Although the oil pump is probably the best-lubricated part of the engine, it is lubricated before the oil passes through the filter. Therefore, it can experience premature failure because of dirt or other materials entering the pump. Foreign particles can cause three kinds of trouble in a pump:
- Fine abrasive particles gradually wear the surfaces, causing a reduction in efficiency.
- Hard particles larger than the clearances can cause scoring and raising of metal as they pass through, finally resulting in seizure.
- Large particles that cannot pass through will physically lock up the pump.
Of course, when the pump seizes or locks up, the intermediate or drive shaft will also be twisted or sheared off.
To thoroughly inspect the oil pump, it must be disassembled.
- After the pump has been disassembled and cleaned, inspect the pump gears or rotors for chipping, galling, pitting, or signs of abnormal wear.
- Examine the housing bores for similar signs of wear.
- If any part of the housing is scored or noticeably worn, replace the pump as an entire assembly.
- Check the mating surface of the pump cover for wear.
- If it is worn, scored, or grooved, replace the pump.
- Use a feeler gauge and straightedge to check the flatness of the cover. The service manual gives the maximum and minimum acceptable feeler gauge thicknesses for the cover.
- If the cover is excessively worn, grooved, or scratched, it should be replaced.
- Use an outside micrometer to measure the diameter and thickness of the outer rotor. The inner rotor's thickness should also be checked. If these dimensions are less than the specified amount, the rotors must be replaced.
Measuring the outer rotor with an outside micrometer.