In this post I will be inspecting and measuring the oil pump off my 1995 core engine. This engine came out of a wrecked truck with roughly 161K miles on the odometer. The oil pump tolerance specifications are at the end of this post for future reference.
Above is the the timing cover portion of the oil pump. This is an aluminum casting that is machined. Note the machining marks as well as the scoring around the outer diameter of the oil pump cavity.
Here is a closer look at the timing cover. This particular unit shows wear from either lack of lubrication or hard debris running through it. You can see and feel the grooves worn into the aluminum. These surfaces should be smooth.
The cover plate that retains the oil pump in the cover also showed signs of wear similar to the aluminum housing.
The outer rotor of the oil pump showed heavy wear on both sides and the outer diameter. Also note the dark marks on the surface of the inner lobes.
Here is a close up of the outer rotor lobes . The dark spots are indentations from hard debris running through the pump.
The inner rotor showed the same wear as the outer rotor on both sides.
Here is a close up the the debris damage on the inner rotor. This matches what was found on the outer rotor.
Above shows the tip to tip clearance between the rotors on this pump. 0.004" is within the spec of 0.023"
Clearance between the outer rotor and the housing measured 0.004". This is still within the 0.006" maximum clearance spec.
Clearance over the rotors measured at 0.0025". This is still within the maximum clearance spec of 0.0075".
Thickness of the outer rotor measured at 0.588" and is above the minimum spec of 0.5876".
The diameter of the outer rotor measured at 3.246" which just meets the minimum diameter spec.
The inner rotor thickness at 0.588" is still above the minimum spec of 0.5876".
This pump shows damage from debris but still measures within spec and will continue to function. It would be recommended to replace the rotors for extended service. Looking at the design of the pump a reputable machinist would be able to repair the aluminum timing cover. The cover would need machined down in a few areas and a bushing pressed in to bring a heavily worn cover back into spec. This is worth pursuing as replacement timing covers are no longer available and many used ones are in similar condition to the cover in this article.
Clearance over Rotors (Max) - 0.0075" (0.1906 mm)
Cover out of Flat (Max) - 0.002" (0.051 mm)
Inner Rotor Thickness (Min) - 0.5876"-0.5886" (14.925-14.950 mm)
Outer Rotor Thickness (Min) - 0.5876" (14.925 mm)
Outer Rotor Diameter (Min) - 3.246" (82.461 mm)
Outer Rotor Clearance (Max) - 0.006" (0.1626 mm)
Tip Clearance between Rotors (Max) - 0.023" (0.584 mm)