and -tractors that are driven by reins. - -Thus if a man who is competent to handle and care for one make is given -another make to run, he may be entirely at a loss as to how it works -and how it should be handled. - -It is the purpose of this book to explain and describe all of the -mechanisms that are in common use in tractor construction, to the end -that the reader may be able to identify and understand the parts of -whatever make he may see or handle. - - - - -CONTENTS - - - PAGE - CHAPTER I - TRACTOR PRINCIPLES - Comparison between tractors and automobiles—What is - required for each—Advantage of understanding the - mechanism—No standard tractor design—Principal - parts of a tractor—Necessity for each 1 - - CHAPTER II - ENGINE PRINCIPLES - Power attained from heat—Combustible mixture—Principle - of engine operation—Combustion space—Gas engine - cycle—Dead strokes—Flywheel—Starting an - engine—Inlet stroke—Compression stroke—Importance - of compression—Ignition—Advance and retard of - ignition—Power stroke—Exhaust stroke—Production of - power—Vertical and horizontal engines—Firing order 9 - - CHAPTER III - ENGINE PARTS - Base—Bearings—Cylinders—Crankshaft—Piston—Connecting - rod—Wrist pin—Piston rings—Valves—Cam—Valve - mechanisms—Cooling system 30 - - CHAPTER IV - FUELS AND CARBURETION - Oxygen necessary for combustion—Forming a mixture—Rich and - poor mixtures—Carbon—Preignition— Carbureter—Spray - nozzle—Evaporation of fuels—Carbureter principles— - Extra air inlet—Effect of heat on mixture—Loading— - Strangler 52 - - CHAPTER V - CARBURETERS - Carbureter parts—Manifold—Action of carbureter—Float - feed—Kerosene and gasoline—Descriptions of - carbureters—Pump feed—Use of water in the - mixture—Application of heat—Fuel pumps—Air - cleaners—Governors 70 - - CHAPTER VI - IGNITION - Principle of ignition—Point of - ignition—Preignition—Advance and retard—Parts of - ignition system—Magnetism—Induction—Magneto—Action - of armature—Armature windings—Circuit - breaker—Circuit—Shuttle and inductor - armatures—Sparking current—Grounded circuit— - Magneto parts—Impulse starter 102 - - CHAPTER VII - BATTERY IGNITION SYSTEMS - Principle of spark coil—Windings—Timer—Atwater-Kent - system—Vibrator—Spark plugs 131 - - CHAPTER VIII - TRANSMISSION - Transmission parts—Clutches—Necessity for change speed - gear—High and low gear—Types of change speed - gears—Necessity for differential—Principle of - differential—Drives—Worm 143 - - CHAPTER IX - TRACTOR ARRANGEMENT - Tractor requirements—Tractor types—Engine position— - Front axles—Spring supports 167 - - CHAPTER X - LUBRICATION - Importance of lubrication—Effect of oil—Kinds of - oil—Effect of temperature on oil—Using the right - kind of oil—Burning point—Viscosity—Lubrication - charts—Oiling systems—Oil pumps—Mechanical oiler— - Oil cup—Grease cup 175 - - CHAPTER XI - TRACTOR OPERATION - Using a new tractor—Breaking in—Daily - inspection—Driving—Shifting gears—Driving on - hills—Using the engine as a brake—Cold weather - conditions—Starting in cold weather—Protection - against freezing—Starting a tractor 201 - - CHAPTER XII - ENGINE MAINTENANCE - Fuel system and carbureter—Carbureter adjustment—Dirt - in the fuel—Running on kerosene—Care—Magneto and - ignition system—Care of magneto—Smoothing platinum - points—Adjustment—Timing a magneto—Testing a - magneto—Ignition trouble—Compression—Testing - for compression leaks—Valve grinding—Valve - timing—Carbon—Removing carbon 213 - - CHAPTER XIII - LOCATING TROUBLE - Engine will not start—Engine loses power—Engine - stops—Engine misses—Engine starts; but stops—Engine - overheats—Engine smokes 245 - - CHAPTER XIV - CAUSES OF TROUBLE - Troubles and their causes in tabular form 259 - - INDEX 261 - - - - -ILLUSTRATIONS - - - FIG. PAGE - 1 The Gas Engine Cycle 15 - 2 1-cylinder power diagram 21 - 3 2-cylinder power diagram 22 - 4 2-cylinder power diagram, 180 shaft 24 - 5 H. D. O. power diagram 26 - 6 4-cylinder power diagram 27 - 7 2-cylinder crank shaft 31 - 8 4-cylinder crank shaft 32 - 9 Half of a plain bearing 32 - 10 Connecting rod bearings 33 - 11 Piston complete and in section 34 - 12 Wrist pin fastenings 36 - 13 Valve 38 - 14 Action of cam 39 - 15 “Twin City” tractor engine 41 - 16 “Hart-Parr” valve mechanism 43 - 17 “Hart-Parr” engine 45 - 18 “Oil-Pull” engine 47 - 19 Horizontal double opposed engine 49 - 20 “Monarch” engine 51 - 21 Principle of carburetor 59 - 22 Principle of extra air inlet 64 - 23 “Kingston” carburetor, model L 72 - 24 “Kingston” carburetor, model E 75 - 25 “Kingston” carburetor, dual model 77 - 26 “E-B” carburetor 79 - 27 “E-B” carburetor, side view 81 - 28 Pump-fed carburetor 82 - 29 “Titan” carburetor 84 - 30 Pump-fed carburetor with two fuel nozzles 85 - 31 “Hart-Parr” mixture heater 87 - 32 “Twin City” manifold 88 - 33 Fuel pump 90 - 34 “Avery” fuel connections 92 - 35 “Oil-Pull” fuel system 93 - 36 Air washer 95 - 37 Air strainer 96 - 38 “E-B” governor 97 - 39 “Case” governor 98 - 40 “Hart-Parr” governor 99 - 41 Vertical governor 101 - 42 Armature 107 - 43 Flow of magnetism through armature core 108 - 44 One complete revolution of the armature 111 - 45 Connections of Bosch magneto 112 - 46 “K-W” inductor 115 - 47 “K-W” inductor in three positions 117 - 48 “Dixie” inductor 118 - 49 Three positions of “Dixie” inductor 120 - 50 “Bosch” circuit breaker 121 - 51 “K-W” circuit breaker 122 - 52 “Bosch” magneto in section 126 - 53 “K-W” magneto in section 129 - 54 Magnetism in a copper wire 132 - 55 Magnetism from electricity 133 - 56 Principle of spark coil 134 - 57 “Atwater-Kent” ignition system 136 - 58 Vibrator coil ignition system 139 - 59 Spark plug 141 - 60 Internal clutch 144 - 61 Plate clutch 147 - 62 Principle of sliding gear 155 - 63 Principle of jaw clutch change speed gear 157 - 64 “I. H. C.” chain drive, showing differential 162 - 65 “Case” rear axle 163 - 66 “Oil-Pull” rear axle 164 - 67 Driving worm 165 - 68 Tractor arrangement 168 - 69 Tractor arrangement 169 - 70 “Gray” tractor 171 - 71 Types of front axles 172 - 72 Spring support 173 - 73 “Mogul” oiling diagram 180 - 74 “Illinois” oiling diagram 183 - 75 End of “Twin City” connecting rod 185 - 76 Wrist pin lubrication 186 - 77 Force feed oiling system of “Gray” engine 187 - 78 Oil pump 188 - 79 “E-B” oil pump 189 - 80 Oil pump with hollow plunger 190 - 81 Methods of preventing oil leaks 191 - 82 “Titan” lubricator 192 - 83 “I. H. C.” method of oiling crank pins 193 - 84 “Hart-Parr” oiling system 194 - 85 Oil cup 195 - 86 Proper use of a grease cup 196 - 87 “Titan” 10-20 oiling diagram 198 - 88 “International” oiling diagram 199 - 89 Grinding valve in engine with fixed head 231 - 90 Grinding valve in detachable head 233 - 91 Grinding valve in detachable seat 234 - 92 Valve seat cutter 235 - 93 “Holt” valve arrangement 236 - 94 Valve timing, using marks on flywheel 238 - 95 Valve timing 239 - - - - -TRACTOR PRINCIPLES - - - - -CHAPTER I - -TRACTOR PRINCIPLES - - -While tractors and automobiles are the same in general principles, -there is a wide difference between them in design, construction, and -handling, due to the differences in the work that they do and in the -conditions under which they do it. - -An automobile is required to move only itself and the load that it -carries. While it can run over rough roads, these must be hard enough -to support it; on soft ground it will sink in and be unable to get -itself out. It can make great speed over smooth, level roads; but only -rarely do road and police conditions permit it to run its fastest for -more than a few minutes at a time. For the greater part of its life it -develops only a portion of the power of which it is capable. - -A tractor, on the other hand, is intended not to carry, but to haul. -It must run and do its work on rough hillsides, soft bottoms, or any -other land where it is required to go. Instead of developing speed it -develops pulling power, and must be able to develop its full power -continuously. - -Appearance and comfort count for a great deal in an automobile, and -much attention is devoted to making it noiseless and simple to manage. -These things do not apply in a tractor, which is a labor-saving and -money-making machine, valuable only for the work that it can do. There -is no question of upholstery or nickel-plating; all that is wanted is a -machine that will do the required work with the least possible cost of -operation. - -As is the case with any kind of machine that is purchased as a -money-maker, its cost should be as low as is consistent with its -ability to do its work. Any extra cost for accessories, or finish, or -other detail, is wasted unless it permits the machine to do more work, -or, by making the operator more comfortable, allows him to run the -machine for a longer stretch of time or with greater efficiency. - -It may be taken for granted that any tractor will run and will do its -work with satisfaction, provided it is sensibly handled and cared for. -Far more troubles and breakdowns come from careless handling and from -neglect than from faulty design and material. A tractor that is running -and doing its work is earning a return on the money invested in it; -when it is laid up for repairs there is not only a loss of interest on -the investment, but a loss of the value of the work that it might be -doing. - -To keep a tractor running is a matter only of understanding and of -common sense; common sense to realize that any piece of machinery needs -some degree of care and attention, and understanding of where the care -and attention should be applied. The more thoroughly a tractor operator -understands his machine, the more work he will be able to get out of -it, and the more continuously it will run. This is only another way of -saying that understanding and knowledge pay a direct return in work -done and money earned. - -In the early days of the automobile there were as many types of cars -as there were manufacturers. As time has gone on, the unsatisfactory -ideas have been weeded out, and automobiles have approached what may be -called a standard design. - -At the present time, tractor designs are varied, and it is hardly -possible to speak of any type as standard. The reason for this lies in -the fact that many manufacturers start with a design for one special -part, and build the tractor around it. - -For example, a manufacturer may develop a method of driving the wheels -that he feels is especially good for tractor work. In applying it he -may find that the engine must be so placed on the frame that when the -power pulley is in position the belt will interfere with the front -wheels unless they are small; he therefore uses small front wheels, and -advocates them for tractors. - -Another manufacturer with a patent steering gear may be able to place -the power pulley so that there is ample clearance for the belt; he -finds that by using high front wheels he can get a better support for -the frame, and therefore claims that high front wheels are an advantage. - -Other designs may be based on having three wheels, or two; advantages -are claimed for each type, and each type undoubtedly has them. - -The selection of a tractor is based on one’s own experience or on -that of neighbors, or on the ability of the salesman to bring out the -advantages of the make that he sells; but when the tractor is bought -and delivered, its ability to do the work promised for it depends -solely on the care with which it is handled and looked after. - -Whatever the design of a tractor may be, there are certain parts that -it must have in order to do the work required of it. These parts, or -groups of parts, are as follows: - -=Engine.=—This furnishes the power by which the tractor operates. - -=Clutch.=—By means of a clutch the engine may be connected with the -mechanism, so that the tractor moves, or it may be disconnected, so -that it may run without moving the tractor. - -=Change Speed Gear.=—As will be explained in later chapters, an engine, -in order to work most efficiently, should run at a fixed speed; the -tractor should be able to run fast or slow, according to conditions. -A change speed gear is therefore provided, by which the speed of the -tractor may be changed, although there is no change in the speed of the -engine. - -=Drive.=—The drive is the mechanism that applies the power of the -engine to the wheels, and makes them turn. - -=Differential.=—When a tractor makes a turn, the outside wheels cover -a larger circle than the inside wheels, and therefore must run faster -in order to get around in the same time. It is usually the case that -the power of the engine is applied to both driving wheels; if both were -solid on the axle, like the wheels of a railroad car, one would be -forced to slip when making a turn, which would waste power. By applying -a differential, the engine can drive both wheels, but the wheels may -run at different speeds when conditions require it. - -The clutch, change speed gear, drive and differential form the -_transmission_. - -=Steering gear.=—By means of the steering gear the direction in which -the tractor moves may be changed. - -=Supports.=—A tractor moves on broad-tired wheels, or on crawlers, -which are so formed that they grip the ground and do not slip. They -give so broad a support that even on soft ground the weight of the -tractor will not pack the soil sufficiently to injure it as a seed bed. - -=Frame.=—The frame is the foundation of the tractor, and holds the -parts in the proper relation to each other. It is usually made of -channel steel, the parts being bolted to it; in some tractors, however, -the parts are so attached to each other that they form their own -support, and no other frame is needed. - -Tractor manufacturers make these parts in different ways; all -accomplish the same result, but do it by different methods. The main -principles are much the same, and should be known and understood. They -are described and explained in the succeeding chapters. - - - - -CHAPTER II - -ENGINE PRINCIPLES - - -The working part of a tractor is the engine; it is this that furnishes -the power that makes the machine go. - -The engine gets its power from the burning of a mixture of fuel vapor -and air. When this mixture burns, it becomes heated, and, as is usual -with hot things, it tries to expand, or to occupy more room. - -The mixture is placed in a cylinder, between the closed end and the -piston; it is then heated by being burned, and, in struggling to -expand, it forces the piston to slide down the cylinder. This movement -of the piston makes the crank shaft revolve, which in turn drives the -tractor. - -The first step in making the engine run is to put a charge of mixture -into the cylinder, and it is clear that if the burning of the charge is -to move the piston, the piston must be in such a position that it is -able to move. When the mixture is burned, the piston must therefore be -at the closed end of the cylinder. - -After the charge of mixture has been burned, the cylinder must be -cleared of the dead and useless gases that remain, in order to make -room for a fresh charge. - -The charge of mixture is drawn into the cylinder just as a pump sucks -in water. At a time when the piston is at the closed end of the -cylinder, a valve is opened connecting the space above the piston with -the device that forms the mixture; then by moving the piston outward, -mixture is sucked into the space above it. When the piston reaches the -end of its stroke the cylinder has been filled with mixture, and the -valve then closes. - -It would be useless to set fire to the mixture at that time, for the -piston is as far down the cylinder as it can be, and pressure could -not move it any farther. To get the piston into such a position that -the expanding mixture can move it, it is forced back to the closed end -of the cylinder. This squeezes or _compresses_, the cylinderful of -mixture into the small space, called the _combustion chamber_, between -the piston and the cylinder head. - -If the mixture is now burned, the piston can move the length of the -cylinder, and in so doing it develops power. - -The cylinder is cleared of the burned and useless gases by opening a -valve and pushing them out by moving the piston back to the inner end -of the cylinder. When this has been done, the valve is closed, and, by -opening the inlet valve and moving the piston outward, a fresh charge -is sucked in, and the several steps of the _gas engine cycle_ are -repeated. - -The name _cycle_ is given to any series of steps or events that must be -gone through in order that a thing may happen. Thus the empty shell -must be taken out of a gun and a fresh cartridge put in before the gun -can be fired again, and that series of steps might be called the gun -cycle. - -The gas engine cycle requires the piston to make four strokes. An -outward stroke sucks in a charge of mixture, and an inward stroke -returns the piston to the firing position and compresses the charge. -Then comes the outward stroke when the piston moves under power, -followed by the inward stroke that clears the cylinder of the burned -gases. - -For every stroke of the piston the crank shaft makes a half-revolution; -the crank shaft therefore makes two revolutions to four strokes of the -piston and to each repetition of the gas engine cycle. - -Of these four strokes of the piston only one produces power. The other -three strokes, called the _dead strokes_, are required to prepare for -another power stroke. - -A gas engine cylinder thus produces power for only one quarter of the -time that it runs. This is one of the striking differences between the -gas engine and the steam engine, for the piston of a steam engine moves -under power all of the time that the engine runs. - -A one-cylinder gas engine must have something to make the piston go -through the dead strokes, for otherwise the piston would stop at -the end of the power stroke; the piston is kept in motion by heavy -flywheels attached to the crank shaft. These, like any object, try to -continue in motion when once they are started; a power stroke starts -the crank shaft revolving and its flywheels keep it going. - -Thus, the piston drives the crank shaft during the power stroke, and -the crank shaft drives the piston during the dead strokes. - -To start an engine, the crank shaft is revolved to make the piston suck -in a charge of mixture and compress it; then the charge is burned, the -power stroke takes place, and the engine runs. - -A clear idea of what goes on inside of the cylinder is quite necessary -in order to take proper care of an engine and to get the best work -out of it. The following description applies to any cylinder, for the -action in all cylinders of an engine is the same. - -=Inlet Stroke.=—During the inlet stroke (No. 1, Fig. 1), the piston -moves outward; the inlet valve is open, and the exhaust valve is -closed. This movement of the piston creates suction, and if there -are leaks in the cylinder, air will be sucked in and will spoil the -proportions of the charge. This will prevent the proper burning of the -mixture, and the engine will lose power. - -The piston moves at such high speed that the mixture cannot enter fast -enough to keep up with it; mixture is still flowing in when the piston -reaches the end of its stroke, and even when it begins to move inward -on the next stroke. The more mixture there is in the cylinder, the more -powerfully the engine will run; the inlet valve is therefore held open -for as long a time as the mixture continues to enter. - -[Illustration] - -[Illustration: FIG. 1.—THE GAS ENGINE CYCLE] - -In slow-speed 1-cylinder and 2-cylinder engines the valve closes when -the piston reaches the end of its stroke; on high-speed engines the -valve does not close until the piston has moved ¼ inch or ½ inch on the -compression stroke. - -=Compression Stroke.=—During the compression stroke (No. 2, Fig. 1) -the piston moves inward, and both valves are closed. This movement -places the piston in position to move outward on the power stroke. -As the outlets to the cylinder are closed, the charge of mixture -cannot escape, and is therefore compressed into the space between the -piston and the cylinder head when the piston is at the inner end of -its stroke. This space is usually about one quarter the volume of the -cylinder; the charge is therefore compressed to about one quarter of -its original volume. - -This compression of the charge is very important in the operation of -the gas engine, and any interference with it will make the engine run -poorly. - -In the first place, it improves the quality of the charge, and makes it -burn very much better. When the charge enters the cylinder, the fuel -vapor and air are not thoroughly mixed; much of the fuel is not turned -into vapor. By compressing the charge it becomes heated; this vaporizes -the fuel, and vapor and air become thoroughly mixed. - -Compression also increases the power. Suppose that the cylinder -contains a quart of mixture which, when heated, will expand to a -gallon. If this quart of mixture is compressed to a half pint, it -will not lose its ability to expand to a gallon, and will exert more -pressure in expanding from a half pint to a gallon than from a quart to -a gallon. - -A leaky cylinder will cause a further loss of power because some of the -charge will escape during the compression stroke, which will leave less -to be burned and to develop power. - -=Ignition.=—Setting fire to the charge of mixture is called the -_ignition_ of the charge, and it takes place close to the end of the -compression stroke. To get the greatest power, all of the mixture -should be on fire and heated most intensely as the piston begins the -power stroke. - -When the mixture is set on fire, it does not explode like gunpowder, -but burns comparatively slowly; the charge is ignited by an electric -spark, and the flame spreads from that point until it is all on -fire. In order to give the flame time to spread, the spark passes -sufficiently before the end of the compression stroke to have the -entire charge on fire as the power stroke begins. This is called the -_advance_ of the ignition. - -The flame takes the same time to spread through the charge when the -engine is running fast as when it is running slow. Therefore if the -engine is speeded up, the spark must be advanced, for otherwise the -piston would be on the power stroke before the flame would have time to -spread all through the mixture. - -When the engine is slowed down, the spark must have less advance, or -must be _retarded_, for, if it were not, the charge would all be in -flame, and exerting its full pressure, before the piston reached the -end of its compression stroke. - -The subject of ignition, which is of great importance, is covered more -fully in Chapter VI. - -=Power Stroke.=—During the power stroke (No. 3, Fig. 1) the piston -moves outward, and both valves are closed. As it begins, the mixture is -all on fire, and great pressure is exerted against the piston. - -As the piston moves outward the combustion space becomes larger, and -the gases obtain the room for expansion that they seek. As they expand, -the pressure that they exert becomes less. By the time the piston -is three quarters the way down the power stroke, the pressure is so -reduced that it has little or no effect; the gases are still trying to -expand, however, so the exhaust valve is opened at that point, and they -begin to escape. - -=Exhaust Stroke.=—During the exhaust stroke (No. 4, Fig. 1) the piston -moves inward and the exhaust valve is open. This movement of the piston -pushes the burned gases out of the cylinder, and it is clear that the -more thoroughly the cylinder is emptied of them, the more room there -will be for a fresh charge. - -In high-speed engines the gases cannot escape as fast as the piston -moves; they are still flowing out when the end of the stroke is -reached. Therefore the valve is closed, not at the end of the stroke, -but when the piston has moved about ⅛ inch outward on the inlet stroke. -The inlet valve opens as the exhaust valve closes. - -It can be seen that through the inlet and compression strokes a leak -will reduce the charge and so interfere with the production of full -power. The piston must make a tight fit in the cylinder, the valves -must seat tightly, and gaskets and other parts must be in proper -condition. - -[Illustration: FIG. 2.—1-CYLINDER POWER DIAGRAM] - -Figure 2 shows a power diagram for a 1-cylinder engine, in which the -crank shaft moves under power during one stroke out of every four. An -engine with two cylinders can be built so that first one cylinder -applies power and then the other, in which case the crank shaft moves -under power during two strokes out of every four. - -[Illustration: FIG. 3.—2-CYLINDER POWER DIAGRAM] - -Figure 3 is a power diagram of an engine of this sort. If piston 1 is -moving down under power, piston 2 is also moving down, but on the inlet -stroke. The following stroke is exhaust in cylinder 1 and compression -in cylinder 2, and cylinder 2 will then deliver a power stroke while -cylinder 1 is on inlet. Thus the crank shaft will receive a power -stroke, followed by a dead stroke; then another power stroke and -another dead stroke, and so on. - -There will be the disadvantage, however, that the pistons, moving up -and down together, will cause vibration, which in the course of time -will be likely to give trouble. To overcome this, a 2-cylinder engine -can be built as indicated in Figure 4. - -In this engine the cranks project on opposite sides of the crank shaft -instead of on the same side, as in Figure 3; the pistons thus move in -opposite directions, and produce no vibration. Power will be unevenly -applied, however, for both power strokes occur in one revolution, with -two dead strokes in the succeeding revolution. - -[Illustration] - -[Illustration: FIG. 4.—2-CYLINDER POWER DIAGRAM, 180 SHAFT] - -With piston 1 moving down on power, piston 2, moving upward, can only -be performing compression or exhaust. If it is on compression, its -power stroke will follow the power stroke of piston 1, while if it is -on exhaust its power stroke will have occurred immediately before the -power stroke of piston 1. In either case one power stroke follows the -other, taking place in one revolution of the crank shaft, while in the -following revolution both pistons will be performing dead strokes. - -While there is no vibration from the movement of the pistons in this -engine, the uneven production of power will produce vibration of -another kind. - -These two types may be built with the cylinders standing up or lying -down; that is, they may be either _vertical engines_ or _horizontal -engines_. The _double opposed_ engine, which is built only in horizontal -form, is free from either kind of vibration, but has the disadvantage -of occupying more room than the others. The cylinders, instead of being -side by side, and on the same side of the crank shaft, are placed end -to end, with the crank shaft between them, as shown in Figure 5. - -The pistons make their inward and outward strokes together, but in so -doing they move in opposite directions. Thus every power stroke is -followed by a dead stroke, as in the engine shown in Figure 3, while -the movement of one piston balances that of the other, as is the case -with the engine shown in Figure 4. - -[Illustration: FIG. 5.—H. D. O. POWER DIAGRAM] - -[Illustration] - -[Illustration: FIG. 6.—4-CYLINDER POWER DIAGRAM] - -In a 4-cylinder engine one power stroke follows another without any -dead stroke intervals, which, of course, makes the crank shaft revolve -more smoothly and with a steadier application of power. The power -diagram is shown in Figure 6; in studying this it should be remembered -that if two pistons move in opposite directions, as in Figure 4, -one power stroke follows another, while if they move in the same -direction, as in Figure 3, there is an interval of one stroke between -their power strokes. - -The crank shaft of a 4-cylinder engine is so made that the middle -pistons move in the same direction, and opposite to the end pistons. -This construction has been found to make a smoother running engine than -if pistons 1 and 3 moved one way while pistons 2 and 4 moved the other. - -If piston 1 is on the power stroke, either piston 2 or piston 3 can -follow, for they are moving in the opposite direction. If we say that -piston 2 is the next, then piston 4 must be the third to give a power -stroke, for it is the only one left that is moving in the opposite -direction to piston 2. Piston 3 is thus the fourth to move under power, -and it is followed by another power stroke by piston 1; the _firing -order_ is then said to be 1, 2, 4, 3. - -If it is piston 3 that follows piston 1, piston 4 will again be the -third to produce power, and piston 2 will be the fourth. The firing -order will then be 1, 3, 4, 2. There is no other order in which a -4-cylinder engine can produce power, and there is no choice between -them. - -The firing order of an engine is established by the manufacturer, and -depends on the order in which the valves are operated. - - - - -CHAPTER III - -ENGINE PARTS - - -The foundation of an engine is the _base_, which supports the -_bearings_ in which the crank shaft revolves, and to which the -cylinders are attached. The cylinders of tractor engines are made -of cast-iron, and the cylinder heads, which close the upper ends of -the cylinders, are usually in a separate piece, bolted on. The joint -between the cylinders and the cylinder head is made tight by placing -between them a _gasket_ of asbestos and thin sheet metal. - -The crank shaft has as many cranks, or _throws_, as the engine has -cylinders. Crank shafts for 2-cylinder engines are shown in Figure 7; -the upper one is for an engine of the type shown in Figure 3, with -pistons moving in the same direction. With both cranks projecting from -one side the shaft is out of balance, so _balance weights_ are attached -to the opposite side. - -[Illustration: FIG. 7.—2-CYLINDER CRANK SHAFT] - -The other shaft shown in Figure 7 does not need balance weights, for -one crank balances the other. A four-cylinder crank shaft, Figure 8, is -also in balance. - -[Illustration: FIG. 8.—4-CYLINDER CRANK SHAFT] - -[Illustration: FIG. 9.—HALF OF A PLAIN BEARING] - -Crank shafts revolve in _main bearings_, which are set in the engine -base. In tractor engines these are usually _plain bearings_, a half of -such a bearing being shown in Figure 9. This is a bronze shell lined -with a softer metal, making an exact fit on the shaft; with the two -halves in place, the shaft should turn freely, but without looseness or -side play. The grooves shown are to admit lubricating oil. - -[Illustration: FIG. 10.—CONNECTING ROD BEARINGS] - -[Illustration: FIG. 11.—PISTON COMPLETE AND IN SECTION] - -The _piston_ is attached to the crank shaft by a _connecting rod_, -which is illustrated in Figure 10. Pistons are shown in Figures 11 and -12; they are made as light as is consistent with the pressure that they -must bear, and are hollow, and open at the lower end. - -The piston is attached to the connecting rod by a _wrist pin_, or -_piston pin_, which is a shaft passing through it from side to side, -and also through the bearing in the upper end of the connecting rod. -The connecting rod swings on the wrist pin in following the rotation of -the crank shaft, and its attachment to the wrist pin must permit this -without being loose. - -The bearings at the two ends of a connecting rod are usually -adjustable, so that wear can be taken up; some of the methods of -doing this are illustrated in Figure 10. In A, the wrist pin bearing -is a plain tube, ground to an exact fit; when it is worn it must be -replaced. In B, the bearing is split, and the ends are drawn together -by a bolt to the correct fit. The bearing in C is in two parts, held -together by a U-shaped bolt, while in D the two parts are held together -by a cap bolted to the end of the connecting rod. In E, the end of the -connecting rod is a square loop enclosing the two parts of the bearing; -the parts are held in the proper position by a wedge adjusted by screws. - -The crank shaft bearing of the connecting rod shown in F is in two -parts which are hinged together. G, H, and K show the forms usually -used in tractor engines, which consist of two parts bolted together. - -[Illustration: FIG. 12.—WRIST PIN FASTENINGS] - -The wrist pin is usually firmly attached to the piston, so that the -connecting rod swings on it; methods of securing the wrist pin are -shown in Figure 12, the wrist pin being held in supports cast in the -piston. In A, the wrist pin is held by two set screws, and in B, by -pins passing through it. The wrist pin shown in D is hollow, as is very -common, and a bolt passes through part of the piston and into the wrist -pin. - -In the construction shown in C the wrist pin is secured to the -connecting rod and moves in bearings in the piston. In E, a ring -fitting in a groove around the piston prevents the wrist pin from -moving endways. - -The engine must usually be taken to pieces in order to get at the wrist -pin; lock nuts, lock washers or cotter pins are always used to prevent -the trouble that would be caused if the wrist pin worked loose. - -A leak-proof joint between the piston and the cylinder is made by means -of _piston rings_ that fit in grooves around the piston, as shown in -E, Figure 12. Piston ring grooves are shown in Figure 11. Piston rings -are not solid, but are split so that they are elastic; they fit snugly -in their grooves, and tend to spring open to a greater size than -the cylinder. This causes them to maintain a close fit against the -cylinder, and the gases are prevented from leaking past. - -[Illustration: FIG. 13.—VALVE] - -Each cylinder is provided with two valves: the _inlet valve_ that -admits fresh mixture and the _exhaust valve_ through which the burned -gases escape. These valves are metal disks with funnel-shaped edges -fitting into funnel holes. A valve and its stem are shown in Figure 13 -and also in Figure 15. - -[Illustration: FIG. 14.—ACTION OF A CAM] - -A valve is opened at the proper time by a _cam_, and closed by a -spring. A cam is a wheel with a bulge on one side, so that its rim is -eccentric to its shaft, as illustrated in Figure 14, which shows a cam -in three positions of a revolution. A rod resting on the rim of the -cam is moved endways as the bulge passes under it, and the valve is -operated by connecting it with the rod. - -A valve is opened once during two revolutions of the crank shaft; -therefore the cam cannot be placed on the crank shaft, for, if it -were, the valve would be opened every revolution. The cam is placed on -a separate shaft which is driven by the crank shaft at half its speed. -This is usually done with gears, a gear on the crank shaft meshing with -a gear on the cam shaft having twice as many teeth; the crank shaft -gear must make two revolutions in turning the cam shaft gear once. - -The valve in Figure 13 is held on its seat by a spring. The cam bears -against the end of the valve stem, and as it revolves its bulge forces -the valve stem and valve to move endways and thus to uncover the valve -opening. - -As the movement of the piston depends on the crank shaft, the valve can -be made to open at the right time by a proper setting of the gears that -drive the cam shaft. - -The length of time that the cam will hold the valve open depends on -the shape of the bulge of the cam. It can be seen that the pointed cam -of Figure 13 will not hold the valve open for as long a time as the -flat-end cam of Figure 14. - -[Illustration: FIG. 15.—“TWIN CITY” TRACTOR ENGINE] - -In the design shown in Figure 13 the cam bears directly against the -end of the valve stem, the cam shaft in this case lying along the -cylinder head. In the construction shown in Figure 15 the valves are -not placed in the cylinder head, but are in an extension or _valve -pocket_ projecting from the combustion chamber; this cam shaft is near -the crank shaft. It would not be practicable to make the valve stem -long enough to reach down to the cam, so a length of rod, called a -_push rod_, or _tappet_, is placed between them; the cam moves the push -rod and the push rod in turn moves the valve. This is a construction -frequently used for automobile engines. - -[Illustration: FIG. 16.—“HART-PARR” VALVE MECHANISM] - -In tractor engines the cam shaft is usually placed near the crank -shaft, as in Figure 15, and the valves are in the head, so that a valve -moves in the opposite direction to the movement of the push rod. This -requires still another part to be used, called the _rocker arm_. It is -shown in Figure 16. It is a short bar, pivoted at or near the center, -with one end at the push rod and the other at the valve stem. When it -is moved by the push rod it in turn moves the valve. - -Valves operated by push rods and rocker arms are also shown in Figures -17, 18 and 19; Figure 18 is a single-cylinder horizontal engine, while -Figure 19 is a horizontal double opposed engine, in which one cam -operates a valve in each cylinder. Figure 20 shows the valve mechanism -of a vertical engine in which all parts, including the rocker arm, are -enclosed to protect them from dust, and so they can run in oil. - -A small space is always left somewhere between the cam and the valve -stem, to give the valve stem room to lengthen, which it will do when it -gets hot. If this space were not left, the valve stem, in lengthening -as it became hot, would strike the part next to it, and the valve would -be lifted from its seat. This would cause the engine to lose power. -This space must be kept properly adjusted, and instructions for this -will be found in Chapter XII. - -[Illustration: FIG. 17.—“HART-PARR” ENGINE] - -A valve is held against its seat by a spring, which must be compressed -when the valve is opened. If this spring is too weak, it will not hold -the valve tightly on its seat, while if it is too stiff, the cam shaft -and other parts will be needlessly strained in compressing it. - -Friction between the cam and the end of the valve stem or push rod -would cause rapid wear if these parts were not of hardened steel, and -kept well oiled. Still further to reduce wear, there is usually a -roller on the end of the push rod, as shown in Figure 16 and some of -the other illustrations. Figure 15 shows a construction in which the -end of the push rod is a flat disk, which rotates as the cam comes into -contact with it. - -[Illustration: FIG. 18.—“OIL-PULL” ENGINE] - -When the mixture burns, the top of the piston, the cylinder head, and -the walls of the combustion chamber become heated, and if it is not -prevented they will get so hot that they will expand sufficiently to -cause the piston to stick, or _seize_. The upper part of the cylinder -is, therefore, provided with a cooling system that keeps these parts -from getting overheated. Channels are provided through which water is -circulated; the water takes the heat from the metal parts, becoming -heated itself, and then passes to a _cooler_, or _radiator_, where it -gives up the heat to currents of air. - -In addition to the channels, or _water jackets_, around the cylinder, -a cooling system includes the radiator, the connections, and usually a -pump that keeps the water in motion. - -[Illustration: FIG. 19.—HORIZONTAL DOUBLE OPPOSED ENGINE] - -In some tractors, notably the Fordson, no pump is used; the water -circulates because it is heated. This is called a _thermo-syphon_ -system. When the engine runs, the water in the cylinder jackets becomes -heated; as hot water is lighter than cold water, it rises and flows out -of the jackets to the radiator, its place being taken by cool water -from the bottom of the radiator. This circulation continues as long as -the water in one part of the system is hotter than the water in some -other part of the system. - -The lubrication of an engine is described and explained in Chapter X. - -[Illustration: FIG. 20.—“MONARCH” ENGINE] - - - - -CHAPTER IV - -FUELS AND CARBURETION - - -In order that a thing may burn, it must be provided with oxygen. Oxygen -is found in air, so it is usual to say that air is necessary in order -that anything may burn. - -To prove this, light a candle and place an empty bottle over it, upside -down; in a very short time the oxygen in the bottle will be used up, -and the flame will flicker and get smoky, and finally die out. If a -card is laid on the chimney of a coal-oil lamp so that it covers the -opening, that flame also will flicker, get smoky and go out. - -In order to deaden the fire in a stove, the dampers are closed to -prevent air from entering; the fire is kept alight by the very small -quantity of air that leaks in below the fire-box. When the drafts are -opened the fire will burn up brightly because a plentiful volume of air -can then enter. - -In a similar way, air must be used in a gas engine in order that the -fuel may burn. It is not possible to mix air with a liquid; the first -step in making a gas that will burn is, therefore, to turn the fuel, -whether it is gasoline, kerosene, distillate, or other oil, into a -vapor; this vapor is then mixed with air. - -For good results it is very necessary that the vapor and air be in -proper proportions. In the experiment with the candle and the bottle it -was seen that as the air was used up, the candle flame became yellow -and smoky: this is the effect of insufficient air. If there is not -enough air in the mixture, part of the vapor will not be able to burn, -and will only smoke. - -If, on the other hand, there is too much air, the mixture, if it will -burn at all, will burn slowly, and the extra volume of air will reduce -the heat. - -In a mixture of the proper proportions of air and fuel vapor, the -burning, or _combustion_, will be very rapid, resulting in the sudden -production of the greatest possible amount of heat. This, of course, is -what is necessary if the engine is to produce its fullest power. With -such a mixture, combustion will be complete before the piston has done -more than start outward on the power stroke, and the greatest possible, -or _maximum_, pressure will then be produced. - -When a mixture burns slowly, the piston will have gone through much -of the power stroke before combustion is complete, in which case a -considerable part of the pressure that should have been applied at the -beginning of the stroke will be wasted. - -A mixture that is not correct will burn unevenly; it may burn better -during one power stroke than during another, which will make the engine -run unsteadily. - -If the mixture has too much air in proportion to the amount of vapor, -it is known as a _thin_ mixture, or a _lean_ or _poor_ mixture. It -burns so slowly that it is quite possible for the mixture that started -burning before the beginning of the power stroke to continue burning -through the exhaust stroke, and for enough flame to remain in the -cylinder to set fire to the fresh charge that enters during the next -inlet stroke. This will produce what is known as a _backfire_; that is, -the mixture entering the cylinder will catch fire, and in burning will -blow back through the open inlet valve. This is a dangerous condition, -for the flame might spread to fuel dripping from the carburetor, or to -the fuel tank. - -A mixture that has not enough air is called a _rich_ mixture; the air -that is present will burn part of the vapor, while the rest will go out -of the exhaust unburned, or will work past the piston into the oil in -the crank case. This is wasteful of fuel. - -The most serious result of a rich mixture, however, is in the -production of _carbon_, and the _carbonization_ of the engine. The -flame of a rich mixture is smoky; the smoke of this flame, as is the -case with smoke from all other sources, is composed of fine particles -of carbon, or soot. These particles of carbon will deposit on all parts -of the combustion space: on the top of the piston, on the valves, on -the spark plugs, and on the inner wall of the cylinder head. At first -it is gummy, but it rapidly hardens and forms a crust that must be -scraped off with a steel tool. - -Carbon in an engine will reduce the power through causing -_preignition_, or, in other words, by setting fire to the fresh charge -before the proper point in the stroke. The heat of the combustion will -cause the carbon deposit to become so heated that it will glow, these -glowing particles being sufficient to ignite the incoming fresh charge. -The remedy for this condition is to remove the carbon, which is usually -done by taking off the cylinder head and scraping away the deposit. - -It may be added that carbon is also formed by the use of too much -lubricating oil, as will be explained in the chapter on lubrication. - -Thus it is seen that if the engine is to run properly, and is to be -kept in good condition, the proportions of the mixture must be very -carefully maintained. - -The mixture is formed in a _carburetor_, or _mixer_. This is, roughly, -in the form of a tube through which air is sucked during the inlet -stroke; projecting into it is a fine tube called a _spray nozzle_ -through which the fuel enters. In action it is somewhat similar to the -atomizer that is used for spraying the nose and throat. By forcing the -fuel to flow rapidly through this small tube it comes out in the form -of spray, and the tiny drops are picked up by the current of air and -are carried into the cylinder. - -It is much easier to form a mixture of gasoline than of kerosene or -distillate, because gasoline vaporizes more readily at ordinary -temperatures. If saucers of gasoline and kerosene are placed in the -sun, the gasoline will evaporate rapidly and completely, leaving only -a faint oily deposit. The kerosene, on the other hand, will evaporate -slowly, and much of it will not evaporate at all. - -To make kerosene and distillate evaporate completely, they must be -heated, just as water must be heated to make it evaporate. - -In the case of a carburetor for gasoline, the current of air needs -only to be warmed; the spray of gasoline will evaporate on coming into -contact with the warmed air, and much of it will enter the cylinder as -vapor. In order to evaporate kerosene and distillate much more heat -must be provided, and it is usually considered necessary to heat not -only the current of air, but the liquid fuel as well. Methods of doing -this will be explained in the next chapter. - -[Illustration] - -[Illustration: FIG. 21.—PRINCIPLE OF CARBURETOR] - -When kerosene or distillate is used, there are conditions that make -it necessary to add water vapor to the mixture, which prevents the -overheating of the cylinder and reduces the deposit of carbon. The -difficulty of making a complete vapor of kerosene and distillate -results in a tendency on the part of these fuels to carbonize the -cylinders; the use of water aids in keeping the cylinders clean. - -The general principle of a carburetor is shown in Figure 21, one -drawing illustrating conditions when the inlet valve is closed and the -other when it is open. It shows an engine cylinder connected with an -inlet pipe or _mixing chamber_, through which there is a swift flow of -air during an inlet stroke. - -Projecting into the intake pipe is the _spray nozzle_, which is -connected with a small chamber containing fuel; inside of this chamber -is a _float_, usually made of cork, although it is sometimes a light -metal box. The fuel is intended to fill the chamber to a certain -height, at which the valve will be closed by the float rising on the -fuel. This level is such that the fuel does not quite reach the tip of -the spray nozzle. - -During the compression, power, and exhaust strokes, the fuel stands at -this level, for it cannot run out of the spray nozzle, and the float -holds the valve closed. As soon as the inlet valve opens, air rushes -through the intake pipe and sucks fuel out of the spray nozzle. This, -of course, takes fuel out of the float chamber; the float in sinking -opens the valve, and enough fuel enters to restore the level. - -The fuel comes out of the nozzle in the form of fine spray; it is in -such small drops that it evaporates quickly, and the resulting mixture -of fuel vapor and air passes into the cylinder. By using a spray nozzle -of the proper size, any desired proportion of fuel and air may be -obtained. - -If an engine runs at a single speed, a carburetor as simple as this one -would be satisfactory, for if the suction is always the same, there -will be little or no change in the proportions of the mixture that is -formed. - -To get the best results, the proportions of fuel vapor and air should -be the same for all running speeds of the engine. The proportions of -the mixture, however, depend on the violence of the suction, which -changes as the engine speed changes, becoming greater as the speed -increases. The simple carburetor illustrated in Figure 21 can be -adjusted to give a correct mixture for any particular speed, but will -be out of adjustment for any other speed. - -The speed of a 1-cylinder engine does not change very greatly; it is -built to run at practically a constant speed, and a simple carburetor -is satisfactory for it. The speed of engines with a greater number of -cylinders may be greatly changed, and the carburetor must be so made -that it will give the same proportions of vapor and air at low speed as -at high. - -In the simple carburetor described, the speeding-up of the engine will -result in a greater rush of air through the intake pipe, which in turn -will suck out a much greater quantity of fuel. If the carburetor is -adjusted to give the proper quantity of fuel for the air that passes -at low speed, at high speed it will give far more fuel than will be -required by the quantity of air that then passes. Thus at high speed -the mixture will be too rich. - -If, on the other hand, this carburetor is adjusted to give a proper -mixture at high speed, too little fuel will be sucked out when the -engine runs slowly, and the mixture will be too lean. - -A carburetor must thus have an additional device that will keep the -mixture correct, regardless of the speed at which the engine runs. -This is sometimes done by changing the size of the spray nozzle so -that a greater or less quantity of fuel flows out, but more usually -by permitting an extra quantity of air to enter the carburetor as -the engine speeds up. This is done with an _extra air intake_, the -principle of which is illustrated in Figure 22. - -As will be seen, this carburetor has two openings for air, one being -the main air inlet and the other the extra air inlet. The latter is an -opening provided with a valve which is held on its seat by a spring. -The suction created by an inlet stroke is exerted in the carburetor, -but at low speed is not sufficient to suck the extra air valve from its -seat. Air then enters only through the main air inlet, and the spray -nozzle is adjusted to give the proper proportion of fuel. - -[Illustration: FIG. 22.—PRINCIPLE OF EXTRA AIR INLET] - -As the engine speed increases the mixture becomes richer; but there -is also an increase in suction, which becomes strong enough to pull -the extra air valve from its seat. This provides another opening into -the carburetor, through which enough air enters to keep the mixture -in proper proportion. The higher the speed of the engine the more the -valve will open, and the greater will be the quantity of air admitted. - -In order to get the fullest power from an engine, the carburetor is -built to give its most perfect mixture at the usual working speed. -This will be the speed at which the engine will run under ordinary -conditions. As the engine will run at this speed most of the time, the -carburetor should then deliver its best mixture on the least possible -quantity of fuel. - -As an engine is run at low speed so little of the time, it is not -necessary that the mixture should then be so perfect or that the fuel -should be used so economically. - -The design of a carburetor is a complicated matter, because the -production of mixture is due to the flow of air, which is a very -changeable thing. On a cold, damp day, the air will be heavier and -denser than on a day that is hot and dry, and different quantities of -fuel will be necessary for the formation of the mixture. The carburetor -manufacturer cannot make a commercial carburetor that will take care -of such a difference as this; he strikes an average that gives good -general results, and expects the user to change the adjustments when -weather and temperature make it necessary. - -The formation of the mixture is affected by the condition of the -engine. When all of the parts of the engine are tight, the suction in -the carburetor is more violent than when there is a leakage of air past -the piston rings, or through a leaky valve or spark plug. - -On a dry, hot day the fuel evaporates much more readily than on a -day that is cold and damp; more of the fuel that flows out of the -spray nozzle will be vaporized and the formation of the mixture will -be easier. On a cold, damp day the fuel will not vaporize in the -carburetor to any extent, and much of it will pass to the cylinder in -drops that even there will not vaporize in time to form a mixture. -In order to assure the vaporization of enough fuel to form a mixture -under such conditions, the fuel and the air must be heated to a greater -degree. - -As the engine becomes heated up, more and more of the fuel will -vaporize, and the amount flowing out of the spray nozzle may therefore -be cut down. - -With fuels like kerosene and distillate, which do not vaporize as -readily as gasoline, it is not unusual to have them condense on the -walls of the inlet pipe, which produces a condition known as _loading_. -This condensation is similar to the sweating of an ice-water pitcher -on a hot day. If an engine is running at a constant speed, loading -does not make much difference, because the carburetor is so adjusted -that it gives a proper mixture. If the engine is suddenly speeded up, -however, the greater rush of air will pick up the condensed fuel, and -the mixture will instantly become too rich, continuing so until this -extra supply of fuel is used up. The result will be to choke the engine -and make it lose power just at the time when extra power is needed. - -Loading can be prevented by heating the inlet pipe to such an extent -that the fuel will not condense on it. - -The speed of a tractor engine is practically always controlled by a -_throttle_, which is a valve set in the passage of the carburetor. -It operates exactly the same as a damper in a stovepipe; when it is -closed, it shuts the passage and prevents the flow of mixture to the -engine. As it is opened, it permits a greater quantity of mixture to -flow, and it follows, of course, that as the charges of mixture become -larger, the engine runs with more power. A tractor carburetor usually -has two throttles, one being operated by hand and the other by the -governor. - -It is usual for a carburetor to be fitted with a _strangler_, or -_choke_, which makes it easier to form a mixture at slow starting -speed. When an engine is cold, the fuel evaporates slowly; and, -furthermore, when an engine is cranked by hand its speed is so low that -the suction in the carburetor is not sufficient to draw out enough fuel -to form a mixture. The strangler is a valve similar in every way to the -throttle, but placed between the main air inlet and the spray nozzle. -When it is closed and the engine is cranked, very little air can enter -the carburetor; the suction is therefore very great. Far more fuel -than usual is then sucked out of the spray nozzle, and of this greater -amount enough reaches the cylinder to form a combustible mixture. The -engine will start, but as soon as it does so, the strangler must be -opened so that the normal amount of air enters. If this is not done, -the excessive suction will draw so much fuel out of the spray nozzle -that the mixture formed will be too rich to burn. - - - - -CHAPTER V - -CARBURETORS - - -The apparatus that forms the mixture is in two parts, one being the -carburetor that proportions the fuel to the quantity of air drawn into -the cylinder, and the other the _mixing chamber_, or _manifold_, that -connects the carburetor with the valve chamber. The mixing chamber has -no adjustments; it is a passage, often a pipe, that is shaped to fit -the conditions, and according to the ideas of the manufacturer. When -kerosene and distillate are used, the mixing chamber must be heated, so -it is frequently built into the _exhaust manifold_, which is the pipe -that conducts the burned gases away from the engine. In some cases it -gets heat from the water jacket of the engine, a water jacket formed -around it being connected with the cooling system. - -The carburetor, on the other hand, has adjustments that must be -understood in order to run the engine economically. The understanding -of these adjustments is simplified if it is remembered that the object -of the carburetor is to maintain a correct proportion of fuel to the -volume of air that passes through it. - -All tractor carburetors operate on the same principles, and the -principles are applied in much the same way. If these principles are -understood, and there is an understanding of what the parts of a -carburetor are for and what they do, there should be no difficulty in -adjusting and caring for any kind of a carburetor that may be offered. - -The main body of the carburetor is the tube through which the air -passes. This is a casting, and cannot be adjusted or altered. Into this -passage projects the spray nozzle, which is usually provided with an -adjustment to control the amount of liquid that may flow out of it. -When no adjustment is provided, the spray nozzle is made removable, so -that a nozzle with an opening of any desired size may be inserted. - -[Illustration: FIG. 23.—“KINGSTON” CARBURETOR, MODEL L] - -On some carburetors the extra air valve is set by the manufacturers, -while on others it is adjustable by controlling the strength of the -spring that holds it against its seat. - -The carburetor shown in Figure 23 has a spray nozzle adjustment of a -very usual type. A rod is so arranged that its pointed end projects -into the opening of the spray nozzle; by screwing it up or down the -opening may be made larger or smaller, so that more or less fuel may -flow out. The extra air valve is a flap valve that closes the air -passage until the suction is great enough to lift it from its seat. -Around the spray nozzle is a tube that connects the passage below the -extra air valve with the passage above it; when the suction is too low -to lift the extra air valve from its seat, any air flowing through the -carburetor passes through this tube. The tube is so small that even a -little air passing through it is enough to suck fuel out of the spray -nozzle, and the spray nozzle is so adjusted that enough fuel comes out -to make a proper mixture with that volume of air. - -This is the _low-speed adjustment_, which gives a mixture on which the -engine will start and will run at its lowest or _idling_ speed. At this -speed the engine produces just enough power to keep itself going. - -When the engine speeds up, and suction increases, the extra air valve -is lifted off its seat, and a greater volume of air flows through the -carburetor. The increased suction also draws more fuel out of the spray -nozzle. If the greater amount of fuel were in proportion to the greater -volume of air, there would be no change in the mixture, but this is not -the case. As suction increases, the proportion of fuel drawn out of the -spray nozzle becomes too great for the air, and the mixture becomes too -rich. To overcome this, the extra air valve permits a still greater -volume of air to pass, so that the proportions of fuel and air do not -change. - -The chamber below the air passage in Figure 22 is the fuel cup, into -which fuel flows from the tank. Inside the fuel cup is a ring of cork -attached to a pivoted lever, on the other end of which is a needle -valve that can close the opening through which the fuel enters the cup. -As the cup fills, the cork floats on it, and in rising it moves the -lever on its pivot. When the fuel reaches such a level that it is near -the tip of the spray nozzle, the valve closes the opening and prevents -more fuel from entering. - -[Illustration: FIG. 24.—“KINGSTON” CARBURETOR, MODEL E] - -In the carburetor shown in Figure 24, the principal air passage is past -the spray nozzle, and all air goes by this passage when the engine -is running at low speed. The extra air inlet consists of a number of -holes through which air can pass without going past the spray nozzle. -On each of these holes is a ball; when the suction is low the balls -completely close the holes. When speed increases, the suction becomes -great enough to lift the balls off the holes, and the extra volume of -air that is necessary is permitted to enter. By making the balls of -different weights, it can be seen that the volume of air admitted for -any speed is under good control. - -Like the carburetor shown in Figure 23, this carburetor is of the -_float feed_ type; that is, the flow of fuel to it is controlled by a -valve that is operated by a float. - -Either of these two carburetors may be adjusted for gasoline or for -kerosene, but the adjustment that is right for one is wrong for the -other. Thus, if an engine is started on gasoline, with the intention of -running on kerosene, the carburetor must be readjusted when the change -is made. This is unsatisfactory, so a double carburetor is sometimes -used, as shown in Figure 25. This consists of two carburetors of the -kind shown in Figure 24, having a single mixture outlet, one being -adjusted for gasoline and the other for kerosene. Either of them can be -connected with the mixture outlet by means of a switch valve. - -[Illustration: FIG. 25.—“KINGSTON” CARBURETOR, DUAL MODEL] - -In order to run on kerosene or distillate it is necessary to apply heat -for the reason that these oils do not evaporate readily at ordinary -temperatures. Gasoline, on the other hand, evaporates readily, and a -cold engine can be started on it. Tractors that run on kerosene or -distillate are therefore started on gasoline and run on it until they -are hot enough to vaporize the heavier oil. - -A carburetor that will run on either gasoline or kerosene is shown in -Figure 26. The main air inlet is at E, which leads the air around the -spray nozzle and into the chamber G. The mixture flows to the cylinder -by the passage B. The control of the fuel at working speeds is by the -high-speed adjustment, which is a needle valve screwing into the spray -nozzle. Above this is another needle valve that adjusts the flow of -fuel for slow speed. - -Extra air enters through the opening A, which is closed at slow speed -by a valve held against it by a spring. This valve bears against one -end of a pivoted lever, the other end of which is attached to the -slow-speed needle valve; when the extra air valve opens it moves the -lever and the slow-speed needle valve is lifted to permit the flow of a -greater volume of fuel from the spray nozzle. - -[Illustration: FIG. 26.—“E-B” CARBURETOR] - -This carburetor is started on gasoline. When the engine is hot, a -switch valve is operated to permit the burned gases from the engine to -flow through the carburetor; they pass through the pipe C, D, and as -the chamber G is directly in their path it becomes intensely heated. -The carburetor can then be switched to kerosene. A side view of this -carburetor is shown in Figure 27. - -These carburetors are all of the float feed type, and are used on -engines of which the speed is variable. A carburetor that is fed by a -pump is shown in Figure 28. This is a simple tube with a fuel cup cast -on one side of it. Fuel is pumped to the bowl, and the proper level is -maintained by an overflow through which excess fuel passes back to the -tank. - -This carburetor is intended for an engine of which the speed does not -change greatly. Its only adjustment is the spray nozzle, and this is -altered to correspond with changes in engine speed. - -[Illustration: FIG. 27.—“E-B” CARBURETOR, SIDE VIEW] - -[Illustration: FIG. 28.—PUMP-FED CARBURETOR] - -If an engine is clean and in good condition, it will run as well on -kerosene as on gasoline, although the heating effect of kerosene is -greater. When an engine is carbonized, as is usually the case, a -condition known as _preignition_ will occur unless it is prevented. -Carbon from unburned fuel or from lubricating oil will deposit on the -piston head and the parts of the combustion chamber, and particles will -become heated to the glowing point, when they will set fire to the -fresh mixture during the compression stroke and before the proper time. -The effect is to make the engine lose power, and it also gives rise to -a sharp metallic knocking. By reducing the temperature in the cylinder -during the compression stroke this condition can be prevented. This can -be done by adding water vapor to the mixture, and kerosene carburetors -are therefore built with a water attachment. As can be seen in Figure -28, this is a water cup and spray nozzle like those for the fuel. When -the engine knocks, and shows that preignition is occurring, water is -turned on, and, being carried into the cylinder, keeps the mixture from -being heated to the point of ignition before the proper time. - -Figure 29 shows the attachment of this carburetor to an engine which, -in this case, is horizontal. To start the engine, gasoline is injected -into the carburetor, as shown; this will give a sufficiently good -mixture for the purpose, and enough heat for running on kerosene is -thus obtained. - -[Illustration: FIG. 29.—“TITAN” CARBURETOR] - -[Illustration: FIG. 30.—PUMP-FED CARBURETOR WITH TWO FUEL NOZZLES] - -The carburetor shown in Figure 30 is similar, but has a bowl and spray -nozzle for gasoline, to use in starting. It is also provided with a -heating jacket through which hot water or hot gases may circulate. - -In many cases the fuel is heated before reaching the carburetor. This -is done by coiling the feed pipe around the exhaust pipe or putting it -in a jacket through which hot water circulates. - -Another device sends the mixture through a chamber heated by the -exhaust, as shown in Figure 31. Figure 32 shows an arrangement in which -the mixture passes through a jacket around one branch of the exhaust -pipe. By means of a switch valve, A, more or less of the exhaust gases -may be permitted to flow through this branch, so that the mixture may -be heated to any desired degree. - -[Illustration] - -[Illustration: FIG. 31.—“HART-PARR” MIXTURE HEATER] - -All of these heating devices are so arranged that the heat is under the -control of the driver, which permits him to heat the mixture as much as -he judges to be necessary. Enough heat must be used to prevent the fuel -from condensing; but too much heat will cut down the efficiency of the -engine because it will cause so much expansion of the mixture that a -cylinderful of it will not produce the maximum power. - -[Illustration: FIG. 32.—“TWIN CITY” MANIFOLD] - -Figure 33 shows the pump that is used in a force feed carburetor of the -type shown in Figure 28. Its plunger is forced through an inward stroke -by a cam, and makes an outward stroke as its spring returns it to -position. The inlet and outlet openings of the cylinder are closed by -ball check valves, the inlet check being open on the outward strokes, -and the outlet check being open on the inward strokes. A pump of this -sort requires no attention beyond seeing that the check valves work -properly, and that there are no leaks. - -Figure 34 shows the connections between the fuel tank and the -carburetor. Under the tank, 1, is a chamber containing a fine wire -strainer, 4, through which the fuel must pass to reach the carburetor; -any dirt that may be present is strained out, and collects in the cup, -2. Water in the fuel also settles here, and the cup is cleaned out by -unscrewing the plug, 3. 5 is the shut-off cock; it should always be -closed when the tractor is not working. - -[Illustration: FIG. 33.—FUEL PUMP] - -A complete fuel system is illustrated in Figure 35, showing the -connections of the tanks, pumps, and carburetor. - -As dirt is injurious to an engine, the air that forms the mixture -must be clean, so when a tractor works in a dusty field, it should be -equipped with an air cleaner, of which there are three kinds. In one -of these the air is required to pass through water, which washes it. -A cleaner of this type is shown in Figure 36. The dusty air enters -the central passage, and is forced to pass through the water in order -to reach the outlet. Passage through the water and through the baffle -plates frees the air of all its dust. - -In the cleaner shown in Figure 37, the air is passed through loose -wool, which filters out the dust. Another type of cleaner works on -the same principle as a cream separator; the air is given a whirling -motion, which throws the dirt out at the sides, and it is collected in -a glass jar. - -[Illustration: FIG. 34.—“AVERY” FUEL CONNECTIONS] - -[Illustration: FIG. 35.—“OIL-PULL” FUEL SYSTEM] - -These air cleaners must be emptied frequently, for if they are not kept -clean it cannot be expected that they will do their work. - -A tractor engine is built to develop its maximum power at a certain -speed; if it runs at greater speed, it will not operate efficiently, -and there will be unnecessary wear of its parts. These engines are -therefore usually fitted with _governors_ which hold them at their most -efficient speed. A governor operates by _centrifugal force_. - -Anything in motion tries to move in a straight line; if it is forced to -move in a circle, it will exert force in trying to move away from its -center. It is this that is called centrifugal force. It is centrifugal -force that holds water in a pail that is being swung around the head, -and that makes the pail fly off if it is released. - -[Illustration: FIG. 36.—AIR WASHER] - -In applying this principle to a governor, weights are attached to a -plate and made to revolve; springs hold them together, but in spite -of this, centrifugal force throws them outward. In moving, they act -on a rod that operates the throttle; as the speed increases, the move -outward more and more, and it is a simple matter of adjustment to cause -them to close the throttle when the speed reaches a desired point. - -[Illustration: FIG. 37.—AIR STRAINER] - -[Illustration: FIG. 38.—“E-B” GOVERNOR] - -A governor and its connections are shown in Figure 38. The weights, -R, are L-shaped, and pivoted at the angle to a plate driven by the -engine. The shaft that drives the plate also supports a collar, P, that -is loose on it and can slide endways; the collar rests against the -short bar of the L-shaped weights. The other end of the collar touches -the lever, E, which is moved when the collar moves. As the lever is -connected with the throttle, a movement of the collar will control the -position of the throttle. - -[Illustration: FIG. 39.—“CASE” GOVERNOR] - -When the shaft revolves, the long arms of the L-shaped weights tend -to fly outward; this moves them on their pivots, and the short arms -thereupon force the collar to slide on the shaft, which moves the lever -and operates the throttle. The speed at which the throttle will begin -to close is determined by the setting of the spring that holds the -weights in. - -[Illustration: FIG. 40.—“HART-PARR” GOVERNOR] - -Governors and governor connections are shown in Figures 39 and 40. - -The governor shown in Figure 41 is enclosed in a housing that can -be locked or sealed. This prevents the unauthorized changing of the -adjustment. - -[Illustration: FIG. 41.—VERTICAL GOVERNOR] - - - - -CHAPTER VI - -IGNITION - - -In order that a gas engine may run properly, the mixture must be set on -fire, or _ignited_, at exactly the right time; if ignition occurs too -early or too late, there will be a loss of power. - -The greatest pressure will be obtained at the instant when all of the -mixture is burning, and this should take place just as the piston -begins to move outward on the power stroke. A little time is required -for the mixture to burn; there is a brief interval between the instant -when it is set on fire and the instant when it is all in flame. Thus it -is clear that if the mixture is all to be burning as the piston starts -the power stroke, it must be set on fire before that time, or, in -other words, toward the end of the compression stroke. - -The point at which ignition should occur depends on the speed of the -engine and should change when the speed changes. The time required -for the flame to spread throughout the mixture does not change; let -us say that, with the engine running at 1200 revolutions a minute, -the mixture can be ignited when the piston is ¼ inch from the end -of the compression stroke, and will all be in flame by the time the -piston starts on the power stroke. If the engine is slowed down to -600 revolutions a minute and no change is made in the ignition, the -mixture will all be in flame before the piston reaches the end of the -compression stroke; pressure will then be produced before the piston -is in position to perform the power stroke. The pressure will try to -make the engine run backwards; it will sometimes be sufficient to make -the engine stop. If the momentum of the flywheel is sufficient to -force the piston to the end of the stroke against the pressure, this -condition will cause a loss of power. This is called _preignition_, or -ignition that occurs too soon. One effect of it is to produce a hard, -metallic knocking, due to the oil being squeezed out of the bearings by -the great pressure, which permits the bearing and shaft to strike. The -remedy is to make ignition occur later in the stroke. - -If the engine is speeded up above 1200 revolutions, the piston will -have had time to move some distance on the power stroke before the -mixture is all in flame; the combustion space will then be too large to -permit the mixture to produce its greatest pressure, and again there -will be a loss of power. The remedy in this case is to make ignition -occur earlier in the compression stroke. - -When ignition is made to occur early in the compression stroke, it is -said to be _advanced_; when it is made to occur late in the stroke, it -is said to be _retarded_. - -To get the best results, the engine should be run with ignition -advanced as far as is possible without causing knocking. - -The charge of mixture is always set on fire by an electric spark, and -the parts that produce and control this spark are called the _ignition -system_. - -An ignition system consists of: First, the apparatus that produces the -electric current, which is usually a _magneto_; second, a _timer_, -which controls the instant at which the spark occurs; third, the _spark -plugs_, which project into the cylinders, and at which the sparks take -place; fourth, a _switch_, by which the sparking current can be turned -on or off, and fifth, the wires, or _cables_, by which the parts are -connected. - -The electric current that gives the spark is always produced by -magnetism. In a magneto, magnetism is obtained from the heavy steel -magnets that are part of it; there is a constant flow of magnetism from -one end of these to the other. To obtain an electric current, a coil -of wire is placed in the magnetism, and the strength of the magnetism -is made to change; it alternately becomes weak and strong. Whenever a -change in strength takes place, an electric current flows in the wire, -and it continues to flow as long as the magnetism continues to change -in strength. When the change in strength is very great, that is, when -the magnetism changes from very weak to very strong, or from very -strong to very weak, the electric current is more powerful than when -there is only a little change in strength. A more powerful current is -also produced by a change that takes place suddenly than by a change -that takes place slowly. - -The electrical principle that produces a current in this manner is -called _induction_; the current produced is known as an _induced_ -current. - -A magneto has two or more magnets, and between their ends, or _poles_, -there revolves a piece of iron called the _armature_. A piece of iron -placed between the poles of a magnet becomes a magnet itself; the -armature is so shaped that, as it revolves, its magnetism continually -changes in strength, and it is the changes in the strength of the -magnetism of the armature that produce the sparking current. - -[Illustration: FIG. 42.—ARMATURE] - -The iron armature of the Bosch magneto, which is the best known type, -is shown in Figure 42. It has a central bar with two heads, the wire -being wound around the central bar, or _core_. The shafts on which it -revolves are attached to the ends of the heads. - -Figure 43 shows different positions of the armature between the poles -of the magnet, and illustrates the changes in the magnetism of the -central bar. There is a continual flow of magnetism from one pole of a -magnet to the other; if a piece of iron lies between them the magnetism -will use it as a bridge, but often its easiest path will be through the -air. In A, Figure 43, the armature lies crossways, and its central bar -or core forms a perfect bridge for the magnetism. Practically all of -the magnetism flows through it, and it then becomes a powerful magnet -itself. It sets up its own flow of magnetism, which flows through the -core to one head, through the air to the other head, and so back to the -core. - -[Illustration: FIG. 43.—FLOW OF MAGNETISM THROUGH ARMATURE CORE] - -In B, the armature has revolved a little. Most of the magnetism is -still flowing through the core, but some of it is finding an easier -path by flowing through the heads and across the air space to the other -pole. The magnetism of the core is, therefore, a little weaker than it -is in A. - -In C, the heads alone form bridges between the poles, and none of the -magnetism flows by the core because that no longer forms a path. The -core is no longer producing magnetism; in moving from A to C there has -thus been a complete change in the strength of the magnetism of the -core, for from full strength it has died away to nothing. - -By a further movement, as in D, the core again acts as a bridge, and -another change in strength occurs, this time from nothing to full -strength again. In moving from D to B, there are slight changes in -strength, but not enough to produce a sparking current; it is only in -passing from B to D that a sparking current can be produced. - -In this type of magneto the space between the heads is wound full of -wire, which of course revolves with the armature; the more turns of -wire there are, the more intense will be the current, so very fine wire -is used to get the greatest possible number of turns. - -In the Bosch magneto the first few layers are of coarse wire, and are -the _primary winding_. The remainder, called the _secondary winding_, -is very fine wire, and the two are connected so that one forms an -extension of the other. - -It has been explained that it is most important to have the spark occur -at exactly the right instant in the stroke. On a magneto the instant of -sparking is controlled by a _timer_, or _circuit breaker_, which is a -switch that is automatically operated at the time when the magneto is -producing a current sufficiently intense to form a spark. - -Figure 44 illustrates one complete revolution of the armature, and -it will be seen that it passes twice from position B to position -D. This shows that it gives a sparking current twice during each -revolution. The circuit breaker must therefore operate twice during -each revolution. It is placed at the end of the magneto; in some makes -it revolves with the armature and is operated by stationary cams, while -in others it is stationary, and is operated by a cam on the armature -shaft. In either case the effect is the same. - -[Illustration: FIG. 44.—ONE COMPLETE REVOLUTION OF THE ARMATURE] - -[Illustration: FIG. 45.—CONNECTIONS OF BOSCH MAGNETO] - -Figure 45 shows the way in which the winding on the armature of a Bosch -magneto is connected with the circuit breaker and with the armature. -The circuit breaker shown is not the kind used on the Bosch, and serves -only to illustrate the principle. It consists of a lever pivoted at one -end, with the other end resting against the tip of a screw. A cam bears -against the lever and can move it to break the contact with the screw. -The cam is so set that it moves the lever at the time when the current -is most intense. - -The coarse wire, or primary winding, on the armature is connected with -the lever and with the screw of the circuit breaker; when the lever is -touching the screw, any current produced in the primary winding has a -complete path, or _circuit_, in which to flow. - -The fine wire, or secondary winding, is wound on top of the primary, -and its inmost end is connected to the outmost end of the primary -so that one forms a continuation of the other. The outmost end of -the secondary leads to the spark plug; any current produced in the -secondary winding flows to the spark plug, and, if intense enough, -will jump across the small gap in the plug, and return to the -secondary by way of the primary. - -Referring to Figure 43, a weak current is produced in the primary while -the armature revolves from D to B; at that time the circuit breaker is -closed, so the current can flow in the path thus provided for it. A -current also tries to flow in the secondary, but is too weak to jump -across the gap in the spark plug. As the armature comes closer to the -point C, Figure 43, the primary current becomes more intense, and the -electricity in the secondary increases its endeavor to jump the gap in -the spark plug, but is still unable to do so. - -As the armature passes over the point C, the circuit breaker opens. -The primary current, which is then most intense, finds its path taken -away from it, and it seeks another, which it finds by flowing into the -secondary winding. This flow of primary current, added to the pressure -already existing in the secondary, forms a current sufficiently -intense to jump across the gap in the spark plug, and in so jumping it -produces the ignition spark. - -As the armature passes to position D, Figure 43, the circuit breaker -closes, and the action is repeated. - -[Illustration: FIG. 46.—“K-W” INDUCTOR] - -A magneto of this type is thus seen to give two sparks to every -revolution of the armature. - -K-W and Dixie magnetos operate on the same general principle as the -Bosch, with the difference that the wire windings are separate from -the armature, and do not revolve. The revolving part, which is called -an _inductor_, consists of blocks of iron, so shaped that, as they -revolve, they alternately lead the magnetism to the core of the winding -and then away from it. The result is that the core gains magnetism and -then loses it, and these continual changes in strength produce sparking -currents in the winding. - -The inductor of a K-W magneto is shown in Figure 46. It consists of -a shaft on which are mounted two blocks of iron at right angles. The -section of shaft that joins them is the core of the winding; the wire -is wound on it just as thread is wound on a spool, but with a space -between, so that the shaft may revolve inside of the coil. - -Figure 47 shows the inductor in three positions of its revolution -between the poles of the magnet. When it is in the first position, -magnetism can flow from one pole of the magnet to the other by going -into one end, A, of one block, through the core, and out of one end, -C, of the other block. This makes a magnet of the core and it forms -magnetism of its own. When the inductor turns to the second position -magnetism can get across without flowing through the core, for the -blocks now give it a path. As the flow through the core ceases, the -core’s magnetism dies away, which gives the change in strength that is -needed to produce a sparking current. - -[Illustration: FIG. 47.—“K-W” INDUCTOR IN THREE POSITIONS] - -When the inductor is in the third position, the core again becomes the -path for the magnetism and is magnetized; these changes continue as -long as the inductor turns. - -[Illustration: FIG. 48.—“DIXIE” INDUCTOR] - -While an armature type of magneto, like the Bosch, produces two sparks -to every revolution, the K-W produces four, for there are four periods -during every revolution when there is sufficient change in the strength -of the magnetism of the core to produce a sparking current. - -In these magnetos the revolving shaft is parallel to the ends of the -magnets, but in the Dixie magneto it is at a right angle, as shown -in Figure 48. The shaft is of some metal, such as brass or bronze, -through which magnetism will not flow; otherwise the shaft would form a -continuous path. The inductor blocks are mounted on the shaft, and act -as extensions of the poles of the magnet. The core on which the wire is -wound is a separate piece, placed under the arch of the magnets, with -ends that extend down and form a tunnel in which the inductor revolves. - -Figure 49 shows an end view of the inductor, the magnets being cut -away so that the core may be seen. As inductor block A is an extension -of one pole of the magnet, magnetism tries to flow from it to block -B, which is an extension of the other pole of the magnet. When the -inductor is in position 1, Figure 49, magnetism can flow from block -A through the core to block B, the core then being magnetized. In -position 2, magnetism can flow from one block to the other by going -through the ends of the core instead of through the core itself; the -core then loses its magnetism, but regains it when the inductor moves -to position 3. - -[Illustration: FIG. 49.—THREE POSITIONS OF “DIXIE” INDUCTOR] - -In practically all makes of magnetos the circuit breaker is at the -end of the armature or inductor shaft, and is operated by it. The -Bosch circuit breaker is illustrated in Figure 50, the parts being -mounted on a plate attached to the shaft and revolving with it. The -lever is L-shaped, pivoted at the angle, with one end resting on the -tip of a screw. When the shaft revolves, the other end of the lever is -dragged over a block of metal that acts as a cam; this makes it move -on its pivot and separates it from the screw. By turning the screw the -distance of separation may be adjusted. - -[Illustration: FIG. 50.—“BOSCH” CIRCUIT BREAKER] - -In the circuit breaker of the K-W magneto it is the cam that revolves, -while the lever is stationary, as shown in Figure 51. It will be -noticed that the cam will move the lever only twice during each -revolution; the magneto can produce four sparks during a revolution, -but with this arrangement of the cam only two of them are used. - -[Illustration: FIG. 51.—“K-W” CIRCUIT BREAKER] - -It has been said that an intense sparking current is produced when -there is a great change in the strength of the magnetism, and when the -change in strength occurs suddenly. There cannot be any alteration in -the change in strength, for the greatest magnetic strength of the core -is what is given it by the magnet, and changing from this to nothing -is the greatest change possible. The suddenness with which the change -takes place, however, depends on the speed at which the magneto runs. A -4-cylinder engine requires two sparks to each revolution of the crank -shaft; the armature of a Bosch magneto for this engine will therefore -run at the same speed as the crank shaft. - -The K-W magneto, giving four sparks to the revolution, could run at -half of the speed of the crank shaft, but then the change in the -strength of the magnetism would take place slowly, and the sparking -current would not be sufficiently intense. By using only two of the -sparks the magneto is run at the same speed as the crank shaft; the -change in strength then takes place more suddenly, and a more intense -sparking current is produced. - -The circuit breaker of a magneto for a 1-cylinder engine has only one -cam, so that a single spark is produced during each revolution of the -armature; the armature makes one revolution to every two revolutions of -the crank shaft. - -However many cylinders an engine may have, the magneto must be revolved -from one point of sparking to the next in the interval between ignition -in one cylinder and ignition in the next cylinder to fire. A magneto -is driven by the crank shaft through gears or by a chain, which are so -proportioned and set that the magneto is at a point of sparking at the -instant when a piston is in position for ignition. - -A magneto for an engine with more than one cylinder is provided with -a _distributor_, which passes the sparking current to the particular -cylinder that is ready for ignition. A distributor is a revolving -switch built into the magneto, with as many _points_, or _contacts_, as -the engine has cylinders. At the instant when the magneto produces a -sparking current, the revolving distributor arm is in position to pass -the current to one of the contacts, and the current flows to the spark -plug with which it is connected. - -An electric current must have a complete path, or circuit, in order -to be able to flow. In a magneto ignition system this path is partly -of wire and partly of the metal of the engine. The diagram in Figure -45 indicates that the current returns to the magneto from the circuit -breaker lever and the spark plug by wire, but in actual construction it -returns by the metal of the engine. This is called a _ground return_; -the circuit is said to be _grounded_. - -[Illustration: FIG. 52.—“BOSCH” MAGNETO IN SECTION] - -Figure 52 is a side view of a Bosch magneto, partly broken away to -show the interior. As can be seen, one end of the primary winding is -screwed to the armature, and is thereby connected with the metal of the -magneto; as the magneto is attached to the engine the primary winding -is thus in contact with that also. The other end of the primary winding -leads to the insulated block of the circuit breaker, Figure 50. This -block is _insulated_ from the disk; that is, while it is attached to -the disk, it is kept from touching it by means of pieces of hard rubber -or mica. Through these an electric current cannot pass. - -The lever is grounded; that is, it is in contact with the metal of -the magneto. When the lever touches the screw of the insulated block, -current can flow; when they are separated, the circuit is broken. - -One end of the secondary winding, Figure 52, is attached to the outer -end of the primary. The other end leads to the _slip ring_, which is a -metal rim on a hard rubber wheel attached to the armature and revolving -with it. Sparking current flowing to the slip ring is led off by a -carbon brush and passed to the distributor. - -Should a spark plug wire fall off while the engine is running, the -current would lose its path and would seek another; it is quite -powerful enough to make a path for itself by breaking through the -windings. As this would injure the magneto, such a thing is prevented -by providing a _safety spark gap_, which acts like a safety valve in -giving the current a path when the regular path is interrupted. It -consists of two points of metal, one attached to the metal of the -magneto and the other connected with the slip ring brush; it is a more -difficult path than the one through the spark plug, but easier than -breaking down the windings. - -Figure 53 is a section of the K-W magneto. As the coil does not -revolve, no slip ring is necessary; the sparking current flows directly -to the distributor. - -[Illustration: FIG. 53.—“K-W” MAGNETO IN SECTION] - -To start an engine, the crank shaft must be turned at sufficient -speed to drive the magneto fast enough to produce a spark. With large -engines this is often a difficult matter, so it is very usual to equip -a magneto with an _impulse starter_. One part of this is attached to -the magneto shaft and the other to the engine shaft that drives the -magneto; the two are connected by a spring. When starting, a catch -holds the armature and prevents it from turning. The drive shaft -turns, however, and in so doing winds up the spring. At a certain -point the catch is automatically released, and the spring then throws -the armature over at a speed that gives a good spark. A spark is thus -assured, even though the engine is being cranked very slowly. - - - - -CHAPTER VII - -BATTERY IGNITION SYSTEMS - - -While the greater number of tractor engines use magneto ignition, many -use battery and coil systems, which are the same in general principle -as magneto systems, but produce magnetism in a different manner. - -Copper is a _nonmagnetic_ metal; that is, magnetism will not flow -through it, nor can it be magnetized. If a pile of iron filings is -stirred with a copper wire there will be no effect, as might be -expected; but if a current of electricity flows through the wire, the -iron filings will cling to it, as shown in Figure 54, as if it were a -real magnet. - -[Illustration: FIG. 54.—MAGNETISM IN A COPPER WIRE] - -It is one of the principles of electricity that when a current flows -through a wire, the wire is surrounded by magnetism, which continues as -long as the current flows; when the circuit is broken and the current -stops flowing, the magnetism dies away. The magnetism produced is -feeble and can be very greatly increased by winding the wire around an -iron bar. The magnetism produced by the current then flows into the -bar, and that, like the core of the winding of a magneto, throws out -magnetism of its own. This is indicated in Figure 55. By changing the -intensity of the electric current, or by cutting it off, the strength -of the magnetism can be made to change, and this change of strength can -produce a sparking current. - -[Illustration: FIG. 55.—MAGNETISM FROM ELECTRICITY] - -The principle employed is illustrated in Figure 56. A is a coil of -wire wound around one end of an iron bar and connected with a battery; -B is an entirely separate coil of wire wound around the other end of -the bar, with its ends separated by a short distance. By closing the -battery switch the current will be permitted to flow in coil A, and -the bar will become magnetized; the magnetism that it throws out will -be felt by coil B. When the switch is opened the current stops flowing -and the magnetism dies out of the bar; these changes in strength will -create an electric current in coil B, which will form a spark as it -passes across the space between the ends. - -[Illustration: FIG. 56.—PRINCIPLE OF SPARK COIL] - -In ignition coils, coil B is wound on top of coil A. Coil A, called the -_primary winding_, consists of a few layers of coarse wire. The more -turns of wire there are in coil B, called the _secondary winding_, the -more intense will be the current that it produces, and the intensity -is also increased by keeping the windings close to the iron core. The -secondary winding is, therefore, made of exceedingly fine wire, and has -a very great number of turns. - -To obtain a spark, a current is permitted to flow through the primary -winding to create magnetism, and the flow is then stopped to cause -the magnetism to die away. The secondary winding is affected by each -of these changes in magnetic strength. The bar loses magnetism more -rapidly than it gains it, however; it is therefore the dying out of the -magnetism that has the greater effect on the secondary winding, and -that causes it to produce a sparking current. - -To use this principle for ignition, the engine is fitted with a -revolving switch, which closes the circuit as a piston is on the -compression stroke, and then breaks the circuit at the instant when -a spark is desired. Combined with the revolving switch, or _timer_, -is a distributor like the distributor of a magneto, which passes the -sparking current to the cylinder that is ready to receive it. - -[Illustration: FIG. 57.—“ATWATER-KENT” IGNITION SYSTEM] - -To produce an intense sparking current, it is necessary to break the -circuit as abruptly as possible, in order to cause the magnetism to die -away suddenly. Figure 57 shows how this is done in the Atwater-Kent -system. - -The parts of the circuit breaker are carried on a plate, in the center -of which revolves a shaft with a notch in it. Against the side of this -shaft rests the hooked end of the sliding catch; as the notch comes -under this hooked end, the sliding catch is drawn forward, only to be -snapped back by its spring as the notch moves from under it. The lifter -is a bit of metal, pivoted at one end, with its free end lying between -the sliding catch and the flat steel spring that carries one of the -contact points. - -A, Figure 57, is a diagram of the system. B shows the position of the -parts as the notch carries the sliding catch forward, and C shows their -positions as the spring snaps the sliding catch back to its place. It -will be seen that in thus moving back it strikes the lifter, which -in turn moves the contact spring, and so closes the circuit; but the -circuit is instantly broken as the parts spring back to position. The -movement of the parts is so rapid that to the eye they seem to be -standing still. The circuit is closed only for an instant, but that -is sufficient to magnetize and demagnetize the coil, and to produce a -sparking current. - -The operation of this system depends on the very great swiftness with -which the circuit is made and broken; there is not sufficient time -for the core to get thoroughly magnetized, but such magnetism as is -produced changes strength so quickly that it gives a sufficiently -intense current to create an ignition spark. - -In other battery systems of like principle, the circuit is closed for -a long enough time to allow the core to become fully magnetized, the -circuit then being suddenly broken. In some of these systems the timer -breaks the circuit, while in others it is broken by the magnetism, -through a _vibrator_. - -A _vibrator coil_ system is illustrated in Figure 58. The timer is a -ring made of some kind of insulating material, with a plate of metal -set in it and forming one of the timer contacts. The other contact is -the revolving brush, driven by the engine; the circuit is closed when -the brush touches the metal plate. - -[Illustration: FIG. 58.—VIBRATOR COIL IGNITION SYSTEM] - -Opposite the end of the core is a flat steel spring, or _vibrator -blade_, resting against the tip of a screw; when the core is magnetized -it draws the end of the blade to it, and separates it from the screw. -The battery current flows from the timer contact to the screw, then to -the vibrator blade and to the primary winding of the coil. The core -then becomes magnetized, and draws the blade away from the screw, -which breaks the circuit; this causes the magnetism to die away, and -a sparking current is produced in the secondary winding of the coil. -The vibrator blade, no longer held down by the magnetism, springs -back against the screw; the circuit is again made, and the action is -repeated. The movement of the vibrator blade is very rapid, being some -hundreds of vibrations a second. - -[Illustration: FIG. 59.—SPARK PLUG] - -A spark plug is illustrated in Figure 59. It consists of a metal shell -screwed into the cylinder, enclosing an _insulator_ of porcelain, mica, -or some similar material. Through the insulator passes the center -electrode, which is a rod of metal, with its lower end separated by a -short distance from the shell or from a wire attached to the shell. -This separation is the gap across which the sparking current passes, -and at which the spark occurs. - -Spark plugs receive the pressure of the power stroke, and must be -strongly made in order to withstand it. A leaky spark plug will cut -down the power of the engine, just as a leaky valve will. - - - - -CHAPTER VIII - -TRANSMISSION - - -The parts of a tractor by which the power of the engine is applied -to the driving wheels are called the _transmission_, and include the -_clutch_, _the change speed gear_, the _differential_ and the _drive_. - -It has been shown that a gas engine delivers power only when it is -running at speed; it cannot run until some outside power drives it -through the inlet and compression strokes. - -The tractor cannot move until the engine is running and delivering -power, and it follows, therefore, that it must be possible to -disconnect the engine from the driving mechanism in order that it may -run independently. This is done by means of a _clutch_, which is a -device that connects two shafts, or disconnects them. - -[Illustration: FIG. 60.—INTERNAL CLUTCH] - -A clutch must be so made that when it is engaged it takes hold, not -suddenly, but gradually. If it took hold suddenly, the tractor would be -required to jump at once into full motion; this would cause a severe -straining of the parts and probable breakage. The alternative would be -the abrupt stopping of the engine, and this would also strain things. - -By making the clutch in such a way that it slips, and takes hold little -by little, the tractor starts slowly, and gradually comes up to speed; -the slipping of the clutch then ceases, and it takes hold firmly. - -All clutches operate by the friction of one surface against another; in -some, the surfaces are curved and in others flat, while in still others -the clutch is a band around a wheel, or _drum_. A clutch is operated by -a hand lever or by a foot pedal. - -Figure 60 shows a type of clutch that operates inside a drum, which is -often the overhanging rim of the flywheel. The shaft in the center is -independent of the flywheel, and it is the purpose of the clutch, which -is attached to the shaft, to lock the shaft and flywheel together when -the tractor is to be started. - -The brake shoes, which bear against the drum, form the ends of pivoted -levers, and are lined with an asbestos material that resists the heat -caused by the friction against the drum. - -A cone-shaped block of steel slides lengthways on the shaft; when it -is pushed into position, it forces out the yokes, and thus presses the -brake shoes against the drum. - -A _plate clutch_, or _disk clutch_, is shown in Figure 61. The -principle of a plate clutch may be illustrated by placing a half-dollar -between two quarters and pinching them with the thumb and forefinger. -If they are held loosely, the half-dollar may be turned between the -quarters, but if they are pinched tightly, the friction between the -coins will be so great that one cannot be turned without turning the -others. - -[Illustration: FIG. 61.—PLATE CLUTCH] - -Attached to the flywheel are studs, which support a disk, or plate; -this plate revolves with the flywheel, and is practically a part of it. -On either side of this plate are other plates that are supported on the -drive shaft; they revolve with it, but can slide along it. The end of -the shaft is square and fits a square hole in a collar, so that while -the collar may slide along the shaft, the two must turn together. Cams -are mounted on the hub of one of the plates in such a position that -they can press the outside plates together and pinch the flywheel plate -between. The cams are operated by pressing the collar against them. - -The first drawing shows the clutch out, or released; the flywheel may -then turn without turning the shaft, for the plates are not in contact. -The second drawing shows the clutch in, or engaged. The collar is -pressed against the cams, and the plates in turn are drawn together, -pinching the flywheel plate between them. The flywheel and the drive -shaft then revolve together. - -Plate clutches are often made with more than three plates; some makes -run in a bath of oil, and some are intended to work dry. - -In a cone clutch, the overhanging rim of the flywheel is funnel-shaped, -and into it fits a cone-shaped disk carried on the end of the drive -shaft. To engage the clutch, the disk is slid along the shaft against -the flywheel, the friction between the two being sufficient to drive -the shaft. - -When a clutch is thrown in it should take hold gradually, slipping at -first, but finally having a firm grip. When it is thrown out, it should -release instantly and completely. - -The power delivered by an engine depends on the _bore_ and _stroke_ -of the cylinder, and on the speed. The greater the bore, or diameter -of the cylinder, and the greater the stroke, or distance the piston -moves in a half-revolution of the crank shaft, the larger will be the -combustion space, and the larger will be the charge of mixture that -it can take in; the larger the charge, the greater will be the power -produced when the charge burns. - -Each cylinder produces power once during every two revolutions of the -crank shaft; if the engine runs at 1,000 revolutions per minute there -will be twice as many power strokes as there would be if it ran at 500 -revolutions per minute, and during that minute it will produce twice as -much power. - -A traction engine is intended to run at a certain speed, at which it -will produce its greatest power without overstraining its parts. This -_normal speed_ for any particular engine depends on the number of -cylinders, their size and design, and other details established by the -manufacturer. To get the best from the engine, this is the speed at -which it should always be run. - -The power required to move the tractor depends on various things; -the hardness and smoothness of the ground, the grade, the load it is -pulling, and so on. The tractor might be running on level ground, -pulling so great a load that the engine is called on for all of the -power that it can deliver. - -On coming to a hill, still more power will be required, for now the -tractor and its load must be lifted as well as moved forward. The -engine, already working at its limit, cannot deliver the extra power -needed, and will slow down and stop unless something is done to aid -it. In such a case, the change speed gear is used to give the engine -a greater leverage on its work, just as a block and tackle gives a -greater leverage or purchase to a man who must lift a heavy weight. - -Let us say that the normal speed of the engine is 1,000 revolutions per -minute, and that it is so connected that it makes 40 revolutions while -the driving wheels make 1, the speed of the tractor being 3 miles per -hour. If it is a 4-cylinder engine there will thus be 80 power strokes -to every revolution of the driving wheels. The engine is delivering its -full power and cannot do more should the tractor be called on for an -extra exertion, such as climbing a hill or crossing rough ground. - -By changing the connections between the engine and the driving wheels, -the engine can be made to run twice as many revolutions to one turn of -the driving wheels, which will give double the number of power strokes; -the wheels will thus be turned with twice the force. As no change is -made in the speed of the engine, the wheels will now turn at half their -former speed, and the tractor will run at 1½ miles per hour. It will, -however, have twice the ability to overcome obstacles. - -This change in the connections between the engine and the drive is -performed by the _change speed gear_, which is driven by the engine and -which in turn drives the wheels. - -There are many varieties of change speed gears, but the main principle -in them all is the same, for they depend on the action of cog-wheels, -or _gears_. - -When two gears running together, or _in mesh_, have the same number of -teeth, they will revolve at the same speed. If one has half as many -teeth as the other—10 teeth and 20, let us say—the 10-tooth gear will -make two revolutions while the 20-tooth gear is making one. - -There are two shafts in a change speed gear, one driven by the engine -and the other driving the wheels; each carries gears that mesh with -gears on the other shaft. These pairs of gears are of different sizes, -and any pair may be used; the shaft driven by the engine runs as the -engine runs, while the speed of the other shaft depends on the pair of -gears that is being used. - -By changing from one pair of gears to another, the driven shaft, and, -consequently, the wheels, may be run at a greater or less number of -revolutions, while the speed of the engine and the driving shaft do not -change. The number of power strokes that occur during one revolution of -the wheels is thus changed, and they turn with more force or with less. - -_High speed_, or _high gear_, means the combination of gears that -gives the greatest speed to the wheels, but the fewest power strokes -to each revolution. The combination that gives the slowest speed to -the wheels, but the greatest number of power strokes, is called _low -speed_, or _low gear_. - -Many tractors have but two speeds, a low and a high; but others have an -intermediate combination for conditions too severe for running on high -gear but too easy for low. - -The change speed gear mechanism also provides for reversing or backing -the tractor. Two gears running together turn in opposite directions, -while in a train of three gears the outside gears turn in the same -direction. The usual combination in a change speed gear uses two gears -for going ahead; to run the driven shaft the other way, which will make -the tractor back, a third gear is meshed between the two. - -The differences between various makes of change speed gears are in the -methods used to put into action the desired pair of gears. - -[Illustration: FIG. 62.—PRINCIPLE OF SLIDING GEAR] - -Two general plans are used. In one of them, a gear of each pair can -slide endways on its shaft, but must revolve with it; thus it can be -slid into mesh or out. In the other, the gears of a pair are always in -mesh, but one of them is loose on its shaft, so that shaft and gear can -revolve independently. To make the pair of gears operate, the loose -gear is locked to its shaft. - -Figure 62 shows the principle of the _sliding gear_ type. One part of -the shaft driven by the engine is square, and fits into square holes -in its gears, which may thus slide along it, but must revolve with it. -Each sliding gear is moved by a shifter block, which is operated by -a shift lever. There is a shifter block for each gear, and the shift -lever may be moved sideways to operate either one of them. - -Figure 63 shows the _jaw clutch_ type of change speed gear, in which -the gears are in mesh all of the time, but run loose on their shaft -when they are not working. The drawing shows _bevel gears_, which are -used when the driving and driven shafts are at a right angle. The same -principle is used for _spur gears_ on shafts that are parallel, as in -Figure 62. - -[Illustration: FIG. 63.—PRINCIPLE OF JAW CLUTCH CHANGE SPEED GEAR] - -The center of the shaft is square, and fits a block that can slide -endways, but that must revolve with it. The ends of the block have -heavy teeth that can mesh with teeth on the hubs of the loose gears; -meshing the block with one of the gears forces that gear to revolve -with the shaft. - -The drawing shows only one speed forward; the reverse is obtained by a -second gear on the same shaft, which is placed on the opposite side of -the center of the driven gear, and turns it in the opposite direction. - -When a tractor turns, the outside wheel makes a larger circle than the -inside wheel, and has a longer path to travel. Both wheels travel their -paths in the same time, so it follows that the outside wheel must move -faster than the inside wheel, although both are being driven by the -engine. This is allowed for by the _differential_, which is driven by -the change speed gear, and which in turn drives the wheels; it operates -automatically by the difference in the resistance to the rolling of the -wheels. - -The action of the differential is illustrated by an experiment that -requires a pair of wheels on an axle, like buggy wheels, and a stick -long enough to reach from one to the other. With the wheels on smooth -ground, put the ends of the stick through the wheels at the top, each -end pressing against a spoke. Hold the stick at its center and push it -forward; the stick will transmit the pressure to the spokes, and the -wheels will turn. The wheels being on smooth ground, there is equal -resistance to their movement, and they will run straight forward. - -Now repeat the experiment with the wheels so placed that one is on -a smooth roadway and the other on sand; as the wheel on the smooth -surface meets with less resistance than the other does, it moves -faster, and the pair of wheels circles, although the stick applies -equal pressure to both. - -The power developed by the engine is transmitted by the differential -to both rear wheels; when the wheels meet with equal resistance, they -turn equally, but when one wheel meets with greater resistance than the -other, it slows down, while the other speeds up to correspond. - -A tractor with two driving wheels must use a differential in order to -make turns easily. Without a differential, the wheels would run always -at equal speed, and in making a turn one would be obliged to slip. - -The use of a differential has a disadvantage, however. If one wheel -is in a mudhole and the other is on hard ground, the wheel in the mud -meets with little resistance, and all of the power of the engine goes -to it; it spins without moving the tractor, while the other wheel -remains stationary. In such a case all of the power should be applied -to the wheel that has traction in order to move the tractor, but this -the differential fails to allow. - -In some tractors the differential is so made that the parts may be -locked together. This lock is used when one wheel is in a mud hole, and -as by its use power is transmitted equally to both wheels, the tractor -moves. - -Great care must be taken to unlock the differential as soon as the need -for the lock has passed, for otherwise the wheels would slip on a turn, -and the parts of the transmission might be strained or broken. - -A differential is usually made with two bevel gears placed face to -face; between them is a frame holding three or more small bevel gears -that are in mesh with them both. The engine revolves the frame with its -small gears; each of the large bevel gears revolves a driving wheel. - -When the tractor moves straight ahead the differential turns as if it -were one solid piece. When there is less resistance to one driving -wheel than to the other, the small bevel gears, in addition to -revolving with the frame that carries them, turn on their shafts. This -transmits the power of the engine to one wheel more than the other, -according to the resistance of the wheels. - -[Illustration: FIG. 64.—“I. H. C.” CHAIN DRIVE, SHOWING THE -DIFFERENTIAL] - -Figure 64 shows one of the large bevel gears of a differential, with -the three small gears, the other large bevel gear being removed. A -differential in section is shown in Figure 65. - -A tractor with only one driving wheel has no differential. Such -tractors usually have two wheels, but one of them runs loose on -the axle, and serves only to support the tractor. The rear axle -construction of a tractor with a 1-wheel drive is shown in Figure 66, -which should be compared with the 2-wheel rear construction shown in -Figure 65. - -[Illustration: FIG. 65.—“CASE” REAR AXLE] - -There are a number of methods used for transmitting power to the -driving wheels. In Figure 64 a chain is used; there are tractors with -but one chain, and others with a chain for each driving wheel. - -[Illustration: FIG. 66.—“OIL-PULL” REAR AXLE] - -The most usual method is by a _master gear_, or _bull gear_, which is a -large and heavy gear attached to the driving wheel, as shown in Figures -65 and 66. In some tractors this gear is nearly the size of the wheel, -and is fully exposed; in others it is smaller, and enclosed in an -oil-tight housing. - -[Illustration: FIG. 67.—DRIVING WORM] - -The small gears that drive the bull gears are on the ends of the cross -shaft, called the _jack shaft_, that carries the differential. - -In the Fordson tractor the differential is built into the axle, as it -is in an automobile, and power is applied by a _worm_. The worm is -driven by the change speed gear, and is a screw meshing with a gear on -the differential, whose teeth are cut at the proper angle to make them -fit the threads of the worm. A worm, which is shown in Figure 67, is -always enclosed, and runs in oil. - - - - -CHAPTER IX - -TRACTOR ARRANGEMENT - - -The uneven ground over which tractors must work requires the weight to -be kept low, to prevent capsizing, and they are also built wide, for -the narrower they are the more easily they tip over. They cannot be -broad in front, however, for if they are the steering wheels cannot -be swung enough to permit them to turn in the small circle that is -desirable. - -To give a small turning circle some tractors are built with the front -of the frame raised enough to permit the wheels to cut under. Others -use small steering wheels, but this is not desirable because small -wheels will not run over rough ground as readily as large ones, and -steering is difficult. - -[Illustration] - -[Illustration: FIG. 68.—TRACTOR ARRANGEMENT] - -[Illustration] - -[Illustration: FIG. 69.—TRACTOR ARRANGEMENT] - -Types of tractors are indicated in Figures 68 and 69. A has a -4-cylinder vertical engine in front, driving both wheels by bull gears, -while B is a 2-cylinder horizontal engine in the center, driving both -wheels by chains. C has a 4-cylinder vertical engine set across the -frame. These three types have riveted steel frames, to which the parts -are attached. - -In D, the drive is entirely enclosed within the rear axle housing, -and the rear part of the frame is formed by the axle housing and the -housing of the change speed gear. - -E has a 1-cylinder horizontal engine with a single chain drive, while F -has a similar engine but drives to both wheels. - -G has no frame, its place being taken by the crank case of the engine -and the housings of the parts of the transmission. G and H have -4-cylinder vertical engines, G driving through an enclosed rear axle -and H through bull gears. - -[Illustration: FIG. 70.—“GRAY” TRACTOR] - -Figure 70 has one broad wheel instead of two narrower ones, this being -placed inside of the frame instead of outside. It has a 4-cylinder -vertical engine placed across the frame, and drives through two chains. - -[Illustration] - -[Illustration: FIG. 71.—TYPES OF FRONT AXLES] - -The front axle of a tractor is almost always attached to the frame by -a pivot, so that the wheels will follow uneven ground. Some of the -forms of front axles are shown in Figure 71. - -[Illustration: FIG. 72.—SPRING SUPPORT] - -The first is a plain bar, while the second is arched to raise the front -of the frame in order to permit the steering wheels to cut under. In -the third the wheel axles are mounted on springs, which take up some of -the vibration and act as shock absorbers. - -The fourth axle shown is built of steel bars riveted together to form -a truss, and the fifth is similar, with the frame pivot carried on -springs. The sketches at the bottom indicate the extent to which the -pivoted front axle may swing. - -Figure 72 shows a spring support for the axles, front and rear. -The axle bearing is in a block sliding in guides, the weight being -supported by a heavy spring. - - - - -CHAPTER X - -LUBRICATION - - -The most important thing in the care of a tractor is to oil it; every -moving part should be lubricated, and the greatest care should be taken -to assure a never-failing supply of oil and grease. - -Carelessness in lubrication is the principal cause of tractor trouble. -There is nothing complicated or difficult about keeping a tractor -properly oiled; yet more tractors break down from careless lubrication -than from any other cause. Every tractor-maker issues an oiling diagram -and oiling instructions, and there is no excuse for an operator whose -machine does not get the right kind of lubricant in the right quantity -at each place where lubrication is necessary. - -The cause of wear is friction; oil reduces friction and so reduces -wear. No matter how smooth and highly polished two pieces of steel may -be, there will be friction between them if they are rubbed together, -and they will wear each other. If they are oiled, the particles of oil -will keep the pieces from touching each other, and there will be no -wear. - -Other substances than oil can be used; there are some kinds of -machinery that are lubricated with water, for instance. For general -use, however, oil and grease are the best, and are practically always -used. - -The object of a lubricant is to keep two pieces of metal from touching; -it must therefore be able to get between them, and must stay there. If -the pieces are large and heavy, there will be much greater pressure -on the oil than if they are small and light, and the oil must be able -to withstand this pressure and resist being squeezed out. The oil -that would keep the small, light pieces apart might not be able to -stand the pressure of a greater weight, and might be squeezed out from -between two heavy pieces. - -Oil has a tendency to cling to whatever it touches, and thick oil -or grease has more of this tendency than a thin, or “runny” oil. If -a thick oil or grease is used on light machinery, such as a sewing -machine, this clinging tendency would make the machine run hard, and -might even prevent its operation. - -When oil is heated, it becomes thinner, or more “runny.” Through -this, an oil used in a hot place might get so thin that it would not -lubricate; and on the other hand, an oil that works all right in the -heat of summer might get so thick on a cold winter day as to be useless. - -A slow-moving part of a machine uses a thick oil or a grease; a thin -oil must be used for a part that moves at high speed. - -Some of the parts of a tractor move slowly and some at high speed; some -are cool and some are hot. Different kinds of lubricants are therefore -required, and it is a grave mistake to use a lubricant that is not -suitable to the work that it is required to do. - -The engine is the most difficult part of a tractor to lubricate, and -the part that suffers most if the supply fails or if the wrong kind -of lubricant is used. In the first place, it is so hot that any oil -will burn, being turned to carbon; the best that can be expected of -an oil is that it will resist burning until it has done its work of -lubricating the piston and cylinder. - -A tractor engine is more difficult to oil than an automobile or -truck engine for the reason that it works harder and more steadily. -An automobile engine is rarely driven to the limit of its power; it -has frequent opportunities to cool when running down hill. A tractor -engine, on the other hand, works at its full power all day long with -no opportunities to cool off. An oil that gives good satisfaction on -an automobile might ruin a tractor engine through its inability to -withstand the greater heat. - -The makers of tractors understand the importance of using proper oils, -and recommend certain brands and grades; these recommendations should -be followed in order to get the best possible results. All makers -specify at least two kinds of lubricants, and most of them three; one -specifies six, which range from a light sewing machine oil to a grease -so thick that it is nearly solid. Whatever the recommendations may be, -they should be followed. - -In general, lubricants are classified according to their thickness, and -they range from the light oil used for typewriters and sewing machines -to grease so thick that it may be cut like butter. The thinnest oil -is used for the circuit breaker pivot; this part is usually moved in -one direction by a cam and in the other by a light spring. A thick oil -would gum the bearing to such an extent that the spring might not be -able to move the lever. - -[Illustration: FIG. 73.—“MOGUL” OILING DIAGRAM] - - ----+----------------------+----------------------------+----------- - KEY | DESCRIPTION | QUANTITY |LUBRICATION - ----+----------------------+----------------------------+----------- - ONCE EVERY HOUR - ----+----------------------+----------------------------+----------- - L | Rear axle bearing | Two complete turns | Cup Grease - ----+----------------------+----------------------------+----------- - ONCE EVERY TWO HOURS - ----+----------------------+----------------------------+----------- - A | Differential hub | One complete turn | Cup Grease - B | Rear wheel hub | One complete turn | Cup Grease - C | Differential pinion | One complete turn | Cup Grease - H | Front wheel hub | Two complete turns | Cup Grease - T | Governor and cam | Two complete turns | Cup Grease - | shaft bearing | | - ----+----------------------+----------------------------+----------- - TWICE EVERY DAY - ----+----------------------+----------------------------+----------- - E | Governor | Oil | Cylinder - | | | oil - F | Outboard bearing | Two complete turns when | Cup Grease - | grease cups | plowing | - G | Transmission | One pint | See note - | | | below - |{ Magneto trip | Grease every 5 hours | Cup Grease - N |{ Magneto roller and | Oil every 5 hours | Oil - |{ slide | | - J | Steering worm | Keep covered | Cup Grease - W | Steering hub grease | One complete turn | Cup Grease - | cups | | - V | Steering worm shaft | Oil every 5 hours | - R | Lubricator eccentric | Oil every 5 hours (keep | - | | wool in pocket) | - P | Cam roller slide | Oil every 5 hours | - K | Valve levers | Fill with oil every 5 hours| - | | (keep wool in pockets) | - ----+----------------------+----------------------------+----------- - ONCE EVERY DAY TRACTOR IS IN USE - ----+----------------------+----------------------------+----------- - U | Steering sector shaft| One complete turn | Cup Grease - ----+----------------------+----------------------------+----------- - D | MECHANICAL LUBRICATOR - | Fill with a good grade of heavy gas engine cylinder oil. - | Turn the crank on the mechanical oiler 40 to 50 times when - | starting the engine. - | IMPORTANT - | In cool or cold weather the oil in lubricator tank must be - | warmed as it will not flow readily unless of the right - | temperature. - ----+--------------------------------------------------------------- - G | TRANSMISSION - | In warm weather, use heavy oil such as “600” transmission - | or Polarine transmission oil; in cold weather, use a good - | light oil. - S | GOVERNOR - | Cylinder oil in governor should cover shoe. - M | MAGNETO - | Oil magneto bearings once a week with sewing machine or - | cream separator oil. - ----+--------------------------------------------------------------- - -The oil used in an engine is thicker, and has a high _burning point_ -and high _viscosity_; that is, it should be able to resist burning, and -should not get so thin when it is heated that it will be squeezed out -of the bearings. The same kind of oil that is used in the engine can be -used in many other parts of the tractor. - -Grease is usually used for the gears of the transmission and drive. -There is very great pressure between the teeth of two meshing gears, -and only thick oil and grease have sufficient viscosity to resist being -squeezed out. - -The thickest grease is used on the tracks of caterpillar-type tractors. - -Before operating a tractor, the lubrication chart supplied by the -manufacturer should be studied with great care, and all of its -requirements should be observed. This chart is usually in the form of -a diagram accompanied by a table, as shown in Figure 73, which is the -lubrication chart of one of the International Harvester tractors. This -figure illustrates the constant attention that is demanded by this most -important part of tractor operation. - -[Illustration: FIG. 74.—“ILLINOIS” OILING DIAGRAM] - - -The table calls for four lubricants, these being sewing machine oil, -which is very thin and liquid; gas engine cylinder oil; transmission -oil, which is as thick as molasses; and cup grease, which is like -butter. - -The engine is oiled automatically, the only requirements being to keep -the oil tank filled, and to be sure that the oiler is working. The -other parts of the tractor are oiled or greased by hand. - -Figure 74 is the oiling chart of the Illinois tractor. - -There are three systems used for engine lubrication: _splash_, _force -feed_, and by a mechanical oiler. In the splash system, a pool of oil -is maintained in the crank case, of such a depth that the ends of the -connecting rods just dip into it. They strike it with sufficient force -to splash it to all parts of the crank case, the oil that strikes the -pistons being carried up into the cylinders and lubricating the walls. - -The end of the connecting rod is often fitted with a dipper, as shown -in Figure 75, to strike into the oil, as well as an oil catcher, -shown in the same drawing, which is a little trough that catches the -splashing oil and guides it to the connecting rod bearing. - -[Illustration: FIG. 75.—END OF “TWIN CITY” CONNECTING ROD] - -To oil the wrist pin bearing there is an oil groove around the piston -that collects oil from the cylinder walls; a hole connects this groove -with the hollow wrist pin, from which other oil holes lead to the -bearing. This is shown in Figure 76. - -[Illustration: FIG. 76.—WRIST PIN LUBRICATION] - -In the force feed system a pump driven by the engine forces oil through -pipes and channels to all of the bearing surfaces. Oil collects in a -pocket in the crank case, called the _sump_, and is drawn from it by -the pump. The sump is usually provided with a wire mesh strainer that -separates out any dirt. - -[Illustration: FIG. 77.—FORCE FEED OILING SYSTEM OF “GRAY” ENGINE] - -From the oil pump the oil is forced to the bearings by pipes and by -holes drilled in the crank shaft and other parts, as shown in Figure 77. - -[Illustration: FIG. 78.—OIL PUMP] - -An oil pump is illustrated in Figure 78. It consists of a plunger -driven by the engine, working in a cylinder provided with two ball -check valves, one for inlet and the other for outlet. On an upward -stroke of the plunger the cylinder fills with oil, which is forced to -the engine bearings by the following inward stroke. - -[Illustration: FIG. 79.—“E.B.” OIL PUMP] - -Figure 79 shows a similar pump with a strainer over the intake, the -outlet being through the holes L in the pipe H. In the pump illustrated -in Figure 80 the plunger is hollow, and fills with oil during an -inward stroke; the oil is forced out to a passage around the plunger, -and passes to the bearings by the holes H. - -[Illustration: FIG. 80.—OIL PUMP WITH HOLLOW PLUNGER] - -Figure 81 shows two methods of preventing oil from leaking out around -the plunger. In the first of these, a channel is formed in the upper -part of the pump cylinder, leading to the crank case; any oil that -leaks past the plunger flows to the crank case by this drain pipe and -is not wasted. In the second method a packing of soft material, such -as cotton or asbestos, is placed around the plunger, and is pressed -against it by a _gland_, which is like a thick washer. A _packing nut_ -screws against the gland, and thus squeezes the packing against the -plunger. - -[Illustration: FIG. 81.—METHODS OF PREVENTING OIL LEAKS] - -[Illustration: FIG. 82.—“TITAN” LUBRICATOR] - -A _mechanical lubricator_, or _oiler_, consists of several small oil -pumps placed in an oil tank, each pump feeding one special bearing, -and all driven by the engine. Figure 82 is a top view of a 2-cylinder -horizontal engine oiled by a six-feed oiler. The bearings that it -oils are the two ends of the crank shaft, the two ends of the cam -shaft, and the two cylinders; the gears and other bearings are oiled -by splash. An oiler is adjustable, so that it will feed any desired -quantity of oil. - -[Illustration: FIG. 83.—“I.H.C.” METHOD OF OILING CRANK PINS] - -Figure 83 shows a side view and an end view of the crank shaft of a -2-cylinder horizontal engine. To each end of the crank is attached a -ring, B, formed into a channel; oil splashing into this ring is thrown -into the channel by centrifugal force, and flows by holes, A, to the -crank pin bearings. - -The oil forced to the cylinders from the oiler, Figure 82, reaches the -wrist pin by grooves and holes, A, Figure 83. - -A 6-feed oiler is also shown in Figure 84. - -[Illustration: FIG. 84.—“HART-PARR” OILING SYSTEM] - -[Illustration: FIG. 85.—OIL CUP] - -[Illustration] - -[Illustration] - -[Illustration: FIG. 86.—PROPER USE OF A GREASE CUP] - -Figure 85 is an _oil cup_, which is used to feed an individual bearing. -It is a glass cup holding oil with an opening at the bottom into which -fits a needle valve. When the engine is at rest, the needle valve -handle at the top is turned down, which allows a spring to close the -needle valve; on starting the engine the needle valve is raised, and -the oil flows out by gravity. The dripping oil may be seen through a -sight glass at the bottom. - -In the force feed and oiler systems the oil feeds only when the engine -is running, but with an oil cup the oil feeds all of the time that the -needle valve is raised. Care must therefore be taken to turn on the oil -cup when starting the engine, and to turn it off when the engine is -stopped. - -Change speed gears and differentials are usually enclosed in oil-tight -housings that contain a supply of oil or grease. The only attention -that is required is to see that they have the necessary amount, and -that the lubricant is of the right kind. - -[Illustration: FIG. 87.—“TITAN” 10-20 OILING DIAGRAM] - -[Illustration: FIG. 88.—“INTERNATIONAL” OILING DIAGRAM] - -The bearings of wheels and of many other parts of a tractor are -lubricated with grease fed by _grease cups_; a grease cup has a cover -that, when screwed down, forces the grease out of a hole in the bottom -of the cup. In using a grease cup it is not sufficient simply to give -the cover a turn or two; the cover should be screwed down enough to -force an ample supply of grease to the bearing. This is illustrated in -Figure 86. - -Figures 87 and 88 are oiling diagrams. They show the many points at -which a tractor must be lubricated, and it should be remembered that -the failure to maintain a plentiful supply of lubricant at any one of -these points will mean the wear and breakdown of that particular part. - - - - -CHAPTER XI - -TRACTOR OPERATION - - -Before running a new tractor it should be given a careful examination -to make sure that all nuts and bolts are tight, and not secured only -by paint; that all grease cups are in position and filled; that all -parts of the mechanism are properly lubricated; that oil holes are free -from grit, and that nothing is cracked, broken or missing. It should be -cleaned of cinders and mud that may have collected in shipment, and in -general it should be seen to be in proper condition. - -A tractor, like any other piece of machinery, requires breaking in, and -for the first few days it should be run slowly and with light loads. -All parts should be plentifully oiled, for there will be rough and -uneven places on the bearings that must be worn smooth, and without oil -these would heat and be injured. - -A continual watch should be kept for loose nuts and bolts, which should -be tightened without delay. Readjustments of the clutch and brake will -be found necessary, for their linings when new may be lumpy; as these -lumps wear down through use the clutch or brake will begin to slip and -must be tightened. When the linings are worn in, this trouble will -disappear, and readjustments will be necessary only at considerable -intervals. - -Special care should be taken to keep the filler caps of the fuel and -oil tanks clean and free from dirt. If these are dirty, the dirt will -be carried into the tank when filling, and will sooner or later cause -trouble. - -The vent holes in the filler caps should be kept clear. If they are -plugged with dirt, air cannot enter the tank to take the place of the -fuel that flows out, and the feed of fuel will stop. - -Beginning when the tractor is new, a system of daily inspection should -be started, and should be continued for the working season. Big trouble -starts with small trouble, and if small trouble is cured without delay, -big trouble will be avoided. Trouble usually begins with looseness, -which may be due to a slack nut or bolt, or may come with wear. If the -loose part is not tightened, it will begin to shift its position; it -will wear, and will rapidly lead to a breakdown. - -Every day, without fail, all parts of the tractor should be inspected -for loose nuts, bolts, pipe and electrical connections, petcocks, drain -plugs, steering connections, etc. This is also the time for wiping off -the working parts, and cleaning mud and grit from rods, shafts, joints, -and other places at which dirt could make its way into bearings. - -The change speed gears of a tractor should not be shifted while in -motion, this being one of the differences between a tractor and an -automobile. In the sliding gear type of change speed mechanism, the -gears slide into mesh sideways, a tooth of one being opposite a space -between two teeth of the other. If the gears are not in the right -position for this, one tooth will strike another, and the gears cannot -be meshed. In such a case the clutch is let in for a slight touch to -move one gear, not for a dozen or twenty revolutions, but enough to -bring a space between two teeth of one gear opposite a tooth of the -other. - -If an attempt is made to shift the gears while they are in motion, the -result will be that one will grind against the other, and there will be -rapid wear and probable breakage. It is because gears cannot be shifted -while they are moving that manufacturers instruct users not to attempt -to shift on a hill without first blocking the wheels. The reason for -this is that the brakes may not hold the tractor, and if the gears are -pulled out of mesh, the machine may start to run down hill; as another -speed cannot then be engaged because the gears are moving, there will -be no control over the tractor. - -Never coast down hill; always run with one of the speeds engaged. By -switching off the ignition the motion of the tractor will drive the -engine, and this provides the best possible brake. On low gear, the -engine will turn in the neighborhood of eighty revolutions to one turn -of the driving wheels, and the work required to do this will check the -tractor on the steepest of practicable grades. - -A tractor is not built for as accurate and delicate steering as an -automobile and should always be slowed in making a turn; this is -especially true when hauling plows or other loads in the field. It is -difficult to control the tractor if a turn is made at high speed, and -the machine is liable to tip over. - -In steering and in engaging the clutch, the action should not be jerky -and abrupt, but gradual and smooth. Letting in the clutch suddenly will -start the tractor with a jerk that will strain it from end to end, and -an abrupt swing of the steering wheel will have the same effect. Making -these motions smoothly and steadily will cause the tractor to change -its direction or pace with the least possible strain and effort. This, -of course, increases the tractor’s life. - -In much of the work done by the tractor, the varying conditions of -field and soil make a continual change in the load, and the tractor -must be handled accordingly. The change from an uphill to a downhill -haul, and from sand or light loam to gumbo, will require the gears -to be shifted in order that the engine may neither labor nor race in -keeping the outfit at its work. - -There should be no hesitation in coming down to low speed when the -engine shows by its laboring that the effort of working on high gear is -becoming too great. The engine cannot deliver its full power unless its -speed is maintained, and low gear is provided for those times when the -load is too great to be handled on high. Use high speed whenever it is -possible, but trying to force the tractor to run on high with too great -a load will lead to a breakdown. - -High speed should be used for light work or for moving from place -to place, but the engine should never be run at a greater number of -revolutions than that specified by the manufacturers. It is very poor -policy to run the tractor fast over rough roads, as the pounding will -inevitably injure it. - -Cold weather changes conditions in the handling and operation of a -tractor; there is difficulty in starting, lubrication is likely to be -faulty, and there is danger of breakage in engine, radiator, and air -washer through freezing. - -Difficulty in starting comes from the use of the usual medium grade -of gasoline, which is satisfactory in mild weather, but will not -vaporize at low temperatures. Cold gasoline will not vaporize in a cold -engine; to form a mixture it is necessary to use high test gasoline, -which will vaporize at low temperatures, or to warm the engine to a -temperature at which medium grade gasoline will vaporize. - -It is advisable to keep on hand a few gallons of high test gasoline to -use in starting, or even a mixture of high test gasoline and ether, -half-and-half, for extreme cold weather. - -The engine may be warmed by pouring a bucket of hot water into the -cooling system, cranking the engine to get it into the water jackets of -the cylinders. Another plan is to wrap cloth around the intake manifold -and carburetor, soaking it with hot water, being careful not to get -water into the air intake. - -A drop of liquid gasoline on the points of the spark plug will -short-circuit them and prevent the formation of a spark; the points -should be dry, and it is an advantage to heat the plugs, screwing them -hot into the engine at the last moment before trying to start. - -Kerosene is thicker when cold than when warm; it will not flow so -freely, and the needle valve of the carburetor must be opened more in -winter than in summer to obtain a proper mixture. - -Lubricating oil also thickens in cold weather, and flows much more -sluggishly. The lubrication adjustments that are correct for summer -will therefore be incorrect for winter. This may be provided for to -a great extent by using a thinner oil in winter than the oil used in -summer. A cold snap is likely to result in burned bearings if the -change in lubrication that it brings is not allowed for. - -Grease thickens in cold weather more than oil does, and some kinds -freeze solid. In winter a light, soft grease should be used, and the -grease cups should be turned down several more turns than is usual when -the weather is warm. - -While antifreezing compounds can be used in the cooling systems of -automobiles, they are not suitable for tractors because the greater -and more continuous heat quickly evaporates them. The danger of -freezing is very great, and must be avoided; the water in the radiator -and jackets is in thin sheets, and will freeze when a bucket of water -standing in the open will not show any signs of ice. - -The only real protection against freezing is to drain out all the -water whenever the tractor is to stand idle for a sufficient time for -it to cool off. Petcocks are provided for this at the lowest points -of the system, and also in the pump when forced circulation is used. -The freezing of even a small pocket of water will be enough to crack a -cast-iron water jacket wall, and the best assurance that the system is -thoroughly drained is to open the drain cocks while the engine is still -running, shutting down as the flow stops. - -When putting up a tractor for the winter it should be thoroughly -protected from rust and corrosion. The last time that the tanks are -filled a quart of light oil should be added for every five gallons of -gasoline or kerosene; as the tank empties this will leave a coating of -oil on the inside walls. - -Fuel tanks and water system should be drained, and particular care -should be taken that all the water is out; the drain cocks should be -left open. A mechanical oiler should be filled full, to protect the -steel parts of the pumps from rust. - -A half pint of thick oil should be put into each cylinder, and spread -to the cylinder and piston walls by cranking for a few turns. Oil -should be run between the valves and their seats. - -All exterior parts should be protected by a coat of thick oil or -by paint. The governor rod, push rods, and similar parts should be -especially looked after. It is advisable to take off the magneto and -store it in a safe, dry place; spark plugs should be left in position. - -The tractor should be covered with a tarpaulin and stored in a tight -shed. - -When going over a tractor preparatory to laying it up, a list should -be made of all parts that need renewal. These parts should be procured -at once; they are more readily obtained during the winter than in the -operating season, and will be on hand for the spring overhaul. - - - - -CHAPTER XII - -ENGINE MAINTENANCE - - -FUEL SYSTEM AND CARBURETOR - -The operation of a carburetor depends on so many things that no exact -instructions for its adjustment can be given. The best that can be done -is to give a general idea of the requirements, and to outline a plan by -which the adjustment can be arrived at. - -The many makes and designs of carburetors and vaporizers that are -used on tractors have different kinds of adjustments; on most of them -the only adjustment is the needle valve that controls the fuel, but -some also have adjustable air valves. In any case, the manufacturer’s -instruction book should be studied for the understanding of the -particular carburetor in question. - -The first step in adjusting a carburetor is to get the engine running. -The needle valve should be closed, and then opened enough to give a -mixture on which the engine will start; on many carburetors this will -be about one and one half turns. The engine should then be _primed_; -that is, a little gasoline should be put in the cylinder, which may be -done with a squirt can. - -When the engine is running, and is well heated, the needle valve should -be gradually closed until the engine begins to miss, and to send jets -of flame out of the carburetor, or little explosions occur in the -carburetor. These are signs of a thin mixture, and the needle valve -should be gradually opened to make the mixture richer. The engine will -run more steadily, and will pick up speed until the mixture becomes too -rich, when it will choke and black smoke will come out of the exhaust. - -The positions of the needle valve for a mixture that is too thin and -one that is too rich have thus been found, and it remains to set it at -that point between at which the engine runs most steadily and at the -best speed. - -With adjustable air valves it is usual to adjust for idling, that is, -the slowest speed at which the engine will run steadily without load, -and then to make any necessary additional adjustment for full speed and -power. - -If a carburetor cannot be adjusted by following the usual methods, -trouble may be looked for, and this may be in the carburetor itself, -in the fuel supply, or in the intake manifold, taking for granted, of -course, that the engine is in proper condition and that the ignition -system is operating correctly. - -Dirt under the float valve will prevent the valve from seating, and the -level in the float chamber will be too high, so that the mixture is -too rich. Lifting the valve from its seat will let fuel rush through, -and loose particles will thus be washed away. If dirt is ground into -the valve and seat, or if these parts are worn, the valve must be -reseated, which is done by turning the valve against its seat with -light pressure, the end of the valve being gently tapped with a light -hammer. Under no conditions use a grinding compound, for the particles -would become imbedded in the soft metal and would ruin the valve. - -Other causes of flooding are a bent valve, the sticking of the float -pivot, and the soaking of fuel into the cork float, which is thereby -made too heavy to float properly. The remedy is to dry it, and then to -give it three coats of shellac. - -A frequent cause of trouble is dirt in the pipe from the tank to the -carburetor. While there may not be enough dirt to prevent the engine -from running slowly, it is sufficient to prevent the flow of sufficient -fuel for full power. A strainer is always provided, and this should be -drained every day; if this is not done frequently, dirt will work its -way through. - -A grain of sand in the spray nozzle will choke it, and every precaution -should be taken to keep this from happening, as well as the other -troubles that dirt brings. The best precaution is to strain the fuel -through chamois leather, or, if this is not obtainable, through a very -fine metal wire screen. - -In fuel systems that use a pump, the sticking of the check valves, and -the leaking of the pump through poor packing, will cut down the supply -of fuel. - -If air can leak into the carburetor or intake manifold, the proportions -of the mixture will be altered. To test for leaks, run the engine, and -with a squirt can squirt gasoline on the joints or other places that -are suspected of leaking air. If there is a leak, the gasoline can be -seen being sucked in. - -Air must enter the tank to take the place of the fuel that flows out, -and this is provided for by a small hole drilled in the tank-filling -cap. If this hole becomes stopped up, the fuel will not flow, and the -engine will come to a stop. There is a similar hole in the top of the -float bowl of most carburetors, and this also must be kept open. - -An engine is always started on gasoline, for that will form a mixture -when it is cold. Before switching to kerosene the engine must be hot, -and this will take several minutes of running on gasoline. - -With a double carburetor, which has a separate fuel bowl and spray -nozzle for each fuel, nothing more is required than the switching -of one or the other into action; when the two parts have once been -adjusted, they require no further adjustment. Carburetors that use -the same spray nozzle for both gasoline and kerosene will require a -readjustment when the switch is made, for, as kerosene is thicker than -gasoline, it will require a larger opening for a sufficient quantity -to pass. This readjustment is a slight opening of the needle valve on -switching to kerosene, and an equal closing when gasoline is again -used. - -A few minutes before the engine is stopped the carburetor should be -switched from kerosene to gasoline, so that when it is shut down the -fuel bowl will contain gasoline and the cylinders gasoline mixture. -This is done to make it possible to start the engine. If the engine is -stopped on kerosene, it cannot be started if it has had time to cool. -In such a case the fuel bowl must be drained of kerosene and filled -with gasoline, and the engine must be cranked until the cylinders -receive a clean gasoline mixture. - -When an engine is working at full power on kerosene, it gets much -hotter than would be the case with a gasoline mixture. Carbon particles -in the cylinder, and projecting bits of metal, such as thin spark plug -points or the edge of a screw thread, become so hot that they glow, -with the result that they ignite the incoming fresh charge and cause -preignition. The effect of this is to cause a pounding or knocking -that is very noticeable. It is then necessary to use water, which is -provided for in the carburetor. - -Water has the effect of cooling the intensely heated parts, and only -enough should be used to prevent preignition. When the knocking is -heard, water should gradually be turned on, using no more than is -necessary to stop the noise. Too much water will cause the engine to -miss by collecting on the spark plug points, thereby preventing the -passing of the ignition spark. - -Hard water should not be used, for it will form scale, which will -interfere with the action of the carburetor. Only soft water should be -used, and preferably rain water. - -Whenever the engine is stopped, the fuel valve at the tank should be -closed to shut off the carburetor supply. If this is not done, the -float valve will be the only thing that prevents the fuel from running -out, and should the float valve leak, the fuel will be wasted. - - -MAGNETO AND IGNITION SYSTEM - -A magneto that is kept clean and properly oiled rarely gives trouble, -and it is a mistake to blame it whenever the engine runs irregularly or -will not start. Its adjustments should be changed only when the other -parts of the engine have been proved to be in good condition. - -The working parts of a magneto are enclosed, and practically proof -against dust. It should be wiped off frequently, and dust and grit -should not be allowed to collect around the oil holes, for otherwise it -will work into the bearings and damage them. - -Dust and dirt are especially injurious to the circuit breaker, which -should be frequently inspected and cleaned. Very little oil should be -used on it, and this should be the light oil used for typewriters and -sewing machines. A thicker oil will become gummy, and will prevent the -free action of the lever. - -If there is much sparking at the platinum points, so that they become -corroded and rough, it is an indication that the condenser of the -magneto is not operating as it should, for the object of the condenser -is to prevent such sparking. The only remedy is to renew the condenser. - -Rough points will spark more than smooth ones; should they get into -this condition, they should be lightly filed with a file of the cut -known as “dead smooth.” If this file cannot be obtained, pinch a strip -of the finest sand paper—not emery paper—between the points, and draw -it gently back and forth, smoothing down first one point and then the -other. In smoothing platinum points the greatest care should be taken -to make them flat and true to each other. - -After smoothing the points they should be readjusted so that when they -are separated by the cam they are from ¹/₃₂ to ¹/₆₄ inch apart. - -A distributor made with a carbon brush that slides across the contacts -will require wiping off at least once a month. Carbon dust will rub off -the brush and collect on the face of the distributor; in the course of -time this will cause a short-circuit. The distributor is always made so -that it can easily be cleaned. - -A magneto is timed to an engine so that when the spark control is fully -retarded, the circuit breaker points are just separating as a piston -goes over top center. The engine is cranked until one of the pistons -is at top center; the magneto should be in position, but its coupling -should be loose, so that the armature can be revolved. The spark -control is retarded; that is, it is moved as far as possible in the -direction in which the armature turns. The armature is then revolved -in the direction in which it will be driven by the engine until it is -seen that the contact points are beginning to separate; holding the -armature, the coupling is then made fast. - -It will now be found that the distributor brush is touching one of -the contacts; that contact is to be connected with the spark plug of -the cylinder that is at top center of the compression stroke. The -following distributor contacts are connected to the remaining spark -plugs in the order in which their cylinders fire. - -Should the magneto be suspected of being out of order, the first test -is to disconnect a wire from its spark plug, and support the tip ⅛ inch -from the metal of the engine while the engine is cranked briskly; if a -spark appears, it is evidence that the magneto is operating and that -the trouble is elsewhere. - -If there is no spark, repeat the test with the switch wire disconnected -from the magneto. This wire and the switch form a circuit from the -metal of the engine to the insulated part of the circuit breaker; -when the switch is closed, or in the “off” position, this circuit is -completed, and as the magneto current flows over it instead of over -the regular sparking circuit, no spark is produced at the plug. It -sometimes happens that the switch or wire is defective, and allows the -current to take that circuit even when the switch is in the open or -“run” position. If this is the case it will be shown by a spark on -cranking the engine with the switch wire disconnected at the magneto, -and no spark when it is connected. - -If the switch and wire are all right, examine the circuit breaker to -see whether the contact points are clean, and that they touch when the -cam allows them to; touch the circuit breaker lever to see that it is -free to move and that its spring is not broken. In some tractors the -magneto is in such a position that the circuit breaker cannot easily -be seen; in such a case hold a small mirror in front of the circuit -breaker and examine the reflection. - -If the circuit breaker is in good condition, examine the distributor to -see whether it is dirty, or the brush broken; if these parts are all -right, the trouble is of such a character as requires the magneto to be -returned for repair. - -Ignition trouble is usually in the spark plugs. The insulator cracks -easily in many makes, which will permit the current to leak across -without forming a spark; it is frequently the case that the crack does -not show, and the best test is to replace the suspected plug with a -plug that is known to be good. If the cylinder fires with one plug and -not with the other, there is no question as to the cause of the trouble. - -The insulator of the plug must be kept clean, for a deposit of carbon -on it will form a path by which the current can pass without forming -a spark. A dirty plug can best be cleaned by brushing it with a stiff -toothbrush dipped in gasoline. A carbon deposit can be softened by -soaking the plug in gasoline for a few hours, and can then be brushed -off more easily. - -The spark gap of a plug should be from ¹/₃₂ to ¹/₆₄ inch. After -considerable use the points will be burned off, and the gap will become -too wide; the points should then be bent to form a proper gap. - -Oil and grease will rot rubber, and the ignition wires should -therefore be wiped clean. Oil-soaked cables will give trouble, and -should be replaced with new ones. - -It is frequently difficult to locate a leakage of current. If the -engine is misfiring and losing power, and a leakage of current through -poor insulation is suspected, the easiest way to detect it is to run -the engine in the dark. Leaks will show themselves by sparks, which are -then easily seen. - - -COMPRESSION - -In order to deliver its full power a gas engine must have good -compression, and compression should frequently be tested by cranking -the engine slowly and steadily with the ignition switched off. If -compression is good, there will be a springy, elastic resistance -that becomes greater as a piston approaches the end of a compression -stroke, and that throws the piston outward as dead center is passed. -Compression should be the same for all cylinders. - -If there is a leakage of compression, the only resistance will be from -the bearings, and it will be the same for all parts of the stroke. - -A compression leak often makes a hissing noise that can be distinctly -heard, and by which it can be located, but more often it makes no -sound, and its location must be found by testing. The leak may be at -any of the openings into the combustion space; at the valves, around -the spark plugs or piston rings, or at the cylinder head gasket. - -To discover whether the gasket leaks, run gasoline along the line of -the gasket joint with a squirt can while the engine is being cranked -briskly; at a leaky place it will be sucked in or blown out. The same -test should be made around the spark plug. - -The remedy is to reset the cylinder head, using a new gasket, and being -sure that the surfaces are clean and free from grit. - -Piston ring leaks are usually caused by the rings sticking in their -grooves through the formation of carbon. To test for piston ring -leaks, pour a half pint of cylinder oil into each cylinder, and crank -the engine slowly. The oil will form a seal around the pistons, and if -compression is then improved, the rings are shown to be at fault. - -To free the rings, pour a few tablespoonfuls of kerosene into each -cylinder, and spread it by giving the engine a few turns; after -standing for an hour or so the carbon should be sufficiently softened -to free the rings. - -If the leakage of compression is due to the rings being worn and loose -in their grooves, they must be replaced. - -The most usual cause of compression loss is leaking valves. With its -continual pounding against its seat, and the heat to which it is -exposed, a valve and its seat will become rough and pitted, and will -leak; when in this condition the valve must be ground. - -A valve is ground by spreading grinding compound on the seat, and -turning the valve against it. This requires the valve spring to be -taken off; the exact method of doing this depends on how these parts -are made. - -If the valves are in a removable cylinder head, valve grinding is most -easily done by taking the cylinder head to a bench. In many designs the -valve seats are part of the cylinder casting, and the job is done on -the tractor. - -In grinding a valve the valve is not turned around in one direction -only, for this would cut grooves in the valve and seat. To obtain -smooth surfaces the valve should be given part of a turn in one -direction, and then turned equally in the other direction; after every -few turns the valve should be lifted and dropped to another position on -the seat. In this way the grinding is made even all around. - -[Illustration: FIG. 89.—GRINDING VALVE IN ENGINE WITH FIXED HEAD] - -The best tool for valve grinding is a carpenter’s brace with a screw -driver blade fitting the slot in the valve, as shown in Figure 89. -This drawing illustrates a cylinder with a fixed head; the valve is -reached by unscrewing the plug from the opening directly above it. When -grinding valves in an engine of this design the opening between the -valve pocket and the combustion space should be plugged with a rag or -waste to prevent the grinding compound from getting into the cylinder. - -With the valve grinding tool in position, swing the handle back and -forth ten or twelve times; then lift the valve, place it in a new -position, and repeat. The valve is lifted most easily by a light spring -placed under the valve disk, as shown in Figure 89. - -From time to time the valve disk and seat should be cleaned off and -examined to see whether they are smooth and free from pits and scores. -If they appear to be, make marks around the valve disk with a lead -pencil, replace the valve, and give it a complete turn. If this wipes -off the pencil marks all around the valve, the grinding is complete, -and the valve may be replaced with its spring and spring retainer. It -is not necessary to grind until the entire thickness of the valve disk -and seat are smooth; a narrow band all around will make the valve tight. - -After grinding, and before replacing the valve, all traces of the -grinding compound should be wiped off, and great care taken that none -of it gets into the cylinder, valve stem guide, or other working part. - -[Illustration: FIG. 90.—GRINDING VALVE IN DETACHABLE HEAD] - -On an engine with a removable head containing the valves, the head -may be taken to a work bench, which makes grinding easier. This is -illustrated in Figure 90. On an engine in which the valve and its seat -may be taken out, the seat may be clamped in a vise, as shown in Figure -91. With valves of either of these types, the grinding may be tested by -turning the head or the seat so that the disk is down, and pouring in -gasoline. If the valve is not tight, the gasoline will leak through, -and grinding must be continued. - -[Illustration: FIG. 91.—GRINDING VALVE IN DETACHABLE SEAT] - -When a valve seat is very badly worn it must be redressed, which is -done with a cutting tool to be obtained from the maker of the tractor, -and illustrated in Figure 92. This has a stem fitting the valve stem -guide which centers the tool and assures a true cut. If a seat is so -worn as to need redressing, the valve will be in such bad condition -that it must be discarded and a new one used. This must be ground in -before the engine is run. - -Grinding a valve lowers it in its seat, and usually makes it necessary -to readjust the push rod. When an engine is cold there is a space of -about ¹/₃₂ inch somewhere between the cam and the valve stem; in Figure -93, this space is shown to be between the valve stem and the rocker -arm. As the engine heats up the valve stem lengthens, and this space -permits it to do so. - -[Illustration: FIG. 92.—VALVE SEAT CUTTER] - -If the space is too small, the stem will come against the rocker arm -or the push rod, and the valve will be held off its seat, causing -a compression leak. If the space is too great, the valve will open -too late and close too early. The space must therefore be carefully -adjusted, and this is arranged for on practically all makes of tractor -engines. - -[Illustration: FIG. 93.—“HOLT” VALVE ARRANGEMENT] - -One-thirty-second of an inch is the thickness of a 10-cent piece; it -should just be possible to slip a slightly worn dime into the space -when the engine is cold. - - -VALVE TIMING - -By _timing the valves_ is meant the setting of the cam shaft in such a -position that the valves are opened at the correct point in the stroke. -It is necessary to time the valves only when the cam shaft has been -taken out and must be replaced. The principle of valve timing should be -understood, however, in order to be able to tell whether an engine is -timed correctly. - -It will usually be found that the face of the flywheel bears letters -and figures that are indicators of the timing of the valves. This -arrangement on the E-B engines is shown in Figure 94. Two lines are -cut in the face of the flywheel, one marked ex. cl. 1-4, which means -exhaust valve closes, cylinders 1 and 4, and the other marked CENTER -1-4, to indicate that the pistons in those cylinders are on center. A -straight-edge is held against the finished surface of the housing and -the crank shaft is turned to bring one of the marks in line with it; at -that point the valves or pistons are as indicated by the lettering. - -[Illustration: FIG. 94.—VALVE TIMING, USING MARKS ON FLYWHEEL] - -[Illustration: FIG. 95.—VALVE TIMING] - -The flywheel is also marked with a dot to indicate the firing point. -When the dot is in line with the straight-edge, ignition should occur -with the spark control fully advanced. - -Figure 95 shows the valve arrangement of the same engine, with the -exhaust valve just closing; the point of the cam has passed under the -lifter or push rod, and has permitted the valve to come to its seat, -but is still holding the lifter against the valve stem. - -To check the valve setting, hold a slip of tissue paper, such as a -cigarette paper, in the space between the lifter and the valve stem, -while the engine is cranked slowly. While the cam is holding the valve -off its seat the paper will be pinched between the lifter and the valve -stem and held firmly. At the instant when the paper is freed and can -be moved, the valve is seated and the point of the cam is just passing -from under; the proper mark on the flywheel should then be in line with -the straight-edge. - -As the cams for all valves are in one piece with the cam shaft, setting -one valve sets them all and checking the setting of one checks the -setting of all. - -Before taking out a cam shaft, two adjoining teeth of its gear should -be marked with a prick punch or a small cold chisel, and a similar mark -should be made on the tooth of the crank shaft gear that comes between -them. In replacing the cam shaft it is then necessary only to return -the teeth to the same position. Timing gears are usually marked in this -way by the manufacturers. - - -CARBON - -A kerosene lamp that is turned too high gives a dense black smoke that -is composed of fine particles of carbon. A piece of paper held in the -smoke is quickly covered with a deposit of carbon, commonly called -soot, or lamp-black. - -All fuel oils and lubricating oils contain carbon. When these oils -burn in the cylinder, they produce carbon, much of which passes out -of the exhaust, while the rest deposits on the valves and on all parts -of the combustion space. This deposit hardens, and eventually makes -trouble through causing preignition. - -The deposit is rough, and the heat in the cylinder is sufficient to -make the outstanding particles glow; they ignite the incoming charge, -and cause preignition. The sign of carbon trouble is a sharp knocking -in the cylinder, especially when the engine is under a heavy load. The -sound is the same as that caused by too great an advance of the spark. - -Carbon deposit can be greatly reduced by pouring a few tablespoonfuls -of kerosene into each cylinder and cranking for a few turns to spread -it to all parts of the combustion space. This will soften the carbon -and much of it will be blown out when the engine is next started. Best -results will be obtained if the kerosene is poured in after a run, when -the engine is hot. - -If the carbon deposit is too hard to be softened by kerosene, it can -be removed by scraping. This requires the cylinder head to be taken -off, when the deposit can be scraped and chipped with a screwdriver. -Care should be taken to keep the carbon crumbs from getting into the -cylinders, valve stem guides, or other places where it would cause wear. - -In taking off the cylinder head the gasket should be handled carefully, -and protected from denting and bending. A battered or bent gasket is a -sure cause of compression leaks. In replacing a metal gasket, give it a -coat of cylinder oil on both sides to improve its seating. - -When replacing the cylinder head, set all of the bolts up a little at -a time, instead of screwing some of them tight while others are loose. -One bolt drawn tight may tilt the cylinder head slightly, and there -will be a distortion when another bolt is tightened. This is avoided by -setting up all of the bolts a little at a time. - -Running on too rich a mixture, giving the engine too much oil, and not -using an air cleaner in dusty work will carbonize an engine rapidly. -Blue smoke at the exhaust is a sign that too much lubricating oil is -being used; black smoke indicates too rich a mixture. Carbonizing -can be greatly reduced by careful adjustment of the lubricator and -carburetor. - - - - -CHAPTER XIII - -LOCATING TROUBLE - - -There are many ways in which an engine can give trouble, but these are -not serious to an operator who understands the action of an engine, -and who works with his brain as well as with his hands. Each of these -troubles has a distinct cause; proper care will avoid them, but if they -come the reasons for them can be determined by simple tests. - -In order to develop full power, an engine must be in good mechanical -condition; that is, the bearings must be free without being loose, -the gears must run well, the pistons and their rings must not bind or -be too free, and so on. It must be properly lubricated and cooled, -compression must be correct, it must get a good mixture, and ignition -must take place at the right time. If an engine gives trouble, it is -because one of these systems is not working properly, and it is not at -all difficult to locate the cause and to correct it. - -If an engine gets a good mixture, which is ignited properly, it will -run; if it will not give any explosions it is because one or the other -of these systems is not working properly. An inspection or a simple -test will show which one is at fault. - - -ENGINE WILL NOT START - -If an engine will not start after being cranked a dozen or twenty -times, it is useless to continue to crank it. It is not getting either -a proper mixture or an ignition spark, and it saves time and energy to -find out where the trouble is, rather than to keep on cranking in the -hope that something may happen. - -When a tractor engine refuses to start, the trouble is usually with the -mixture, and, more often than not, this is due to carelessness or to -forgetfulness. The tank may be empty, or the fuel valve may be closed, -so that the carburetor is dry; see if there is fuel in the carburetor -bowl. The engine may have been shut down while running on kerosene, -instead of having been switched to gasoline for the last few minutes of -its run, so that the carburetor, intake manifold and cylinders contain -kerosene, which will not vaporize without heat, instead of gasoline, -which will. In this case the engine must be primed with gasoline. - -If too much gasoline has been used for priming, the cylinders may -contain a mixture that is too rich to ignite; the engine should then be -cranked briskly with the fuel shut off and the compression relief cocks -open, to clear out the rich mixture and fill the cylinders with air. - -Water in the fuel will make starting difficult or impossible. It is -easy to forget to shut off the water valve of the carburetor when -stopping the engine, and when starting, water from this valve will -prevent the forming of a mixture and will also interfere with the -ignition. - -If the mixture is apparently all right, the fault may be in the -ignition. A drop of liquid fuel or of water, for instance, may be on -the spark plug points; this will short-circuit them and no spark will -be formed, although the sparking current is passing. - -If there is a suspicion that the ignition system is at fault, and that -the magneto is not producing a sparking current, it should be tested, -as explained in Chapter XII. - -Starting in cold weather is always more difficult than starting when it -is warm. Helps in cold weather starting are given in Chapter XI. - -A leaky inlet manifold will admit an extra amount of air that will -completely alter the proportions of a mixture. Thus the mixture will -be wrong, although the carburetor adjustment seems to be correct. -Manifold leaks are usually at the joints, but occasionally a manifold -is found with a hole in it due to poor casting or material, or a crack -may develop. - -Difficulty in starting due to poor compression caused by stuck valves -or rings will show its cause by the ease with which the engine can be -cranked. - -If an engine is free enough to turn over, poor lubrication or cooling -will not interfere with starting it. Faults in these systems show -themselves only when an engine is running. - - -ENGINE LOSES POWER - -An engine will lose power through a defect of compression, carburetion, -ignition, cooling or lubrication, or because of a mechanical fault. - -If the trouble comes from cooling or lubrication, the engine will -overheat and thus make the cause known. A bearing that binds will -become very hot, while if the cooling system fails, the engine will be -hot all over. When the engine is excessively hot, the pistons will -expand, and much of the power of the engine will be used up in forcing -them to move. - -An engine that is not hotter than usual, and is having regular and even -explosions, probably loses power through a loss of compression. This is -the most usual cause of this trouble, and it is located and remedied as -explained in Chapter XII. - -If compression is good, the loss of power may be due to a clogged -muffler or exhaust pipe, which will not permit the free escape of the -burned gases. This condition will prevent full charges of fresh mixture -from entering the cylinders, and the engine then cannot be expected to -deliver full power. - -Another possible cause of a loss of power with the engine apparently in -proper condition is the sticking or poor adjustment of the governor. -The factory adjustment of the governor should not be changed, however, -until it is definitely proved that that is where the trouble lies. - -If the engine misses fire, or runs irregularly, the loss of power -will be due to faulty carburetion or ignition. The mixture may be -too rich or too lean; in either case the trouble will be remedied by -readjusting the carburetor. A mixture that is very much too lean will -make itself known by _backfiring_; there will be little explosions at -the carburetor. This should be remedied at once, for the danger of -fire from it is very great. Black smoke at the exhaust is a sign of a -mixture that is too rich. - -An engine will not deliver full power if it is run on a retarded -spark. A loss of power from this cause will be accompanied by general -overheating of the engine. - - -ENGINE STOPS - -The manner in which an engine stops will indicate the reason for it. - -A failure of the ignition system that stops the formation of current, -like the sticking of the circuit breaker lever, will cut off all -explosions instantly; the engine will stop abruptly. An engine will not -stop abruptly from any fault with the mixture; with mixture trouble the -explosions will become weaker and weaker until they cease. - -If an engine stops through a failure of the lubrication or cooling -systems it will be intensely hot, which will not be the case if the -fault is with carburetion or ignition. - -A running engine will not be brought to a stop by a loss of compression. - - -ENGINE MISSES - -A steady or irregular miss in one cylinder is usually due to the spark -plug’s being cracked or dirty. Carburetor trouble will affect all the -cylinders; it cannot affect one cylinder only, and missing in one -cylinder may be put down as ignition trouble. In this case ignition -trouble does not mean magneto trouble, for if the magneto produces -sparking current for one cylinder it will produce it for all. Therefore -ignition trouble in only one cylinder is in those parts of the -ignition system supplying that cylinder; that is, in the spark plug or -in the spark plug cable. - -A less likely cause for missing in one cylinder only is poor -compression. It is usually the case that if compression is poor in one -cylinder it is poor in them all, but a broken valve or piston ring or a -weak valve spring will weaken compression in one and not in the others. - -A cylinder that misses is cooler than the others, and can be located by -feeling. It can also be located by short-circuiting the spark plugs one -at a time; this will make no difference in the dead cylinder, but when -the spark plug of an active cylinder is short-circuited the speed of -the engine will drop. - -To short-circuit a spark plug, take a wooden-handled screwdriver or -other tool and rest the blade on the engine near the spark plug; then -tilt until its shank is close to the spark plug terminal. The spark -current will then pass to the metal of the engine by way of the tool -instead of by the spark plug points. This is also a test of ignition, -for a spark will pass between the terminal and the tool. - -Irregular missing in all cylinders may be due to a fault at one of -the parts of the ignition system that supplies them all; a dirty -distributor, for instance, or a sticking circuit breaker lever, or -rough platinum points. It may also be due to a clogged fuel line, which -prevents the carburetor from getting a regular and sufficient flow. - -Irregular missing will also be caused by loose ignition connections, -and by loose switch parts. - - -ENGINE STARTS; BUT STOPS - -When an engine starts readily but quickly slows down and stops, the -reason is almost always an insufficient supply of fuel. An obstruction -in the pipe may prevent the fuel from flowing fast enough to keep the -carburetor bowl filled when the engine is running; when the engine -starts, the fuel is sucked out of the spray nozzle faster than it comes -in through the float valve, so the carburetor is soon drained and the -engine stops. The bowl then fills, only to be sucked dry again when the -engine is next started. - -This difficulty is caused by dirt in the fuel, which collects in the -strainer or the fuel pipe. The strainer is so arranged that it may be -easily drained and cleaned; to clear out the pipe, shut off the fuel at -the tank, disconnect the pipe at both ends, and blow through it. - -The strainer should be drained every day; it is sufficient to open the -strainer drain cock for two or three seconds. - -Most of the troubles due to dirt in the fuel will be avoided if the -fuel is strained when filling the tank. - -Another thing that will bring an engine to a stop is the clogging of -the vent holes in the tank filler cap and in the top of the carburetor -bowl. These holes should be clear, so that air can enter to replace -the fuel that is used; if air cannot enter the fuel will not flow, and -the tank is then said to be _air-bound_. - - -ENGINE OVERHEATS - -An engine may overheat either because it produces more heat than the -cooling system can take care of, or because the cooling system is not -taking off all of the heat that it should. - -Running an engine with the spark retarded will cause it to overheat; so -will a failure of the lubrication and an obstruction to the passage of -the exhaust gases. - -If an engine has been taken down and overheats when it is reassembled, -it may be that the magneto has been wrongly timed, and produces its -spark too late. If an engine has been running properly but begins to -overheat, the ignition cause will be the faulty setting of the spark -control, or the slipping of the spark control rod. - -When an engine is run on kerosene, the oil in the crankcase must be -frequently drained off and replaced with fresh oil. The reason for -this is that part of the kerosene that goes to the cylinders does not -vaporize and burn, but works its way past the pistons and into the -crankcase, where it thins the lubricating oil. As the oil thins, it -loses its ability to lubricate, and the engine begins to overheat. - -Anything that produces extra friction will cause overheating, as, for -example, a wrist pin that works endways and rubs against the cylinder -wall, or a tight bearing. - -For a cooling system to work properly it must contain a full supply of -water, the passages must be clear, sufficient air must pass through the -radiator, and the pump must be in proper condition. - -Hose connections will rot, and a strip of rubber may peel off the -inside and be drawn across the passage; or if dirty water is used, the -dirt may choke the fine radiator passages or other channels. If the -radiator is covered with mud, air cannot get at the tubes to take the -heat from the water that they contain. - -A very usual cause of overheating is a slipping fan belt; an adjustment -is provided by which the belt can be tightened when it works loose. - - -ENGINE SMOKES - -Black smoke indicates that the mixture is too rich; blue smoke is a -sign of too plentiful lubrication. Oil that is too thin, or that is -of a poor grade, will cause smoking; good quality oil of the grade -recommended by the manufacturer should always be used. - -Broken piston rings, or rings stuck in their grooves, will be the cause -of smoking because they will permit an excess of oil to pass by them. - - - - -CHAPTER XIV - -CAUSES OF TROUBLE - - - Engine will not start. No mixture. - No ignition. - No compression. - - Engine starts, Clogged fuel pipe or strainer. - but will not Air-bound tank or carburetor. - continue running. Clogged exhaust. - Wet spark plugs. - Governor out of adjustment. - - Engine loses power. Retarded spark. - Poor compression. - Overheating. - Clogged exhaust. - Incorrect mixture. - Governor out of adjustment. - Tight bearings. - Dragging brake. - Slipping clutch. - Overloaded. - - Engine stops suddenly. Ignition trouble. - - Engine slows down Clogged fuel supply. - and stops. Incorrect mixture. - Overheated. - - Regular miss in one - cylinder. Defective spark plug or wire. - - Irregular miss in all Sticking contact breaker. - cylinders. Defective distributor. - Clogged fuel line. - Irregular fuel feed. - Water in fuel. - Faulty ignition connections. - - Engine runs unevenly. Incorrect spark plug gap. - Incorrect mixture. - Binding carburetor float. - Sticking valves. - Sticking governor. - - Engine overheats. Spark retarded. - Faulty cooling. - Faulty lubrication. - - Engine smokes. Black smoke; mixture too rich. - Blue smoke; too much oil. - Broken or stuck piston rings. - Poor oil. - - Engine backfires Mixture too lean. - through carburetor. Sticking inlet valve or weak - inlet valve spring. - - Explosions in exhaust Missing spark. - pipe. Mixture too rich. - Sticking exhaust valve. - - - - -INDEX - - - Adjusting a carburetor, 213 - Advance of ignition; theory of, 18 - Air cleaner or washer, 71 - Air inlet; extra, 63 - Armature, 106 - Atwater-Kent ignition system, 136 - Automatic carburetor, 63 - Automobiles and tractors compared, 1 - Axles; types of front, 172 - - Backfire, 55 - Balance weights, 31 - Bearings, 31 - Bosch magneto; theory of, 110 - Bosch magneto circuit, 111 - Bosch magneto windings, 110 - Bull gear drive, 165 - Burning point of oil, 182 - - Cam, 39 - Carbon; formation of, 56 - Carbonization, 56 - Carbon; removing, 242 - Carburetor, 57 - Carburetor action, 60 - Carburetor adjustment, 213 - Carburetor adjustment for two fuels, 218 - Carburetor; compensating, 63 - Carburetor connections, 89 - Carburetor; description of, 72 - Carburetor; float feed, 76 - Carburetor; heating the, 70 - Carburetor; parts of, 70 - Carburetor; pump feed, 80 - Carburetor; stopping on gasoline, 218 - Carburetor strainer, 89 - Carburetor; trouble with, 215 - Carburetor; using water in, 219 - Causes of trouble, 259 - Centrifugal force, 94 - Change speed gear; action of, 152 - Change speed gear; jaw clutch, 156 - Change speed gear; purpose of, 6 - Change speed gear; shifting, 203 - Change speed gear; sliding, 154 - Change speed gear; theory of, 149 - Choke, 67 - Circuit; Bosch magneto, 111 - Circuit breaker; magneto, 110 - Cleaner; air, 91 - Clutch; action of, 144 - Clutch; expanding, 145 - Clutch; how to use, 205 - Clutch; plate or disk, 146 - Clutch; purpose of, 6 - Cold weather care of tractor, 207 - Cold weather starting, 207 - Combustion space, 11 - Combustion; theory of, 52 - Compression; importance of, 16 - Compression leaks; locating, 228 - Compression stroke, 16 - Compression; testing the, 227 - Connecting rod, 35 - Cooling system, 46 - Crank shaft, 30 - Cycle; gas engine, 11 - - Dead strokes, 12 - Differential; action of, 161 - Differential; purpose of, 7 - Differential; theory of, 158 - Dirt in the fuel, 215 - Disk clutch, 146 - Distributor; magneto, 124 - Dixie magneto action, 119 - Double bowl carburetor; adjustment of, 218 - Double opposed engine, 25 - Drive; master gear or bull gear, 165 - Drive; purpose of, 6 - Drive; worm, 166 - - Engine base, 30 - Engine; double opposed, 25 - Engine; horizontal, 25 - Engine; how power is delivered by, 21 - Engine loses power, 249 - Engine misses, 252 - Engine overheats, 256 - Engine; priming, 214 - Engine; principle of, 9 - Engine; purpose of, 6 - Engine smokes, 258 - Engine starts; but stops, 254 - Engine stops, 251 - Engine trouble; locating, 246 - Engine; vertical, 25 - Engine will not start, 246 - Exhaust stroke, 20 - Exhaust valve, 38 - Expanding clutch, 145 - Extra air inlet, 63 - - Firing order, 28 - Float feed carburetor, 76 - Force feed oiling system, 186 - Frame; purpose of, 8 - Freezing; to prevent, 209 - Front axles; types of, 172 - Fuel; dirt in the, 215 - Fuel; straining the, 89 - - Gas engine cycle, 11 - Gasket, 30 - Gasoline mixture, 57 - Governor, 94 - Grease cup, 197 - Grease; when used, 182 - Grinding valves, 229 - Grounded circuit or ground return, 125 - - Heat; action of, 9 - Heat; effect on oil of, 177 - Heat necessary in forming mixture, 58 - Heating the carburetor, 70 - Heating the mixture, 86 - Horizontal engine, 25 - - Ignition point; changing the, 103 - Ignition system; Atwater-Kent, 136 - Ignition system; parts of, 105 - Ignition; theory of, 17, 102 - Impulse starter, 128 - Induction and induced current, 106 - Inductor magneto, 115 - Inlet stroke, 14 - Inlet valve, 38 - - Jack shaft, 165 - Jaw clutch change speed gear, 156 - - K-W magneto action, 115 - Kerosene mixture, 57 - - Leaks of compression; locating, 228 - Lean mixture, 54 - Loading, 67 - Lubricating systems, 184 - Lubrication chart; use of, 182 - Lubrication; importance of, 175 - - Magnetism, 105 - Magnet; poles of, 106 - Magneto action; Bosch, 110 - Magneto action; Dixie, 119 - Magneto action; K-W, 115 - Magneto distributor, 124 - Magneto distributor; cleaning, 222 - Magneto inductor, 115 - Magneto; oiling a, 221 - Magneto platinum points; care of, 221 - Magneto safety spark gap, 127 - Magneto spark; theory of, 105 - Magneto; theory of Bosch, 110 - Magneto timer or circuit breaker, 110 - Magneto timing, 223 - Magneto trouble; testing for, 224 - Manifold, 70 - Master gear drive, 165 - Mechanical oiler, 192 - Mixer, 57 - Mixing chamber, 70 - Mixture changes with engine speed, 62 - Mixture; formation of, 53 - Mixture; gasoline and kerosene, 57 - Mixture; heating the, 86 - Mixture; heat necessary to form, 58 - Mixture; rich, 55 - Mixture; theory of, 9 - Mixture; thin, or lean, 54 - - Oil affected by heat, 177 - Oil; burning point and viscosity, 182 - Oil cup, 193 - Oiler; mechanical, 192 - Oiling chart; use of, 182 - Oiling; importance of, 175 - Oiling systems, 184 - Oil pump, 188 - Oil; varieties used on tractors, 179 - - Piston, 34 - Piston pin, 34 - Piston rings, 37 - Piston rings; care of, 228 - Plate clutch, 146 - Poles of magnet, 106 - Power diagram, 21 - Power production, 12 - Power stroke, 19 - Preignition, 56, 83, 104 - Priming the engine, 214 - Pump feed carburetor, 80 - Push rod, 42 - Push rod adjustment, 234 - - Radiator, 48 - Retard of ignition; theory of, 19 - Rich mixture, 55 - Rocker arm, 42 - - Safety spark gap, 127 - Shuttle armature, 107 - Sliding change speed gear, 154 - Spark coil; principle of, 133 - Spark coil; vibrator, 138 - Spark coil; windings of, 134 - Spark plug, 140 - Spark plug gap, 226 - Spark plugs; trouble with, 225 - Splash oiling system, 184 - Spray nozzle, 57 - Spring support, 173 - Starter; impulse, 128 - Starting in cold weather, 207 - Starting the engine; theory of, 13 - Steering gear; purpose of, 7 - Steering; instruction in, 205 - Storing a tractor, 210 - Straining the fuel, 89 - Strangler, 69 - - Tappet, 42 - Tappet adjustment, 234 - Temperature; effect of changes on mixture, 66 - Testing for magneto trouble, 224 - Testing the compression, 227 - Theory of gas engine, 9 - Thermo-syphon cooling system, 48 - Thin mixture, 54 - Throttle, 68 - Throws of crank shaft, 30 - Timer; magneto, 110, 121, 122 - Timing a magneto, 223 - Timing the valves, 237 - Tractor; caring for in cold weather, 207 - Tractor; difficulties in oiling, 178 - Tractor driving, 205 - Tractor; handling a new, 201 - Tractor inspection, 203 - Tractors and automobiles compared, 1 - Tractor; storing, 210 - Tractor types, 167 - Transmission; parts of, 143 - Trouble; causes of, 259 - Trouble; locating, 246 - - Valve; exhaust, 38 - Valve grinding, 229 - Valve; inlet, 38 - Valve mechanism, 42 - Valve operation, 39 - Valve seat; redressing, 234 - Valve timing, 237 - Vertical engine, 25 - Vibrator coil, 138 - Viscosity of oil, 182 - - Washer; air, 91 - Water added to mixture, 58, 83, 219 - Water jackets, 48 - Windings; Bosch magneto, 110 - Windings of spark coil, 134 - Worm drive, 166 - Wrist pin, 34 - -*** END OF THE PROJECT GUTENBERG EBOOK TRACTOR PRINCIPLES *** - -Updated editions will replace the previous one--the old editions will -be renamed. - -Creating the works from print editions not protected by U.S. copyright -law means that no one owns a United States copyright in these works, -so the Foundation (and you!) can copy and distribute it in the -United States without permission and without paying copyright -royalties. 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