There is a bypass valve in the oil pump. This bypass valve controls the pressure of the oil coming from the oil pump. The oil pump can put more oil into the system than is needed. When there is more oil than needed, the oil pressure goes up and the bypass valve opens. This lets the oil that is not needed go back to the oil pan.
The output of the oil pump goes to the oil manifold in the cylinder block. The oil manifold is the source for oil under pressure for the engine and its attachments. Connecting drilled passages from the oil manifold are the way for the oil to get to the main bearings, timing gear bearings, and the bearings for the rocker arm shaft.
The flow of oil which goes to the main bearings is divided. Some of the oil is the lubricant between the main bearings and the bearing surfaces (journals) of the crankshaft. Some of the oil goes through passages drilled in the crankshaft. This oil is the lubricant between the connecting rod bearings and the bearing surfaces (journals) of the crankshaft. The rest of the oil goes out through orifices in the block near the main bearings. This oil is both a coolant and a lubricant for the pistons, piston pins, cylinder walls and the piston rings.
Oil also goes through connecting passages in the cylinder block and cylinder head. This oil is the lubricant for the rocker arm shaft and bearings and for the rocker arms. Some of the oil is the lubricant for the valve stems. The rest of the oil drains on the cylinder head where it is the lubricant for the push rods and valve lifters and the cams for the camshaft.
On the 3306 Engines, this oil is the lubricant for the intermediate and rear camshaft bearings.
On the 3304 Engines, the bearings for the camshaft get lubrication oil under pressure through passages drilled in the cylinder block to the oil manifold.
The oil supply passage for the rocker arms is in a different location in the engine w/ spacer plate. Engines w/o a spacer plate have an oil passage from the rear of the cylinder block to a head bolt hole in the block. The oil flows around the head bolt, up through the cylinder head and rocker arm shaft bracket, to the rocker arm shaft.
ROCKER ARM OIL SUPPLY (Engines without spacerplate)
ROCKER ARM OIL SUPPLY (Engine w/ spacer plate)
Engines w/ spacer plate have an oil passage from the rear of the cylinder block that goes below the head bolt hole and connects with a drilled passage that goes up next to the head bolt hole. A hollow dowel connects the vertical oil passage in the cylinder block to the oil passage in the head. The spacer plate has a hole with a counterbore on each side that the hollow dowel goes through. An O-ring is in each counterbore to prevent oil leakage around the hollow dowel. Oil flows through the hollow dowel into a vertical passage in the cylinder head to the rocker arm shaft bracket. The rocker arm shaft has an orifice to restrict the oil flow to the rocker arms. The rear rocker arm bracket also has an O-ring that seals against the head bolt. This seal prevents oil from going down around the head bolt and leaking past the head gasket or spacer plate gasket. The O-ring must be replaced each time the head bolt is removed from the rear rocker arm bracket.
All the timing gear bearings get lubricant under pressure from the oil manifold through connecting drilled passages.
Oil goes to the components and attachments on the outside of the engine through supply lines which connect to the oil manifold. These components and attachments are: turbocharger, air compressor, Woodward governor and others.
After the lubrication oil has done its work, it goes back to the engine oil pan.