Call it blind faith, but a lot of us have been installing new oil pumps right out of the box without giving them a detailed inspection. Most of the time, pumps are installed right out of the box without consequence. They have a good track record of reliable performance.
However, the most seasoned engine builders will tell you there are no unimportant parts. All parts warrant close inspection and massaging before installation.
This time, we’re going to pick on oil pumps.
Understanding an Engine’s Oiling System
I’ve had the good fortune of knowing and working with the late Marvin McAfee of MCE Engines in Los Angeles, California. We lost Marvin to natural causes at age 87. He was a terrific engine craftsman and educator and did it for a long time. With every engine build I’ve done with Marvin, I’ve absorbed vast amounts of engine building knowledge.
One has been the inspection and massaging of critical engine parts.
Marvin looked at important details a lot of engine builders tend to overlook. One of them has been the oil pump and engine lubrication system. An engine’s oiling system can be compared to the human cardiovascular system. We focus on the heart, yet there’s an entire plumbing system involved that gets blood to all parts of the body. The same can be said for an engine’s oiling system. The oil pump, like the heart, moves oil throughout the engine to keep things slippery. Oil galleys channel oil under pressure to all the engine’s moving parts, then, oil returns to the pan underneath.
Engine oil under pressure doesn’t just lubricate—it cools. We tend to believe coolant circulating through the radiator and water jackets does all the work of cooling. However, engine oil has intimate contact with the hottest parts in the engine, like exhaust valve stems and all of the bearings, providing a critical cushion between metal parts and carrying heat away.
Marvin looked at lubrication and cooling well beyond the oil pump.
He closely examined all the oil galleys and made it his business to remove rough surfaces that would cause oil turbulence plus the installation of screw-in oil galley plugs to keep things secure. He also inspected pump rotor/gear clearances to make sure they were within specs and that everything operated smoothly. Marvin commented oil pressure relief valves could stick causing overpressure or underpressure conditions and the risk of engine damage though such would be a rare occurrence.
What’s a Gerotor Oil Pump?
We’re working with a Ford positive displacement “gerotor” oil pump here. However, the same rules apply to gear pumps. Tolerances and relief valve function must be checked along with irregularities in the passages.
The “gerotor” name comes from the term “generated rotor.” It consists of an inner and outer rotor. The two rotors rotate on different axes. During the two rotor’s rotational cycle, volumes change continuously while moving oil through the cavity. An increase in flow gives us a vacuum. This vacuum creates a suction at the intake drawing oil into the cavity. The interaction between the two rotors moves oil through the cavity.
Oil isn’t compressed (because you cannot compress a liquid), but instead moved through the pump under pressure. The relief valve relieves any excess pressure.
Jim Smart is a veteran automotive journalist, technical editor, and historian with hundreds of how-to and feature articles to his credit. Jim's also an enthusiast, and has owned and restored many classic vehicles, including an impressive mix of vintage Ford Mustangs.