Oil Pump


Carefully remove the pressure relief valve and note the direction in which it is pointing so it can be reinstalled in its proper position. If the relief valve is installed backwards, the pump will not be able to build up pressure.

Before disassembling the pump, mark the gear teeth so they can be reassembled with the same tooth indexing.

Mark the gear teeth so they can be reassembled with the same indexing.

Some pumps have the gears or rotors marked when they are manufactured. Once all the serviceable parts have been removed, clean them and dry them off with compressed air.

Use a paint stick or other non-violent means to mark the gears, if possible. If a center punch is used, make sure you file down the raised material around the indent before reassembling the pump. The raised material that results from making the indent may cause interference and wear if not removed.

After the pump has been disassembled and cleaned, inspect the pump.

With rotor pumps, assemble the rotors back into the pump body. Use a feeler gauge to check the clearance between the outer rotor and pump body.

Checking clearance between the outer rotor and pump body.

If the manufacturer's specifications are not available, replace the pump or rotors if the measured clearance is greater than 0.012 inch (0.3048 mm).

After checking the outer rotor-to-pump housing clearance, position the inner and outer rotor lobes so they face each other. Measure the clearance between them with a feeler gauge. A clearance of more than 0.010 inch (0.2540 mm) is unacceptable.

Measuring the distance between the inner and outer rotor lobes.

On a gear-type pump, it is important to measure the clearance between the gear teeth and pump housing. Take several measurements at various locations around the housing and compare the readings. If the clearance at any point exceeds 0.005 inch (0.0762 mm), replace the pump as an assembly.

Taking several measurements around the housing. Courtesy of General Motors Corporation - Chevrolet Motor Division.

On both gear or rotor oil pumps, place a straightedge across the pump housing and measure the clearance between the straightedge and gears.

Measuring clearance between a straight-edge and gears. Courtesy of General Motors Corporation - Chevrolet Motor Division.

To ensure an accurate reading, make sure the housing surface is clean and free of residual gasket material and that the gears are bottomed in the bore. The desired end play clearance should not exceed 0.003 inch (0.1270 mm).

If the pump uses a hexagonal drive shaft, inspect the pump drive and shaft to make sure the corners are not rounded. Check the drive shaft-to-housing bearing clearance by measuring the outer diameter of the shaft and the inner diameter of the housing bearing.

The gasket used to seal the end housing is also designed to provide the proper clearance between the gears and end plate. Consequently, do not substitute another gasket or make a gasket to replace the original one. If a precut gasket was not originally used, seal the end housing with a thin bead of anaerobic sealing material.

Inspect the relief valve spring for signs of collapsing or wear. Check the relief valve spring tension according to specifications. Also, check the relief valve piston for scores and free operation in its bore.

The pickup screen and pump drive should be replaced when an engine is rebuilt.

Installation of oil pump and its intermediate shaft. Courtesy of Ford Motor Company.

The screen and drive must be properly positioned. This is important to avoid oil pan interference and to ensure that the pickup is always submerged in oil. To make the oil pump pickup tube installation easier, there are several types of drivers available that are suitable for use with air-powered equipment or with a light mallet.

Using a special driver and hammer to install the pickup tube into and oil pump. Courtesy of Goodson Shop Supplies.

Make sure the oil pump pickup tube is properly installed and be sure to use new gaskets and seals.

Use new gaskets and seals when installing the oil pump pickup tube.

Air leaks on the suction side of the oil pump can cause the pressure relief valve to hammer back and forth. Over a period of time, this will cause the valve to fail. Air leaks can also cause oil aeration, foaming, marginal lubrication, and premature engine wear. Care should be taken to make sure all parts on the suction side of the pump fit tightly and there is no place for air leakage. Air leakage often comes from cracked seams in the pickup tube.

On integral pumps, the timing case and gear thrust plate might be worn also. Wear here will limit pump efficiency due to excess clearance. Replace them as necessary.

The pump should be primed before assembly. This can be done by submerging it in oil or by packing it with lightweight assembly lube, petroleum jelly, or oil. Rotate the pump shaft to distribute the oil within the pump body.