rear main seal headahce - Team Camaro Tech
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post #1 of 22 (permalink) Old May 9th, 19, 04:20 AM Thread Starter
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rear main seal headahce

so i had a new engine built a couple years back and i've been chasing an oil leak since day one. it started relatively small at the rear of the engine and i exhausted all options and checked all possibilities of valve cover, china wall, etc....
finally bit the bullet and pulled the pan to replace pan gasket as i was convinced that was it. long story short, it wasn't the pan.



last option...REAR MAIN SEAL.


this time i pulled the transmission to make the rear of the block more accessible for inspection. dropped the trans, cleaned everything as best i could, blocked the car up real good and ran the motor without transmission so i could get underneath and watch it leak. sure enough, rear main seal.


went ahead and dropped the pan again to start in on seal replacement. then i found this.



it's hard to tell but the two halfs of the rear main seal were installed in opposing directions to each other. unbelievable that a reputable engine shop did this. I've been battling this leak for two years now all the while hoping that it wasn't the rear main. wish i would've just bit the bullet and done the main seal the first time i had the pan off.



like i said, it's been two years since engine was built so i'm not even going to bother going to the shop to show them what they did. it really sucks because my new ceramic coated headers are now covered with burnt oil on the collectors and i'm not sure if anything will take that off without damaging the coating.



just thought I'd share for the sake of venting. this was not fun.
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post #2 of 22 (permalink) Old May 9th, 19, 04:24 AM Thread Starter
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Re: rear main seal headahce

oh BTW, for the time being, i officially have a completely leak free small block chevy for what i'm pretty sure is the first time in my life.
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post #3 of 22 (permalink) Old May 9th, 19, 07:10 AM
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Re: rear main seal headahce

You can remove burned on oil from the ceramic coating by using a red scotch brite pad, with liberal amounts of mag wheel cleaner, have done it many times. It polishes up very well.
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post #4 of 22 (permalink) Old May 9th, 19, 08:30 AM
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Re: rear main seal headahce

That is the way a reputable engine builder installs the rear main seal so that it doesn't leak. You put sealant under the cap at the edge inside the seal but outside of the thrust collar and offset the seal so that it won't leak at the parting line.

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post #5 of 22 (permalink) Old May 9th, 19, 08:47 AM
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Re: rear main seal headahce

I have always understood "off setting" the 2 seal halves so they don't line up with the cap seam is the better way to install a RMS
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post #6 of 22 (permalink) Old May 9th, 19, 09:27 AM
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Re: rear main seal headahce

I have read pros and cons to both theories. (to offset or not to offset) At the very least some RTV should of been used.

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post #7 of 22 (permalink) Old May 9th, 19, 10:11 AM
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Re: rear main seal headahce

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At the very least some RTV should of been used.
I have always used Permetex black "ultra" RTV. More suited to high temp/oil sealing. Prep of mating surface (wipe several times with acetone), IMHO, is the way to clean then

2 piece RMS has always been prone to leaking and off setting seals has been the way I have always seen/done be it rubber or the old original type seal
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post #8 of 22 (permalink) Old May 9th, 19, 10:11 AM
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Re: rear main seal headahce

Did you reuse the old seal or install a complete new seal? I would have been tempted to use the old seal to avoid any chance of damaging the crank removing the correctly installed upper half of the seal from the block. The seal looks to be in great shape except for the cap half being installed backwards.

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post #9 of 22 (permalink) Old May 9th, 19, 10:40 AM
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Re: rear main seal headahce

Quote:
Originally Posted by SoCal805 View Post
I have always used Permetex black "ultra" RTV. More suited to high temp/oil sealing. Prep of mating surface (wipe several times with acetone), IMHO, is the way to clean then

2 piece RMS has always been prone to leaking and off setting seals has been the way I have always seen/done be it rubber or the old original type seal
No matter where you "offset it" you will have a split in the seal, a leak doesn't care where the split is. I'm not suggesting you do not offset it, I'm only making a comment here. I have changed the RMS on my last BBC 3x, I tried both offset and not offset. They all eventually leaked.

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post #10 of 22 (permalink) Old May 9th, 19, 11:15 AM
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Re: rear main seal headahce

yes a 2 piece seal will always have the split....not saying off setting it is a 100% never leak solution. It just takes the split away from the cap/block split location....which "helps" IMHO.

Scored crank where the seal rides, not "dead nuts" flat/even cap/block, poor engine balance will all have impact on RMS sealing...or not

I think the OP's issue was the cap 1/2 was backwards
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post #11 of 22 (permalink) Old May 9th, 19, 12:18 PM
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Re: rear main seal headahce

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Originally Posted by bhodgdon400 View Post
oh BTW, for the time being, i officially have a completely leak free small block chevy for what i'm pretty sure is the first time in my life.
Knock on wood.
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post #12 of 22 (permalink) Old May 9th, 19, 01:47 PM
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Re: rear main seal headahce

Learned about offsetting the seals like in the picture 30 years ago from my Dad. Never had any issues. But I also never put the seal in backwards like the one on that cap. Ooops.....
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post #13 of 22 (permalink) Old May 9th, 19, 02:22 PM
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Re: rear main seal headahce

you should also use a dab of rtv on the seal ends as well. I use a q-tip with alcohol to clean the ends before applying the RTV.
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post #14 of 22 (permalink) Old May 9th, 19, 07:03 PM
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Re: rear main seal headahce

You guys are all missing whatís in the picture. Look closely at the pictures. The half of the seal that is installed in the main cap was installed backwards with the seal lip facing towards the back of the block. The other half of the seal that is under the crank is installed correctly with the lip facing in towards the center of the block. An amateur mistake that caused a big headache and made a mess. Ben, at the very least, I would show them the pictures and express your disgust with the builder. It must at least feel good though knowing that YOU finally found and fixed the problem. I hate leaks personally, especially oil leaks.

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post #15 of 22 (permalink) Old May 10th, 19, 06:10 AM Thread Starter
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Re: rear main seal headahce

Quote:
Originally Posted by bill3337 View Post
You can remove burned on oil from the ceramic coating by using a red scotch brite pad, with liberal amounts of mag wheel cleaner, have done it many times. It polishes up very well.



thank you. i will try that
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