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.