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]