Rear main seal leak

[DRCBOWTIE]

Maybe someone here can make a suggestion. 72 Z28, original engine, engine was supposed to have been rebuilt about 8 years ago, not much mileage since.

So, rear main seal did not leak when my buddy recently purchased the car. Someone put in a non stock cam so he decided to do the right cam, and had local engine builder do a basic rebuild also; bearings, rings, etc. Result, the rear main started leaking.

This is a trusted local engine builder, and he was surprised to see it leaking. Looks like it was align bored at one point, but engine guy says very little taken out, should not effect rear seal. Did notice some small pitting on the crank journal main, so we bought a new crank, seal, etc. and did it again. Still leaks. Engine guy then does a FelPro offset seal, still leaks, and engine guy is perplexed, feels terrible, just cannot figure why it still leaks.

We just bought a NOS GM rear main seal off of E-Bay, thinking maybe somehow in today's world the FelPro seals are junk like a lot of current aftermarket things. We will have engine guy look at it and give his thoughts on next step, may have to pull the engine again and just tear it down, mic everything and come to some conclusion.

So, any thoughts on this, it really is odd.

Thanks.

[njsteve]

Crazy question but are you using synthetic oil?

When I had my Z11 (350/300) a few years back, I put over 1000 miles on the engine rebuild with conventional oil. Not a spot of oil anywhere on my garage floor.

After 1000 miles I changed the oil to the same viscosity synthetic (Mobil 1) and within 24 hours the oil drips started. They were seeping from the rear oil galley plugs near the camshaft.

Are you sure it is the rear main? The galley plug leak drips down to the exact spot where a rear main leak would be expected - around the pan joining surfaces. We had to pull the tranny twice and ended up having to epoxy the galley plugs in to prevent the leakage. We then went back to conventional oil.

[DRCBOWTIE]

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: njsteve</div><div class="ubbcode-body">Crazy question but are you using synthetic oil?

When I had my Z11 (350/300) a few years back, I put over 1000 miles on the engine rebuild with conventional oil. Not a spot of oil anywhere on my garage floor.

After 1000 miles I changed the oil to the same viscosity synthetic (Mobil 1) and within 24 hours the oil drips started. They were seeping from the rear oil galley plugs near the camshaft.

Are you sure it is the rear main? The galley plug leak drips down to the exact spot where a rear main leak would be expected - around the pan joining surfaces. We had to pull the tranny twice and ended up having to epoxy the galley plugs in to prevent the leakage. We then went back to conventional oil. </div></div>

Using Brad Penn 10/40, galley plugs bone dry. It is the rear main seal leaking. Thanks.

[PeteLeathersac]

Like Steve says, best be sure it's not something else leaking.
Common culprits that mimic rear main leaks are rear intake seal, dizzy base also oil pressure sender or fitting/lines for oil gauge.
Good luck!
<<GRAEMLIN_URL>>/beers.gif
~ Pete

[DRCBOWTIE]

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: PeteLeathersac</div><div class="ubbcode-body">
Like Steve says, best be sure it's not something else leaking.
Common culprits that mimic rear main leaks are rear intake seal, dizzy base also oil pressure sender or fitting/lines for oil gauge.
Good luck!
<<GRAEMLIN_URL>>/beers.gif
~ Pete

</div></div>
Intake, oil sender, oil line, galley plugs, oil pan, everything checked, bone dry. Leak is from rear main seal, 100% sure of that.

[PxTx]

Any chance you've got the wrong PCV valve or config creating too much pressure down below?

[SS427]

It may sound really stupid and or simple but is the PCV system hooked up? If not the crank pressure will push lots of oil past the rear seal under very heavy loads but will still leak just from idling.

[DRCBOWTIE]

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: pxtx</div><div class="ubbcode-body">Any chance you've got the wrong PCV valve or config creating too much pressure down below? </div></div>

Good point, I will check that.

[SS427]

Sorry about the double suggestion. I started my post before Paul and then got interrupted so I did not see that he had already posted that. Hopefully you figure out what is going on.