Roger B. Whitman

“ It is obvious that in order to obtain a current of the greatest strength the conductor by which it flows must present the least possible resistance, and for this reason copper is used almost universally to convey the current from one place to another. A copper wire will carry safely a current that would heat an iron wire of the same size to the melting point. The resistance of a small conductor is much greater than that of a large one, so that the size of a conductor must always be considered in relation to the current that is to be conveyed. ”

“ 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. ”

“ The defects of two-cylinder vertical engines with either design of crank shaft outweigh any possible advantage of that construction, and the horizontal double-opposed type, in evenly occurring power strokes, mechanical balance, and simplicity, is in almost universal use for cars of low power.
A two-cylinder engine does not require so heavy a fly wheel as a one-cylinder engine in proportion to the power delivered, because there is a power stroke every revolution instead of in alternate revolutions, and the parts must be carried over only one dead stroke instead of three. ”

“ 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. ”

“ A magneto is a machine that when driven generates an electric current, and is in almost universal use for this system of ignition. In many cars the system is so arranged that the driver has his choice between ignition by battery and coil, as described, and ignition by magneto, but the mechanical production of a current is so reliable that many automobile builders rely on the magneto alone. ”

“ To understand the action of the differential, imagine the rear wheels of a car to be jacked up clear of the ground so that they are free to revolve, and the housing to be revolved by hand. As it turns, the driving wheels will turn also, for the resistance to each is the same, and the pinions, being in mesh with both bevel gears, cannot revolve on their studs. If one of the wheels is now held stationary and the housing revolved, the bevel pinions will revolve on their studs, and roll around on the stationary gear ”

“ 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. ”

“ IGNITION The charge of explosive mixture in the combustion space is ignited, or set on fire, by an electric spark, and the apparatus for producing and controlling this spark is called the ignition system. It is with this part of the mechanism of an automobile that a novice has the greatest difficulty, for an electric current is usually regarded as being surrounded by an air of mystery. ”

“ 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 battery is exhausted, or nearly so, it will not magnetize the core of the coil sufficiently to induce a current that will give a strong enough spark to ignite the mixture. The length of time that a battery should last, or the mileage that it should give, is learned from experience, and when it is exhausted in less time there is evidence that it has either been short-circuited or that the current has been used too extravagantly. ”

“ 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 development of the gasoline automobile at home and abroad has produced a great variety of designs, good, bad, and indifferent, but the advancement of the industry has weeded out the unsatisfactory and improved the good until with few exceptions the leading makes show a striking similarity in all but details. ”

“ 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 the four-cycle type of engine, which is in almost universal use for automobiles, the events are considered with reference to the movement made by the piston during which they are performed, and may be called the inlet, compression-combustion, power, and exhaust strokes. In order that the engine may continue to run, it is obvious that the events must be performed in the correct order, and that the failure of one will affect all the others. ”

“ 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 ”

“ 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. ”

“ It is most inadvisable to take a magneto to pieces without an exact knowledge of its construction. Except for lubricating the bearings, it is best to leave it entirely alone. In setting a magneto, it must be remembered that it is not delivering current continuously, and that when the iron core of the armature is parallel to the poles of the magnets no current is produced. ”

“ 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. ”

“ The type of engine that will give satisfaction depends on the work that is demanded of it, the care that it will receive, and the knowledge of the operator. A one-cylinder engine, having a minimum of parts, may be successfully managed by a novice, but its vibration, and the fact that it delivers power for only one fourth of the time that it runs, make it unsatisfactory for any but light work. ”

“ 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. ”

“ A grounded circuit requires careful insulation of the lead wire, for as it is very likely to come into contact with the metal of the engine, a break in the insulation would permit the current to leak and to return to the generator without doing its work, this condition being called a short circuit. Grounding the circuit saves wire and reduces complication; simplicity is important in automobile work, and a reduction of the parts much to be desired. ”