Oil Pump RestorationRebuilding is better than replacing
Most high-production engine rebuilders simply replace the oil pump when rebuilding an engine. Reason? Oil pumps are relatively inexpensive, and for most popular engines, high-pressure and high-volume pumps are readily available. But for those rebuilding a less popular "fringe" engine, you will have to restore-or more accurately "blueprint"-the existing pump. Although it sounds technical, the actual process is relatively easy and requires only a set of feeler gauges, a flat surface and some sandpaper. Best of all, it should only cost you a couple of bucks for materials.
Most oil pumps are gear pumps or gearotor pumps. They suck oil up out of the oil pan and pressurize the oil passages in the engine. Both types are positive-displacement pumps and would produce too much pressure if not for an oil-relief valve that bypasses oil back to the suction side of the pump if pressure builds above a preset relief pressure. However, there may be times when engine demand exceeds pump capacity, especially at high rpm if the pump is not in top-notch operating condition. Typically, what happens is the gear or gearotor end clearance becomes excessive from wear or sloppy assembly tolerances and oil leaks by the edge of the gears instead of pressurizing the engine. Oil-pump blueprinting or restoration involves bringing the pump gear end clearances back into specification. These clearances are restored by sanding the oil pump body and cover on a flat surface such as a surface plate (shown) or a piece of flat glass on, in some cases, the ends of the pump gears.
The other part of oil-pump blueprinting is to install a new pressure-relief spring of the correct pressure for your engine. Shown is a new stronger spring alongside the original relief spring for this Buick 455 oil pump. Consult specialty shops that deal in your make and model of engine for these small components. They usually have the proper spring for your specific engine. Most oil pumps use steel castings for housings, but some such as this Buick external oil pump (located outside of the oil pan) are made of aluminum. It's critical to inspect the oil pump housing for excessive wear, grooving and galling of the gear cavity. This damage is sometimes a result of too many miles, but more likely it's been caused by dirt in the oil system. If the wear isn't too deep on the gear end surfaces, the pump can be successfully restored. If the pump housing is scored or grooved on the edge surfaces of the gears (sides of the housing), you need another pump core to rebuild.
The most important clearance you are trying to establish is the gear end clearance. It can be checked by turning the oil pump housing upside down inserting the gears in the housing on their shafts and placing a straightedge across the gasket surface of the pump housing. Then slide a feeler gauge between the gear and the straightedge to determine the clearance. If it is too much, you must sand the pump-housing gasket surface on a flat plate. If the clearance is too tight (very rare), you can sand the ends of the gears on a flat surface. Consult the shop manual for your engine to find out what the minimum gear end clearance is and shoot for that figure. It will greatly increase the efficiency of your oil pump. After you have established the correct gear end clearance, you need to sand the pump cover on a flat surface to remove any wear grooves and to make certain that it is perfectly flat.
After the proper clearances have been established, all of the oil pump components should be meticulously cleaned and blown dry with compressed air. The pump can be reassembled with the new pressure-relief spring using engine oil to lubricate the pressure-relief valve in its bore. Then the gears can be installed on their shafts. Most gears have some identification mark such as a punch mark that should point to the cover. The real trick is to fully pack the gears and pump cavity with petroleum jelly, normally used for medical purposes. DO NOT USE ANY TYPE OF AUTOMOTIVE GREASE! The petroleum jelly will help prime the pump, and the engine oil will displace the petroleum jelly easily. Engine oil will not displace wheel-bearing or white grease, and the result will be no oil pressure. Always check a rebuilt engine for oil pressure by turning it over with the starter with the spark plugs removed. If you took your time blueprinting the oil pump, you should be rewarded with excellent oil pressure and a few extra bucks saved on the engine rebuild.
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