Oil Pump Basics
Your oil pump is an extremely important part of your engine. It is solely responsible for pumping your engines life blood (oil) through your engine. An oil pump is not an area to try and save a few bucks.
The pump is driven by a slot in the end of the cam so it turns 1/2 as fast as the crankshaft which is more than enough to pump pressures up over 200+ psi when the engine is cold. Before you install a pump on your engine, you need to ensure it's not worn to a point where you will have low oil pressure.
1 - , 2 - , 3 -
Photo 1 shows how you check the pump gears for excessive wear. This pump was almost new and had only .002" between the top of the pump case and the top of the pump gears. If you have more than 004", I would consider finding a new pump because you will likely have low oil pressure. Photo 2 shows a basic steel full-flow pump cover (this one is made by Gene Berg). I would not recommend using an aluminum pump cover due to accelerated wear of the aluminum by the steel pump gears since they are constantly rubbing. Photo 3 shows wear marks on the back of the pump cover. Since this one was a high quality steel unit, no wear could be felt (only seen by the light rub marks). If yours has swirls that can be felt, replace it!!
Another place to check, with a pair of calipers this time, is outer diameter of the front of your pump and compare that measurement to the inside diameter of your engine case where it fits in. The outer diameter of your pump housing should be slightly larger by a thousandth or so than the case bore to provide an "interference fit" when assembled and torqued. If it's smaller, you will have some of your oil pressure on the high pressure side of the pump lost in the small gap between the two surfaces. Lost oil pressure is NOT good for your engine.
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Revised: August 29, 2003 .