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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.