The oil pumps primary purpose is to circulate engine oil under pressure to the bearings, pistons and the camshaft. This lubricates these systems, allows the use of higher-capacity fluid bearings and also assists in engine cooling.
The valve which allows mixture into the cylinder is the inlet valve; the one through which the spent gases escape is the exhaust valve. They are designed to open and close at precise moments, to allow the engine to run efficiently at all speeds.
For Isuzu FVZ & FVR model trucks with the 6HK1 engine.