The Lubrication System

During operation, the movable engine components slide or roll over stationary ones. The rubbing surfaces of the engine components, despite their being machined to a high degree of finish, have irregularities or asperities. The surface irregularities of the working parts in rubbing contact interlock or cohere, so that the friction force opposing the relative motions of the parts is increased, thus reducing the engine power. Dry friction is attended by increased heating and accelerated wear of the working parts. To reduce friction and, at the same time, cool the parts, a film of lubricating oil is introduced between the rubbing surfaces of the parts. The oil film keeps the surfaces apart, thereby providing a condition of fluid friction instead of dry friction. With fluid friction, there is no direct contact between the surfaces of parts in relative motion, hence friction losses in the film of oil are much smaller than those generated by dry friction, and wear of the parts is greatly reduced.

The purpose of the engine lubrication system is to supply oil continuously to the rubbing engine parts and remove heat from them.

ENGINE OILS. The working parts of automotive engines are lubricated with high-quality engine oils. These oils must possess an optimum viscosity, high lubricity, or oiliness, good antricorrosive properties, and high stability. To improve the service properties of engine oils, they are treated with special additives.

Viscosity is a very important characteristic of engine oils, for it determines their ability to flow. An oil with excessively high viscosity is very thick, and it is difficult for it to penetrate the clearances between the rubbing engine parts, while an oil with too low viscosity flows easily and does not stay in the clearances. In both cases, wear on the rubbing surfaces of the working parts is intensified and the engine power is reduced. Oil gets thicker as it becomes colder. Therefore, oils with a viscosity of 10 mm²/s are usually used in summer and those 8 mm²/s in viscosity, in winter. It is essential that the oil used should strictly comply with the particular engine specifications and the season.

The reliable operation of engines largely depends on the purity of the engine oils used. The oils must be free from mechanical impurities and water. These contaminants get into the oils mainly during shipment, reception, dispensing, and storage. Crankcase oils are especially prone to contamination with mechanical impurities where the engines are run in conditions of the ambient air heavily laden with dust. Therefore, when handling engine oils every measure must be taken to prevent their being contaminated with mechanical impurities and water.

ENGINE LUBRICATION SYSTEM. We consider the engines using a combined lubrication system whereby the engine components that are loaded most heavily are lubricated by forced oil circulation, while other, less loaded parts, are lubricated by splash and by gravity.

Lubricated by forced oil circulation are the crankshaft main bearings and connecting rod big-end bearings, the valve mechanism, the camshaft bushings, and timing gear bushings. The engine lubrication system includes oil pan, oil pump, oil filter, oil cooler, oil ducts and lines, oil pressure gauge, and oil filler. The oil level in the crankcase is checked with dipstick when the engine stands still.

The forced oil circulation circuit in most automotive engines is the same. With the engine running, the crankcase oil is drawn by the gear-type oil pump which delivers it under pressure to the oil filter. The clean oil leaving the filter is cooled in the oil cooler, whence it passes into main oil gallery. From the main oil gallery the oil flows through ducts in the cylinder block to the crankshaft main bearings and the camshaft bearing journals.

Flowing through the angular oil passages drilled in the crankshaft, the oil enters crankpin oil cavities, where it is additionally cleaned, and emerges on the crankpin surfaces to lubricate the connecting rod bearings. From the first crankshaft main bearing the oil is ducted to the spindle of idler gear and the fuel pump drive gear bushing.

Through a cross-drilling in one of the camshaft bearing journals the oil is fed

Intermittently into hollow rocker-arm shaft by a duct extending upwards through the cylinder block and cylinder head and an external supply pipe. The oil is distributed to each rocker bearing bushing through radial drillings in the rocker- arm shaft. The oil escaping from the rocker bearing runs down the push- rods to lubricate the valve lifters and cams.

The cylinder walls, piston skirts and pins, and timing gears are lubricated by splash. With the crankshaft rotating rapidly, the oil escaping from the crankshaft bearings and that draining from the valve mechanism is flung off in fine droplets from the big end bearings to form an oil mist. The oil droplets setting onto the surfaces of the cylinders, pistons, and cams lubricate them and run down into the oil pan, whence the oil starts again on its circuit. The piston pin is lubricated with the oil droplets that get into the hole in the connecting rod small end. In engines having oil passages drilled through their connecting rods, the piston pins are lubricated by forced oil circulation.

The operation of the engine lubrication system is monitored by watching pressure gauge that reads the oil pressure in the main oil gallery. Some engines are additionally equipped with an oil temperature gauge and an oil pressure indicator light. The light is off when the oil pressure is normal. But if the pressure drops too low, the light comes on.

The system uses a duplex oil pump. From oil pump main section oil is delivered to twin oil filter, with its two sections operating in parallel. Some of the oil cleaned in the filter is drained, after being used to drive the filter rotors, to the oil pan. The rest of the cleaned oil is supplied under pressure into main oil gallery, whence it is ducted to the rubbing engine components. The valve mechanism is lubricated with the oil supplied through hollow bolt, pivoting cam follower, and hollow push -rod.

Oil pump cooler section delivers oil to cooler, whence the cooled oil drains into the oil pan. In winter time, the oil delivered by the cooler section of the oil pump can be made to flow direct into the oil pan, by-passing the oil cooler. This is done by turning the handle of two-way cock through 180°.

The engine crankcase is filled with oil through filler. It is recommended that after filling the crankcase with oil, the engine should be run for two or three minutes to fill the entire lubrication system. Then the engine should be stopped, and the oil should be allowed to drain (for 10 minutes) into the oil pan. After that, the oil level in the oil pan should be checked.

To check the level of the oil in the oil pan, use is made of dipstick. To use the dipstick, pull it out, wipe it off, and put it back in place. Then pull it out again so that you can check the level of the oil shown on the dipstick against the markings stamped in its lower part. With the engine standing still, the oil level should register with the upper marking on the dipstick. If the level stays below the lower marking on the dipstick when the engine is stopped, the engine must not be started until the crankcase is topped up. The excess oil, if any, is drained from the crankcase through the hole in the oil pan that is closed by plug.