rear main seal - revisited

[John G.]

I was just in the archives searching out info on rear main seal leaks. Here is what's going on:

My engine (327) is a fresh rebuild. The oil leak problem was first discovered during initial engine break-in. This was during the 20-minutes-at-2000rpm run-in to break in the cam and lifters. The oil leak is fairly consistent; a drop about every 45-60 seconds. The rear main seal installed in the engine is the one that comes in the Fel-Pro rebuild gasket kits.

I'm thinking along the lines that kind of leak rate this might seem to suggest a 'pressure' leak - hence the rear main seal. Does this sound right? .. .

Where indicated in the shop manual I put sealer between the mating rear bearing cap and block halves. The angled rear main crankshaft seal lips face inward.

The rear main seal halves were installed about 1/8 inch 'offset'; not flush-on with the block and rear main cap surfaces. One end of the seal is up inside the block (1/8") with the corresponding other seal end protruding below the block surface. The mating cap seal half was installed in a similar fashion to accomodate the upper block seal half. Could this be a problem? . .. Is it not advisable to do this? . .

When removing the upper seal from the block (engine in car), how best to do this? .. I see there is a special tool that inserts into the drilled crankpin oil passage to accomodate rotating the upper seal out. Can a standard bolt be used, instead? .. .

I purchased the GM 10121044 rear main seal in hopes that this will take care of the problem.

I read some good helpful info in the archives. Any further comment, or tips and tricks that you guys might have up your sleeve would be a real help.

I'm hoping to do this ONE time and be done with that leak! .. ..

John

[Joe L.]

Re: rear main seal - revisited

John-----

Rear main seals on Chevrolet engines with 2 piece seals can be problematic. This has been true since the first one was built right up to the time that the last one was built in 1987. You don't think that GM went to the expense of completely redesigning this for the 1987 model year (small blocks) to use a 1 piece seal because the 2 piece seal worked just as well, do you? In any event, you should be able to get a reasonably good seal with the 2 piece even though you probably won't get a 100% leak-proof seal. You should, at least, be able to get to the point of no active drip.

The upper seal half is easily removed from the block (especially if it hasn't been in there a long time which is certainly the case with yours). You can use any suitable tool to press on the end of the seal, it will force it around, then you can grip it with pliers and pull it all the way out. Very easy. Make sure you use the little plastic "shoe horn" that usually comes with the seal to install the upper seal half. You don't want to cut the rear of the seal with the sharp edge of the block when you install it. The "shoe horn" prevents this.

The "offset" seal ends is a very commonly employed installation procedure. It should cause no problems.

The GM #10121044 seal should be exactly the same piece as the one that came in the Fel-Pro kit. I believe that Fel-Pro manufactures these for GM. In fact, I've used Fel-Pro seals that even had the GM part number embossed on them (much to the "dismay" of GM, I'm sure).

In order to get a leak free seal you've got to get the seal installed PERFECTLY and with sealer as described in the service manual. Also, the crank seal surface has to be perfect. If it's worn IN ANY WAY, scratched, or otherwise damaged it won't seal properly. Period.

Another thing: you should prime the engine before starting it and rotate the engine by hand while it is being primed. If the engine is started with the seal "dry", it may destroy itself in the first few seconds of engine operation. Check the seal lip of the one you remove to see if it suffered any damage.

[Wayne P.]

Re: rear main seal - revisited

Your description makes me think you may have the seal installed backwards. Is the open or closed side of the seal toward the front of the engine.

[Bill S.]

Re: rear main seal - revisited

Hope this helps you out:

http://www.corvettehacks.com/article5.html

Bill Schroeder




Corvette Hacks

[John G.]

Re: rear main seal - revisited

Joe ...
Thanks for touching on those important points you mention. That's interesting that the Fel-Pro and GM rear main seals had the same part number embossed on them. I guess that's how it is with modern day economics and company downsizing/consolidation. The new GM rear main seal I have doesn't appear to have any special feature(s), other than its tan color. I believe the Fel-Pro seal in the engine was black.

I will definitely check the old seal to try and determine why it failed. I have an oil pump primer tool to put to use for pre-lubing the seal. Great point!

Wayne ..
So as not to have any leak problem I tried to be real careful everything was just so when it came to installing that rear main seal - and making sure the lip seal faced inward. With the leak, and now second guessing, I hope I didn't goof.

John

[Joe L.]

Re: rear main seal - revisited

John-----

While the particular Fel-Pro sourced seal I used had the GM part number on it, that does not mean that both pieces actually have the same part number. I think that the one I got was a "mistake". In other words, when Fel-Pro was packaging seals under their label, they mistakenly used some of those they had made for GM. However, it did tell me that they are at least one of the manufacturers of the part for GM; there's no other way a seal with a GM part number could have gotten into their package. It's also very possible that someone else manufactures this seal for Fel-Pro, GM, and others. So, the mistake might have originated somewhere else besides Fel-Pro. No matter; it simply indicates that the manufacturing source is the same for both seals.

You can be sure that GM NEVER actually manufactured these seals or any of their predecessors. It's just not the type of part they would typically ever have manufactured in-house, let alone manufacture today.

The Fel-Pro seal is their number 2912.

[Clem Z.]

most seals leak after the engine shuts down

because the oil pressure from a running engine should force the seal lips against the crank. i have found the best solution to a leaking rear seal is 2 grooves machined into the lower bearing shell to allow the oil to run back into the pan when the engine is shut down. i did this to all my boat engines because any oil leak is a PIA in a boat. if it leaks while it is running you have a different problem