The pin closes the oil galley from the front oil port (pump output) to the rear port (the remaining lube system). With the pin out the oil galley is open from the front to the back port.

When the pin is driven in the oil galley is now closed and oil MUST be routed from the front port to the back port in order for oil to get from the pump to the rest of the engine. Putting the filter in the line connecting these ports will filter all the oil pumped.

Remember 9-11-01--God Bless the USA
JUSTICE, not REVENGE, will prevail

1951 Chevy 1/2-ton Pickup truck