supplies a thin film of oil that prevents metal-to-metal
easily in the piston ring grooves and on the cylinder
contact, thus greatly reducing friction. The crankshaft,
connecting rods, bearings, pistons, piston rings, valve
As oil circulates through the engine, it tends to
stems, valve tappets, gears, drives, couplings, and
wash off and carry away dirt, particles of carbon, and
bearings are the main parts that must be lubricated to
other foreign matter into the crankcase, where the
larger particles drop to the bottom of the pan. The oil
filter removes many of the smaller particles.
Helping to cool the engine is another function of
the lubrication system. The oil goes through some very
LUBRICATION SYSTEM COMPONENTS
hot regions in the engine, and heat is absorbed by the
oil, thus raising the oil temperature. The heat so
All modern engines are lubricated under pressure.
absorbed is carried back to the oil pan, from which it is
The oil supply is carried in the oil pan attached to the
dissipated into the surrounding air.
underside of the crankcase, from which it is drawn up
and forced through a network of tubes, pipes, and
Other purposes of lubricating oil are absorbing
drilled passages by the oil pump. The other main
shocks between bearings and other engine parts,
components of the system are the oil pressure gauge,
forming a seal between piston rings and cylinder walls,
the oil strainer, the oil filter, the oil level gauge, and the
and helping to clean the engine parts.
oil temperature regulator (oil cooler).
As a shock-absorbing agent, oil around the piston
NOTE: Not all engines are equipped with oil
bearings and journals acts as a cushion against the jars
they receive from the hammer-like blows of the thrusts
of the piston. A load of as much as one and a quarter
tons is suddenly thrown upon the top of the piston
when combustion takes place. This sudden thrust on
The oil pump is the heart of the engine lubricating
the piston is carried through the piston pin and
system. Depending on the type of engine, the pump
connecting rod bearings. Oil helps quiet the piston
will be mounted either inside or outside the crankcase.
movement and reduces the wear of its parts.
The two common types of oil pumps generally used in
automotive engines are the gear and the rotary.
Piston rings must form a gastight seal with the
cylinder walls. The lubricating oil delivered to the
GEAR PUMP.--The gear pump (fig. 5-12)
cylinder walls helps in this respect. The oil film also
consists of two pump gears mounted within a close
fitting housing. One of these two pump gears is driven
provides lubrication of the rings so they can move
VA LV E
Figure 5-12.--Gear oil pump.