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TR2/3/3A Oil Pump Wear

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J

Joel M

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I disassembled my original oil pump today to check the end float of the rotors. Not sure of the best procedure, but I used a feeler gauge and a straight edge to check the gap between rotor and pump body, as well as the recess on the cover plate caused by rotor wear. The rotor to pump body clearance was 3.5 mils, and the cover plate wear was about 1 mil. This give a total clearance of 4.5 mils compared to the maximum spec of 2.5 mils (the rotor heights were also about 1/2 mil under spec, so that's a contributor). Also, there is some slight scoring on the bottom of the rotors (see picture). I can easily take out the cover plate wear, but is there any concern taking down the pump body and rotors (to remove score marks) in order to get proper clearance? I know it might be suggested to buy new - and I will if necessary - but I'm trying to refurbish/refresh as many original parts as I can given the general lack of quality I've encountered in reproductions.

Oil_Pump.jpg
 
That pump definitely swallowed some metal.

If you wish to reset the tolerance, use 220grit wet or dry on either a granite or glass table top. Using circular motions, and a lot of sand paper changes, work the parts back to proper clearance. Sand the cover flat. Sand the rotor ends flat and equal to one another. Then, sand the case opening until the rotors have the proper clearance.

It takes a while, but gets the pump back to better than new.
 
The book talks about lapping the end plate and body together, which is what I've always done. Just smear a little valve grinding compound and start rubbing. Just watch that you don't get the end plate too far away from flat.

But first check the clearance between inner and outer rotor, plus outer rotor to housing. Those cannot be fixed by lapping. IIRC, the book calls for .010" max.

Also look carefully for cracks in the outer rotor, preferably while trying to spread it with your fingers.

One other thing, not normally an issue: look at the corners on the outer rotor. If one end has a chamfer or radius, it should be the one to go away from the end plate.
 
In the past I have purchased some very usable oil pumps on evil bay for like 20 bucks. IHO an oil pump usually has an easy life plus a lot of people purchase new and sell the old one. The old ones are usually dirty but clean up.
 
TR3driver said:
But first check the clearance between inner and outer rotor, plus outer rotor to housing. Those cannot be fixed by lapping. IIRC, the book calls for .010" max.
Click to expand...

10 mils is the spec out of the TR4 service manual. My pump measured 6 mils, so I should be good according to that. However, I'm a little confused by the TR3 service manual spec. It shows "clearance on rotors" of 0.0005 to 0.0025 minimum, and 0.001 to 0.004 maximum. I think that cannot be describing the same thing as clearance between rotors for the TR4 due to the large discrepancy, and not sure about the 2 tolerances for min and max. What could this be specifying?

TR3
Oil Pump TR3 Specs.jpg

TR4
Oil Pump TR4 Spec.jpg
 
Nevermind. I see now that it's just the rotor end clearance. I should be good now for rebuilding the unit! Thanks!
 
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