ARMY TM 92815-252-24
AIR FORCE TO 38G1-92-2
Section I. PRINCIPLES OF OPERATION
This section contains functional descriptions of the engine systems and how they are connected to the end item.
2-2. COOLING SYSTEM.
The cooling system consists of a radiator, hoses, thermostat, belt driven fan, water pump, and cooling jackets within the
engine. The water pump forces coolant through passages (coolant jackets) in the engine block and cylinder head where
coolant absorbs heat from the engine. When the coolant temperature is below operating temperature, the thermostat is
closed and coolant is bypassed to the water pump inlet. As coolant temperature increases to 160°F (71 C), the
thermostat starts to open, restricting bypass flow and opening flow to the radiator. As coolant temperature continues to
increase to 1850F (85°C), the thermostat is fully opened, shutting off all bypass flow and providing full flow through the
radiator. Air forced through the fins of the radiator by the fan cools the coolant pumped through the radiator. Items are
added to the engine to monitor coolant temperature and to warn if temperature exceeds a predetermined value.
2-3. LUBRICATION SYSTEM.
The lubrication system consists of an oil sump, dipstick, pump, relief valve, and filter. The oil sump is a reservoir for
lubricating oil. The dipstick indicates oil level in sump. The pump draws oil from the sump through a screen which
removes large impurities. The oil then passes through a relief valve preset to limit oil pressure to 47 to 59 psi (324 to
407 kPa). The oil then passes through a spin-on type filter where small impurities are removed. From the filter, oil
enters the cylinder head oil gallery and flows to the crankshaft and bearings. The connecting rod bearings are pressure
fed through internal drillings in the crankshaft from the supply to the main bearings. Splash oil lubricates the gears, and
the underside of the pistons. The governor camshaft is lubricated by a drilled bolt/oil jet. An internal crankcase drilling
provides an oil feed to the hydraulic tappets. After passing through the block, the oil returns to the oil sump. Items are
added to monitor oil pressure and to warn/stop engine if pressure drops to a dangerously low value.
2-4. FUEL SYSTEM.
2-4.1. The fuel system consists of an external fuel tank, electrically driven transfer pump, fuel filter/water separator, fuel
filter, fuel injection pump and fuel injector for each cylinder, and piping. Fuel from an external source is supplied to the
fuel injection pumps. The injection pumps provide a pressurized metered quantity of clean atomized fuel through the
injector nozzles into the cylinders at a precise time near the end of the compression stroke of each piston. The fuel that
is not used by the injectors is returned to the fuel tank via an excess fuel return line.
2-4.2. Extremely cold outside temperatures make starting the engine difficult. To improve engine starting, a cold
weather starting aid has been provided that features two heater plugs in the intake manifold. The heater plugs are
energized during engine preheat starting cycle.
2-5. ELECTRICAL SYSTEM.
The electrical system consists of external mounted batteries, starter, battery charging alternator, and related relays and
switches for control of the system. Battery power supplied to the starter during the start cycle energizes the starter which
engages the ring gear of the flywheel causing the engine to turn over. When engine start is complete, the starter is
deenergized and disengages from the flywheel.