TROUBLESHOOTING THE HMMWV - OD1616 - LESSON 1/TASK 1
that develops between moving parts as a result of friction.
In
addition, the oil that is supplied to the cylinder walls helps the
piston rings make a good seal to reduce blowby.
(a) Oil as a lubricant. The primary function of engine oil is
to reduce friction between moving parts (lubricate).
Friction, in
addition to wasting engine power, creates destructive heat and can
cause rapid wear of engine parts.
The greater the friction, the
greater the energy needed to overcome that friction. The increase in
energy adds to the amount of heat generated, causing moving parts
that are deprived of oil to melt, fuse, and seize after a very short
period of engine operation.
The effectiveness of a modern
lubrication system makes possible the use of friction-type bearings
in an engine. Friction between the pistons and the cylinder walls is
severe, making effective lubrication of this area imperative.
Lubrication of the connecting rod and main bearings is crucial
because of the heavy loads that are placed on them. There are many
other less critical engine parts that also need a constant supply of
oil, such as the camshaft, valve stems, rocker arms, and timing
chains.
(b) Oil as a Coolant.
Engine oil circulated throughout the
engine also serves to remove heat from the friction points. The oil
circulates through the engine and drains to the sump.
The heat
picked up by the oil while it is circulated is removed by an airflow
around the outside of the sump. In some instances, where the sump is
not exposed to a flow of air, it is necessary to add an oil cooling
unit that transfers the heat from the oil to the engine cooling
system through an oil cooler mounted in front of the radiator.
The
HMMWV has this type of cooler.
(2) Characteristics and Operation of the HMMWV's Lubrication
System.
The lubricating system in the HMMWV engine is a pressure
feed type. Normal operating pressure for the system is 20 to 50 psi;
while at idle, the operating pressure may drop down to 15 psi. The
engine crankcase (minus the oil filter) contains seven quarts, and
eight quarts with the filter.
There are three different weights of oil that are used in the HMMWV
engine, depending on the temperature range in which the vehicle is
expected
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