TM 9--2815--247--34 0004 00--6 THEORY OF OPERATION -- CONTINUED 0004 00 LUBRICATION SYSTEM -- CONTINUED General -- Continued 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. Oil Pan  The oil pan (Figure 1--1) is a one--piece aluminum alloy casting divided into a pressure oil pump compart- ment, oil reserve compartment, and the sump compartment at the front of the pan. Cored passages from each of the compartments terminate at a central outlet and permits draining all of the compartments from a single drainage point. A cored passage 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. Oil Pump  The oil pump assembly consists of four sections combined as a single unit. The 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, 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 make up pumps in a single pump 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 (Figure 1--8) and the bypass valve are located in the crank- shaft 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 a differential pressure of 35.6 psi (245.5 kpa). The bypass valve permits oil to bypass the filters in the event that they become clogged. Oil Sampling Drain Cock  An oil sampling drain cock (Figure 1--2) is located on the oil filter cover. The drain cock permits sampling of the engine oil to determine if its condition warrants an oil change. FUEL SYSTEM Fuel Supply Pump Assembly The engine--driven vane--type fuel supply pump assembly (Figure 1--1) is used to supply fuel under pressure to the fuel metering pump. The fuel pump is camshaft driven. Fuel Metering Pump  The fuel metering pump is located in the “V” of the engine between the fan drive housings, and supplies fuel under high pressure to each cylinder. The pump is driven at engine speed from the fan drive housing located at the rear of the engine. A fuel pump advance assembly is incorporated in the accessory drive housing to automatically provide a gradual degree advance of timing during the engine speed range from idle to 2600 rpm. Fuel Injector Nozzles and Tubes  Twelve fuel injector nozzles (Figure 1--9), one per cylinder, are used to inject fuel into the combustion chambers. Twelve fuel injector tubes of equal length carry the fuel from the fuel metering pump to the nozzles. The nozzles on each cylinder bank are interconnected by fuel return hoses to provide a path for the return excess fuel.