(Image/Jim Smart)

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.

We’re working with a simple Ford gerotor oil pump, also known as a positive displacement pump. Marvin has disassembled this Melling pump right out of the box and has found no significant issues. He checks clearances before doing any work, then, cleans up the cavity to ensure smooth flow. He also checks the relief valve. (Image/Jim Smart)
When you examine the cavity, there are rough cast surfaces that could use a cleaning up. Marvin grinds and hand-massages these surfaces to reduce turbulence. (Image/Jim Smart)
Endplay is checked along with rotor to housing clearances before any work is performed on the housing. Rotor endplay should be 0.0011 to 0.0041 inch. Rotor to housing clearance should be 0.006 to 0.012 inch. Relief valve clearance should be 0.0015 to 0.0029 inch. (Image/Jim Smart)
All sharp edges are cleaned up as shown with a grinder to reduce oil turbulence, then hand massaged with 180 to 400 grit sandpaper. This is time consuming, but worth the effort. (Image/Jim Smart)
Stress risers are cleaned up to prevent cracking. (Image/Jim Smart)
All transitional passages are massaged to look like this to reduce turbulence. (Image/Jim Smart)
Marvin does a gasket match-up to ensure the gasket doesn’t interfere with flow. (Image/Jim Smart)
A quick pass is performed with a ball hone to clean up the relief valve bore. (Image/Jim Smart)
Housing and cover plates are dressed on 400 grit sandpaper atop a piece of plate glass or a perfect steel surface to remove any irregularities. As you work these parts, examine surfaces for high and low spots. (Image/Jim Smart)
As you can see, Marvin has cleaned up rough surfaces to smooth flow. This is time intensive with a lot of hand work to smooth the cavity. Be prepared to sit on a sofa watching your favorite sitcom while doing this. (Image/Jim Smart)
This is the relief valve piston, which is inspected for ragged edges and high spots that can cause sticking. (Image/Jim Smart)
The relief valve bore gets a shot of engine assembly lube, then, the piston checked for smooth function. It must float smoothly through the bore and fall out in your hand. (Image/Jim Smart)
The relief valve piston is installed like this and again checked for smooth function. Never install it dry. (Image/Jim Smart)
The relief valve expansion cup is installed like this with the wall pointed toward the spring and piston. The spring will fit within the cup. (Image/Jim Smart)
The cup is driven into the pump as shown with a deep well socket. (Image/Jim Smart)
Inner and outer rotor surfaces are checked for irregularities (high and low spots). Any visible flaws are cause for rejection. (Image/Jim Smart)
Contact surfaces are lubricated with engine assembly lube for a good lubrication barrier on start-up. Marvin has applied Pioneer dry graphite lubricant, which is for use on engine or mechanical parts prior to assembly. Once assembled, the cavity is filled with Comp Cams Engine Assembly Lube. (Image/Jim Smart)
Once assembled, the pump is checked for freedom of rotation and any interference. Rotation should be as smooth as butter. (Image/Jim Smart)
Oil pump cover plate ARP bolts are torqued to 6 to 9 lbs-ft. (Image/Jim Smart)
All of Marvin’s builds included safety wire to ensure security. This doesn’t mean you have to do it. A good thread locker will secure the bolts. (Image/Jim Smart)
Any engine build, including dead stock, must be fitted with an ARP oil pump driveshaft. Stock shafts, especially Ford, should be tossed in favor of the ARP shaft. (Image/Jim Smart)
Because lubrication involves more than just the pump, we’re going to take you through the engine. Lifter bores should be checked for proper side clearances. Bores should get a quick pass with a hone for a good crosshatch pattern and oil control. (Image/Jim Smart)
These lifter bores have been cleaned up with a hone. Red GE Glyptal coating has been applied to seal the casting and improve return flow back to the pan. (Image/Jim Smart)
Marvin always stressed massaging oil galley passages to reduce turbulence as shown. This should be a part of your engine blueprinting routine during the build when the block is bare and can be cleaned up. (Image/Jim Smart)
All oil galley passages should be checked with a bright inspection light and their edges cleaned up. (Image/Jim Smart)
Oil drainback passages get these screens to keep any dangerous debris out of the oil pan. (Image/Jim Smart)
Good oil pressure (10 pounds for every 1,000 rpm) isn’t just about pump health, but proper bearing clearances at the mains, rods, and cam bearings. Low oil pressure with a good pump indicates excessive bearing clearances. (Image/Jim Smart)
Chamfering oil holes in the crank journals improves oil flow across the bearings and journals. (Image/Jim Smart)
Where the factory has installed press-in oil galley plugs, screw-in oil galley plugs are a must to prevent failure and a loss of oil pressure. Marvin always drilled a 0.032 inch hole in the top plug to improve oil flow at the timing set. (Image/Jim Smart)
I did quite a number of engine builds with this man—Marvin McAfee of MCE Engines (Marvin’s Custom Engines) in Los Angeles, California. We built engines together for approaching 20 years. Marvin passed a couple of years ago from natural causes. He was 87 and is surely missed. (Image/Jim Smart)

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Author: Jim Smart