I'm now on my second 2912 fel pro rear main seal on this engine and I still have a leak. On each install I followed the directions carefully off setting the seal 3/8" and being careful not to shave the back of the seal when it goes in, using rtv on the proper place on the mating surface of the bearing cap near the seal. Then torquing to 20 ft/lb and moving the crank foward and aft to center the bearing cap, but still have a leak.
I have one seal that I removed and did not inspect it closely until I replaced it and developed another leak.
To back up a little I noticed on the bearing cap on the second install that there is a "nub" of metal sticking out onto the edge of the area where the seal sits. I I thought it might be a flaw of some sort but on close inspection it is very symmetrical and appears to part of the rear cap. So I figured maybe it's to keep the seal from rotating on cold starts or something?
In any case on close inspection of the rear main seal that I removed I found this.
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It appears to have a small hole in the edge of the seal. The hole does not goe all the way through into the inner surface. I also notice this just above that puncture.
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This would be where that "nub" is pushing down on the edge of the seal. It seems obvious that this should not be happening and may be the cause of my leaks. It also appears to be causing the seal to oval some what by looking at the sear on the mating line.
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Anybody else ever run into this? Am I on the right track here? My plan, if I am , is to remove the little "nub" of metal with a dremel tool. Any other suggestions or reasons this could be happening.
This is a fresh rebuild and the rear bearing is new as is the crank and both are within spec as far as size and oil clearances.

 

I did that work last year. This is the procedure I used:

http://www.corvettehacks.com/article5

I think offsetting the ends of the seal helps. I also used the lip seal that is offset. My vette has 120k now and the original has cut a groove in the crank. The lip on mine is offset to the rear.

Applying silicone to the main cap faces helps too. See the black and white pic.

I took my vette to Bowling Green after I did this work. No leaks. It can be done.

 

Are you absolutely sure it's the rear main seal causing the leak? There are other areas above the rear main seal that can leak e.g. cam plugs.

 

Did that procedure exactly, I also moved the crank to center the bearing cap although this would have no effect on the sealing just bearing wear.

area above the seal is dry. no leaks from block plugs. Also not coming from valve covers. I jacked the car up, put it on blocks, started the engine and watched the oil drip from the rear main seal. Not the pan gasket either it is wet above the pan gasket at the main seal.

Not thought on the little nub of metal on the bearing cap? I need to get a pic. First I have to take it apart again.

 

IMHO, the ovality of your seal is certainly the problem. That seal should firmly seat all the way into the block and the cap relatively easy. I have never seen a noticed on a cap before. Use a very thin coat of sealant between block and cap, I think silicon is too thick, permatex anaeorbic selant would be a better choice. Make sure the seal lips face into the block and offseat ends like you have been doing and make sure you oil the lips of the seal so you do not burn them on start up.

 

Quality control on auto parts [probably true for everything, these days] is very "suspect". When I pick up a part, I alway open any box/bag to inspect the part right there in the parts store. That way, if there is a defect, it can be observed by the store personnel immediately and a better replacement procured, without any hassle.

Can't tell you how many times that has saved car miles and "hassle" grief.

 

If that is what is happening due to the nub pushing down on the seal then I would agree with you.
I have only tore down three SBC's. Two a 350 (this one and one 25 years ago) and one a 400. The 400 did not have any such nub of metal on it.
I can't find anywhere where this is supposed to exist. I suspect this is the issue. I wouldn't have even noticed it if I didn't have to replace the seal repeatedly.
Been using a product called Yamabond. It is used to seal two stroke motorcycle engine haves together. It goes on very thin. It does not show signs of letting oil by or holding the cap away from the block. 70 ft/lbs would probably take care of any excess glue.
LOL!! isn't that the truth. In this age of world economy, quality control is definitely suspect. Although in reality it always has been, could be I just notice it more now.
On these seals I wonder how the ends are to seal together. Just looking at them it seems unlikely. Yet instructions are specific about NOT using RTV glue on the ends.

 

First u say u use RTV then u post Yamabond between the block and cap? Don't know what Yamabond is but u need to get a thin runny anaerobic sealer as mentioned.

Did u offset the mating lines? This means the seal mating line does't match the cap to block line. U have to push the seal up a little and let the other end hang out some - not alot but maybe at least a 1/4". And on the ends of the seal i put a tiny amount of RTV there to get the seals to bond.
Take your time and sort it out so u don't get sealer all over the seal.
Oh and make sure u wet the seal with oil before install - don't install dry. But leave the mating ends dry to apply the tiny amount of sealer there. Take time and sort it out i know u will get it Reel.

Good luck,
cardo0

 

The ends of the 2 seal halves are supposed to fit together tightly enough that they won't leak. Then, if you offset the joint between them (by rotating the upper half of the seal about 1/4" from being 'flush' with the cap splitline), that juncture is NOT at the same spot as the splitline...thus, enhancing sealability.

If you want even further comfort, put just a small dab of Black RTV sealant on the ends of the upper half of the seal, just before inserting the lower half and cap. You don't want so much sealant that it will spread out to the sealing lip. Just enough to improve the sealing of the seal BODY pieces. Be sure to wipe the ends of those seal halves with lacquer thinner before adding the RTV dabs.

Note: Other 'silicone' sealants should NOT be used to seal oil. Black RTV is the only silicone product that I know of which is formulated for sealing oil and actually WORKS.

 

I'm watching this with interest as my rear seal has been weeping for years. It is the next task for my '73.

I had not heard of the Felpro 2912 seal but sure enough found it at Autozone for the high-performance sbc. My engine is not high-performance and found that Autozone also has the following for sbd: Felpro BS40655 (single lip), BS40013 (double lip) and BS11829-1 double lip improved design. BS40013 is the one I selected but I have seen a recommendation for BS11829-1 (the improved design).

The metal protrusion on the bearing cap (A design feature, or defect?) is an interesting question and may be impacting your experience with the seal.

 

Yes! Thank you, that is my question.

Yamabond is a thin flowing RTV. It has superior properties to Ultra black by permatex in areas where clearances are tight. Thanks for the vote of confidence. This is the kind of stuff were I don't know if that little protrusion should be there or not since I have nothing to compare it to. Logically I would say it should not be there.

I'll tear into this thing again this weekend and get a pic of that little protrusion on the bearing half.
If you look at the pics of the seal again I think you'll see that the seal is damaged in that area. It looks to me like it was pinched or folded over by the bearing half nub of metal. Should have more evidence one way or the other once I take out the seal that is in there now.

 

You have installed the seal in the proper direction, I assume?

I don't recall any kind of "indexing tab" in the seal recesses for the end/bearing/seal caps. Unless there is a mating notch in the seal for it to engage, it should be eliminated before installing another.

 

Yes, both installed in right direction. Big lip forward. Also left 3/8" sticking out on one side which leaves the other side recessed 3/8" so that it has a different mating line than the bearing cap.
I agree that the "indexing tab" as you say, should be removed.

 

Had some time today so I decided to take off the rear main bearing cap. Good news is I'm getting really good at this, faster each time.
Here is the offending little bump on the bearing cap. I'm a little embarrassed about this. After taking a good close look at this it is pretty obvious that this is no design feature. It looks like a bit of welding slag bonded to the surface. I tried to just pick it off with screw driver but it's not budging. Guess the dremel will get it.

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How or when it got there I don't know. It may hve been there on tear down. I did notice that the PO had used plenty of rtv on the old seal to get it to seal up when I took it apart. Just figured it was a bubba thing or something. Didn't know there might actually be problem.

 

That's a nasty little bugger.

 

That needs to be ground/stoned/filed flush so there is no "proud" metal on the inner diameter nor the side-surface.

 

I'll see what I can do to get it smoothed out.

 

Looks like someone hit it with a punch/hammer...maybe trying to get an old seal out....

 

In the second pic it does look like a divit in the metal but it's flush with the surface. No metal has been moved around it's been added. Like I said looks like welding slag or something.

 

Got it smoothed out today. should work pretty good I think. Looks like this now.
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What is your opinions on this little corner of the bearing cap? I think this is where the welding slag came from. Looks like a functional repair, even though not perfect.

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I'd say mystery solved as to where that little bump of metal came from.