oil pouring through rear main seal

[MidLifer]

I recently got done with putting a LQ4 into my 71. When it first started up, it started pouring oil out the rear main seal. Figuring it was rear cover alignment, I bought the AlignIt tool from Sac City Corvette, followed the instructions and replaced the seal. Leaked again. Removed PCV hoses, oil cap and dipstick, no change.

I did the whole procedure one more time, making sure the crank was clean and dry and I was putting the seal in the right way (being able to see "this side out"). Even put a dial gauge on the crank to see if it might be bent, only saw 1/1000 of runout. Stuck a micrometer between the cover and the crank after installing the cover and measured less than 2/1000s of difference all the way around.

Same leak happened when I started up the engine.

It does not look like it is leaking through any of the cover bolts. When I look behind the flexplate I see the oil coming out from the bottom of the rear main.

I've read every thread I can find here and on other sites about this issue. I would suspect crankcase pressure, but wouldn't taking the oil cap off relieve that? Also I did not feel any air coming out the filler hole with the engine running.

I'm not using a turbo, this is a stock engine.

What should I try next?

[LeesTruk]

Has the rear plate been removed from the engine, as far as you know? There are a couple of oil passages that are sealed by this plate, and if the gasket has fractured, the engine will bleed oil profusely

[MidLifer]

I removed the rear plate and put a new gasket on it each time. I've been using the FelPro seal kit BS40640 which comes with a new cover gasket.

The leakage starts a few seconds after the engine starts and you can hear a hiss as the oil goes past the seal, which I why I'm suspecting crankcase pressure. But what has me scratching my head is that opening up the dipstick and oil cap doesn't change things.

This is the tool (AlignIt tool by SacCityCorvette) and procedure I've used for removing and replacing the cover/seal:

https://youtu.be/gfAR_fy8zCU

[LeesTruk]

Yeah, I have that tool, too. Used it when changing the cam in my 5.3L. If it is internal pressure, though, wouldn't you think it'd be blowing out the front seal, also? We had a fellow at the shop replacing the rear seal on a Silverado 6.oL, and he boogered the oilpan gasket taking off the rear plate. Ended up having to drop the pan to replace that gasket too. There is a TSB, from Chevy, concerning block porosity, but that is for Aluminum block 6.0's.

With the engine running, and the dipstick and oil fill cap removed, can you actually feel any pressure escaping from these openings? If not, I would start looking for a mechanical reason for the noise (metal on metal type rub)

[MidLifer]

Thanks again for the response. I feel nothing escaping from any of the orifices. The sound is definitely coming from the rear main area, and sounds like liquid and maybe gas being pushed through a tight space.

Just to rule out head gasket or other issues, tonight I'm going to do compression and leakdown. If those come up clear, then I'll buy a new rear cover and seal kit. Maybe the cover itself is warped and the high-pressure passage at the top is leaking. While I have it off I'll also check the oil filter barbell to be sure it's there and in the right place.

[crazy longhorn]

Did you use lock tite on the flex plate bolts? Understand, that the bolts go all through), & will leak if not sealed with a thread locker ....just a thought One other thought....I got my rear cover from a GM dealer, gasket seal & all. The seal had a sleave in it, to keep the "lips" oriented properly.....slid right on, & no issues& about the price that you spent on the aftermarket pc from Dorman! I did also replace the "barbell", when I was there....hope that helps, crazy L

[MidLifer]

Thanks for the thoughts. My local GM dealer wanted 2x what I paid for the Dorman piece, guess I need to shop around a bit. Also, the seals I am using (Felpro) are the ones that GM puts in at the factory. Felpro admits as much on their website.

Did the leakdown last night - the tester my buddy lent me was the HF one so the gauges are for s*** but I was able to pressurize the cylinders and see where the air came out. Nothing out of the usual, just a little blowby past the rings. Ran compression too, 210+ in all cylinders. So I don't think I'm dealing with a pressure issue and as LeesTruk pointed out it isn't blowing out of any other seals, so I guess I have to keep trying til I get the seal right.

Thanks all, this board is the best money I spend on my hobby.

[bandit0067]

Are you 100 % sure the seal is not in backwards......they will go in that way.... and only use motor oil to lube, no lithe grease or any super slickem lube.

[akdg87]

how is your PCV set up?

[MidLifer]

I am 1000% sure the seal is in right. I can see the "This Side Out" on the seal.

PCV is embedded in the valve cover like all truck LS engines and is not blocked. Has a vacuum line to the intake, then another line from the TB behind the butterfly to the other valve cover. "Clean and dirty sides" as they say.

[akdg87]

positive its the rear main and not the cam position sensor leaking?

I have seen LS engines where the oil puddles up where it goes into the block and looks just like a rear main leak. O ring gets wore out and oil makes it way by.

[MidLifer]

I’m running the engine with the transmission off. I can see and hear the oil coming out of the lower part of the rear main seal behind the flexplate. Even dyed it and used a uv flashlight. I am as sure as my middle-aged eyes can make me.

Originally Posted by akdg87

positive its the rear main and not the cam position sensor leaking?

I have seen LS engines where the oil puddles up where it goes into the block and looks just like a rear main leak. O ring gets wore out and oil makes it way by.

Posted via Mobile Device

[akdg87]

Originally Posted by MidLifer

I’m running the engine with the transmission off. I can see and hear the oil coming out of the lower part of the rear main seal behind the flexplate. Even dyed it and used a uv flashlight. I am as sure as my middle-aged eyes can make me.


Posted via Mobile Device

From LS1 tech: https://ls1tech.com/forums/generatio...l-install.html

"I am a Chevrolet tech. and when the new design seal came out i installed several and each eventually leaked, the reason was i installed them flush with rear seal cover. Turns out they need to be bottomed out in the cover, i have used the proper Kent moore tool but prefer to self center seal and torque in place."

[MidLifer]

So, looks like crazy longhorn called it. While getting ready to replace the seal the 3rd time, I noticed "spray marks" on the flexplate. So I put thread sealer on the bolts when I put it all back together and wah-lah, no leak.

Now it could have been the new cover or the 3rd seal getting it right, but I'm thinking I was just overlooking the bolt threads.

In any case, time to get the tranny back in and drive this puppy!

Thanks all!

[66 C10 383]

Thank you for the update and resolution of your situation. Great Info. I'll keep an eye out for this when I eventually get around to doing this.