Oil Pump: Inspection
Mating surface of the oil pump cover should be smooth. Replace pump assembly if cover is scratched or grooved.
Lay a straightedge across the pump cover surface (Fig 1). If a 0.038 mm (0.0015 inch) feeler gauge can be inserted between cover and straightedge, pump assembly should be replaced.
Measure thickness and diameter of OUTER rotor. If outer rotor thickness measures 20.9 mm (0.825 inch) or less or if the diameter is 62.7 mm (2.469 inches) or less, replace outer rotor (Fig 2).
If inner rotor measures 20.9 mm (0.825 inch) or less, replace inner rotor and shaft assembly (Fig 3).
Slide outer rotor into pump body. Press rotor to the side with your fingers and measure clearance between rotor and pump body (Fig 4). If clearance is 0.356 mm (0.014 inch) or more, replace oil pump assembly.
Install inner rotor and shaft into pump body. If clearance between inner and outer rotors is 0.203 mm (0.008 inch) or more, replace shaft and both rotors (Fig 5).
Place a straightedge across the face of the pump, between bolt holes. If a feeler gauge of 0.102 mm (0.004 inch) or more can be inserted between rotors and the straightedge, replace pump assembly (Fig 6).
Inspect oil pressure relief valve plunger for scoring and free operation in its bore. Small marks may be removed with 400-grit wet or dry sandpaper.
The relief valve spring has a free length of approximately 49.5 mm (1.95 inches). The spring should test between 19.5 and 20.5 pounds when compressed to 34 mm (1-11/32 inches). Replace spring that fails to meet these specifications (Fig 7).
If oil pressure was low and pump is within specifications, inspect for worn engine bearings or other reasons for oil pressure loss.