Replacement Harley oil pumps must be primed after installation but before their first use in order to prevent “air lock” or cavitation. Essentially, air trapped inside the pump while it was out of the crankcase prevents oil from flowing and the engine quickly goes dry. It is a mistake one rarely makes twice since the engine may practically explode within a few hundred yards of leaving the garage on the first test ride. Oil pump manufacturers including S&S, Harley-Davidson and Sifton drily note that substantial engine damage not covered under warranty may result from failing to prime an oil pump.
Install the oil pump. Connect feeder and return lines. Fill the oil tank to correct level.
Remove check valve cover screw with a flat head screwdriver. Remove the check valve O-ring and spring by hand.
Remove the check valve ball with a mechanic’s magnet from inside the oil pump body. On a typical Harley oil pump the check valve cover screw is on top of the oil pump body.
Look inside the open check valve. The exposed cavity inside the oil pump should fill with oil within seconds.
Pour clean engine oil into the cavity if it remains empty and wait for five minutes.
Replace the check valve ball, spring, O-ring and screw. Put the motorcycle in "Neutral" and start the engine.
Confirm oil circulation with an oil pressure gauge and by removing the filler cap from the oil tank and watching oil return to the tank.