Roger B. Whitman

“ 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. ”

“ 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 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. ”

“ 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 [Pg 246] 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. ”

“ 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 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. ”

“ 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. ”

“ 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. ”

“ 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. ”

“ 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. ”

“ 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. ”

“ 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 ”

“ 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. ”

“ The design of a carburetor is a complicated matter, because the [Pg 66] 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. ”

“ 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 [Pg 247] forgetfulness. The tank may be empty, or the fuel valve may be closed, so that the carburetor is dry ”

“ 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 [Pg 252] 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. ”

“ 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. ”

“ 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. ”

“ 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. ”

“ 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. ”

“ 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. ”

“ 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. ”

“ 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 ”

“ 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 [Pg 207] 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. ”

“ 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. ”

“ 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. ”

“ 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 ”