Types of Lubricating Systems

1. Splash system

2. Forced feed system

Splash Lubrication

Splash lubrication is a method of applying lubricant, a compound that reduces friction, to parts of a machine. In the splash lubrication of an engine, dippers on the connecting-rod bearing caps are submerged in oil with every rotation. When the dippers emerge from the oil trough, the oil is splashed onto the cylinders and pistons, lubricating them.

Experts agree that splash lubrication is suitable for small engines such as those used in lawnmowers and outboard boat motors, but not for automobile engines. This is because the amount of oil in the trough has a dramatic impact on how well the engine parts can be lubricated. If there is not enough oil, the amount splashed onto the machinery will be insufficient. Too much oil will cause excessive lubrication, which can also cause problems.

Engines are often lubricated through a combination of splash lubrication and force feeding. In some cases, an oil pump keeps the trough full so that the engine bearings can always splash enough oil onto the other parts of the engine. As the engine speeds up, so does the oil pump, producing a stream of lubricant powerful enough to coat the dippers directly and ensure a sufficient splash. In other cases, the oil pump directs oil to the bearings. Holes drilled in the bearings allow it to flow to the crankshaft and connecting rod bearings, lubricating them in the process.

Combination Splash and Force Feed

In a combination splash and force feed, oil is delivered to some parts by means of splashing and other parts through oil passages under pressure from the oil pump. The oil from the pump enters the oil galleries. From the oil galleries, it flows to the main bearings and camshaft bearings. The main bearings have oil-feed holes or grooves that feed oil into drilled passages in the crankshaft.

The oil flows through these passages to the connecting rod bearings. From there, on some engines, it flows through holes drilled in the connecting rods to the piston-pin bearings. Cylinder walls are lubricated by splashing oil thrown off from the connecting-rod bearings. Some engines use small troughs under each connecting rod that are kept full by small nozzles which deliver oil under pressure from the oil pump. These oil nozzles deliver an increasingly heavy stream as speed increases. At very high speeds these oil streams are powerful enough to strike the dippers directly. This causes a much heavier splash so that adequate lubrication of the pistons and the connecting-rod bearings is provided at higher speeds. If a combination system is used on an overhead valve engine, the upper valve train is lubricated by pressure from the pump.

Force-Feed

A somewhat more complete pressurization of lubrication is achieved in the forcefeed lubrication system. Oil is forced by the oil pump from the crankcase to the main bearings and the camshaft bearings. Unlike the combination system the connecting-rod bearings are also fed oil under pressure from the pump. Oil passages are drilled in the crankshaft to lead oil to the connecting-rod bearings. The passages deliver oil from the main bearing journals to the rod bearing journals.

In some engines, these opening are holes that line up once for every crankshaft revolution. In other engines, there are annular grooves in the main bearings through which oil can feed constantly into the hole in the crankshaft. The pressurized oil that lubricates the connecting-rod bearings goes on to lubricate the pistons and walls by squirting out through strategically drilled holes. This lubrication system is used in virtually all engines that are equipped with semi floating piston pins.

 Full Force Feed

In a full force-feed lubrication system, the main bearings, rod bearings, camshaft bearings, and the complete valve mechanism are lubricated by oil under pressure. In addition, the full force-feed lubrication system provides lubrication under pressure to the pistons and the piston pins.

This is accomplished by holes drilled the length of the connecting rod, creating an oil passage from the connecting rod bearing to the piston pin bearing. This passage not only feeds the piston pin bearings but also provides lubrication for the pistons and cylinder walls. This system is used in virtually all engines that are equipped with full-floating piston pins.

Need of Lubrication System

Lubrication is the admittance of oil between two surfaces having relative motion. The objects of lubrication may be one or more of the following:

1. To reduce motion between the parts having relative motion.

2. To reduce wear of the moving part.

3. To cool the surfaces by carrying away heat generated due to friction.

4. To seal a space adjoining the surfaces.

5. To absorb shocks between bearings and other parts and consequently reduce noise.

6. To remove dirt and grit that might have crept between the rubbing parts.