RECOVERY VEHICLE, FULL TRACKED: MEDIUM, M88A1
LUBRICATION SYSTEM THEORY OF OPERATION
The main pressure oil pump draws oil from the pressure oil pump compartment in the oil pan. This compartment is fed by the
scavenge oil pump which picks up oil from the front end of the oil pan and by oil which drains into the pressure compartment
from the cover of the pressure pump compartment and the reserve compartment. The pressurized oil is forced through the engine
oil coolers and oil filter to the engine oil galleries, bearings, turbosuperchargers, fuel injection pump, and piston oil sprayer
nozzles. These nozzles are located in the crankcase below each cylinder and provide a continuous oil spray to the pistons and
cylinder walls. A pressure regulator valve, located on the right side of the crankshaft damper and oil filter housing, is influenced
by the pressure in the main bearing oil gallery and returns the incoming, excess, unfiltered oil to the oil pan.
The oil pan is a one-piece, aluminum-alloy casting divided into a pressure oil pump compartment, oil reserve compartment, and
sump compartment (at the front of the pan). Cored passages from each of the compartments terminate at a central outlet and
permit draining of all of the compartments from a single drainage point. A cored passage also permits draining the oil coolers
and oil filter compartment directly without permitting any sludge to enter the oil pan. The oil pan is designed to maintain a
constant oil level above the main pressure oil pump pickup tube in the pressure oil pump compartment during vehicle operation,
regardless of the angle at which the engine may be inclined.
The oil pump assembly consists of four sections combined as a single unit. The twin scavenge oil pump section of the unit
picks up oil from the front end compartment of the oil pan and delivers it to the main pressure oil pump compartment. The main
pressure oil pump section picks up oil from its respective compartment and supplies oil to the engine oil galleries and bearings,
and to the piston oil sprayer nozzles. The level in the pressure pump compartment is maintained by a dual-inlet leveling pump
which returns any excess oil to the reserve compartment. Oil is pumped from the reserve compartment by two makeup pumps
in a single section. These pumps pick up oil from opposite corners of the reserve compartment and discharge it into the pressure
pump compartment. The dual pump design ensures return of oil from the reserve compartment under all operating conditions
(cold oil, slope operation, etc.).
Oil Filters and Control Valves
The engine oil filters and the bypass valve are located in the crankshaft damper and oil filter housing at the front of the engine.
All engine oil passes through the oil filters. The oil filter bypass valve opens at the differential pressure of 35.6 psi (245 kPa).
The bypass valve permits oil to bypass the filters in the event that they become clogged.
Crankcase Breather System
The engine crankcase breather system is completely enclosed, which allows the engine to be submerged without the entrance of
water and permits the crankcase to be vented. The breather system is vented through the left turbocharger exhaust outlet into the
Engine and Transmission Oil Coolers
All transmission and engine oil cooling is accomplished by external oil coolers. The oil coolers are located on the sides of the
engine, above the cylinders. Air is drawn through the oil coolers by the cooling fans. A thermostatic bypass valve in each oil
cooler controls the temperature of the oil from the cooler by permitting cold oil to bypass the coolers. This valve also permits oil
to bypass the cooler in the event the cooler becomes clogged.
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