Olds Pump=More Oil pressure=Leaking Rear Main

Posted by Joe Hall On 2007/8/4 19:10:54

Of the other people running an Olds oil pump, has anyone found their rear main seal leaks after installation? That has been my experience thus far.

When I installed the Olds pump, I also installed a modern, neoprene rear main seal. This has proven to be an acceptable replacement for the rope seal, and I have confidence in it.

After I first put the engine back together, on a 30+ mile test drive I discovered the rear main seal was leaking (more like pouring). So I tore it back down and double checked installation of the seal, but could not find anything wrong. So I reassembled the engine, and now find it is still leaking.

This time I did the test "drive" with the car still up on ramps. Warmed up and at idle (45psi of oil pressure indicated), there is no leak; at 1300 rpm there is no leak. However, at sustained 2000rpm (65 psi indicated), it begins to leak in less than a minute, at a rate of about one drop every three to five seconds.

Looking at a spare engine, it appears the lube oil coming out the rear side of the main bearing returns to the sump via a slit in the bottom of the main cap. That slit, measured from out side is about 1 3/8" long X 1/4" wide. This measurement is deceptive though, since it is much smaller on the inside, plus the rear edge of the main bearing fills in some of the inner side of the slit.

My hypothesis at this point is at sustained higher rpm, the slit in the main cap cannot dump the lube oil being by the main bearing fast enough; the cavity fills up and builds pressure; itthen begins to push the oil past the seal.

My plan is to increase the size of the slit as much as possible with a dremmell and try it again. (But I am getting VERY tired of removing the oil pan.)

What say ye Olds pump wizards? :)

Joe H