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BBC rear main leak

General engine tech -- Drag Racing to Circle Track

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allencr267
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Re: BBC rear main leak

Post by allencr267 »

rgalajda wrote: Fri Nov 18, 2022 6:51 amSomething wrong here?
Believe that's just a photo optical thing, the seal is offset, parting line.
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Re: BBC rear main leak

Post by AA Performance »

allencr267 wrote: Fri Nov 18, 2022 10:07 am
rgalajda wrote: Fri Nov 18, 2022 6:51 amSomething wrong here?
Believe that's just a photo optical thing, the seal is offset, parting line.
Yes, optical thing. Can anyone see the sealing EDGE isnt there on one side, didn't think the picture was that bad. Leak has nothing to do with the silicone
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Re: BBC rear main leak

Post by Dave Koehler »

AA Performance wrote: Fri Nov 18, 2022 7:41 pm
allencr267 wrote: Fri Nov 18, 2022 10:07 am
rgalajda wrote: Fri Nov 18, 2022 6:51 amSomething wrong here?
Believe that's just a photo optical thing, the seal is offset, parting line.
Yes, optical thing. Can anyone see the sealing EDGE isnt there on one side, didn't think the picture was that bad. Leak has nothing to do with the silicone
You don't think that big wad of silicone on one side and little on other has anything to do with it?
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Re: BBC rear main leak

Post by AA Performance »

Dave, are you able to ENLARGE the first pic to have a good look at the edge of the seal in the corner? I know you can see the silicone but what about the problem area that I have mentioned many times? The sealing edge is not there. Its not that the silicone ate it away. Seems you must have had a bad experience with silicone some time. Do you know how much silicone was put on the mating face for it to spread? Do you see any silicon on the sealing edge that may be the issue? Do you think that perhaps ALL that silicone has distorted the seal and block or something?
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Re: BBC rear main leak

Post by Dave Koehler »

I have blown it up larger than the forum allows.
I think most of us see in the second photo a big gob of silicone in the seal cavity holding the seal away from seating on the block.
There is also seen some silicone behind the main seal lip which might not allow the lip to flex normally.
So yes, distortion is a real possibility.
Install a new seal without silicone to prove your diagnosis.
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Re: BBC rear main leak

Post by 1972ho »

I know I made a couple of mistakes about main seal leaks that I thought were leaks twice and and after a couple of replacement it turned out to be main oil gallery plugs leaking and dropping right down on the area of the seal.
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Re: BBC rear main leak

Post by rp930 »

Felpro: STEP 5
Put a tiny dab (1/8" or smaller) of RTV on each end of the lower seal, where the seal ends meet, taking care to avoid the sealing lip. Less is better in this case.
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Re: BBC rear main leak

Post by AA Performance »

Dave Koehler wrote: Sat Nov 19, 2022 8:23 am I have blown it up larger than the forum allows.
I think most of us see in the second photo a big gob of silicone in the seal cavity holding the seal away from seating on the block.
There is also seen some silicone behind the main seal lip which might not allow the lip to flex normally.
So yes, distortion is a real possibility.
Install a new seal without silicone to prove your diagnosis.
All you say isn't a problem or issue and has nothing to do with the leak 100% because the leak was from the other side were the sealing edge isn't touching the crank. As you said , that "BIG" gob is in the hollow cavity of the seal and isn't distorting anything. I must be sounding like a recorder as I seem to be repeating my self over and over. Dave, do you understand what I'm trying to show you? I'm not asking were the issue is, I'm telling you but it seems your not seeing it. [-o<
I have installed another seal to replace the faulty one and it smoke tested fine and it had a sharp sealing edge were the other one was missing at the corner. PS : I used twice as much silicone all over to make sure \:D/
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Re: BBC rear main leak

Post by Tom68 »

AA Performance wrote: Sat Nov 19, 2022 8:04 pm PS : I used twice as much silicone all over to make sure \:D/
There wasn't that much there the first time, shit spreads, best it spreads to the outside of the engine.
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Re: BBC rear main leak

Post by AA Performance »

Tom68 wrote: Sat Nov 19, 2022 8:43 pm
AA Performance wrote: Sat Nov 19, 2022 8:04 pm PS : I used twice as much silicone all over to make sure \:D/
There wasn't that much there the first time, shit spreads, best it spreads to the outside of the engine.
Thanks Tom, someone that knows at last. You must be an engine builder as well.
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Re: BBC rear main leak

Post by rp930 »

I get what you’re saying but it could have affected the way the two seals meet and created a problem. I guess we’ll never know. Never been a fan of silicone in an engine. Sorry.
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Re: BBC rear main leak

Post by AA Performance »

rp930 wrote: Sun Nov 20, 2022 4:48 pm I get what you’re saying but it could have affected the way the two seals meet and created a problem. I guess we’ll never know. Never been a fan of silicone in an engine. Sorry.
As previousley stated, Felpro recommends silicone on the 2 joining faces and the block. How would it affect how they match up? If you use a ton of silicone, then all that silicone will squeeze out anyway, unless your one that lets the silicone go off before fitting.
Last time, the seal leaked due to it being FAULTY. It had a fault in the corner of the SEALING EDGE. The SILICONE didn't have ANYTHING to do with the leak. Just letting you guys know so that you start inspecting parts a lot more closer before fitting as parts manufactures seem to have a crappy quality control section now a days.
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Re: BBC rear main leak

Post by In-Tech »

AA, I got what your were saying in the first post. I thought the same thing, good reminder to check EVERYTHING. Parts can always be made wrong or a simple flaw :(

p.s. I use flange sealant and bolt the rear cap on without the crank so I can check for distortion of the seal, in my experience 1 out of 10 rear seals are fubar.
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Re: BBC rear main leak

Post by jsgarage »

Some rear main seals work better if the seal lip is wiped with motor oil during assembly. Starting the engine with such a seal dry sometimes induces abnormal seal wear probably due to the thin lip sticking to the dry steel of the journal. On other main seals, the mfgr tells you to assemble dry. Best to follow directions unless you're trying to redesign something. I only use silicone on the sides of the #5 main cap, as mentioned.
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Re: BBC rear main leak

Post by Tom68 »

jsgarage wrote: Wed Nov 23, 2022 9:58 pm . On other main seals, the mfgr tells you to assemble dry.
Yer, I've had those, teflon or something. Hard to imagine lubing them causing a problem considering what they have to contend with, but used them dry, they look a lot different to a regular seal.
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