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455 Pontiac rear main seal leaking

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23K views 37 replies 24 participants last post by  tjs44  
#1 ·
Guys, im building a stock 455 for a friend of mine who's restoring a 72 Trans am. So im using the stock crank etc. I initally put this together with a rope seal because thats what came with the gasket kit, then i heard there was a more modern/traditional 2 peice type rear main seal available from allpontiac.com. From what i understand, there are few options for the rear main other than the oem rope seal or the seal linked below...

http://www.allpontiac.com/rearmain_seal.html

I decided to ditch the rope seal and use this 2 peice deal,... well lo and behold the phucking thing leaks.

I have it on my engine test stand and it doesnt start leaking till it gets to about 140deg, for whatever thats worth...

Ive built sbc and bbc's for 20 yrs and this is the first pontiac i ever screwed together... How are you guys sealing up the rear main seals on these 455's? Should i have stuck with the rope seal? What am i missing here?

Looking for info only from guys who are familier with Pontiacs!

Thanks fella's
 
#2 ·
Haven't run a 455 but have ran several 350 Pontiacs back in the day. I switched from the rope seal to the 2 piece seal and never had an issue with leaks. The only time I had an issue with a rear seal leaking like you describe when it gets warm was with a SBC. Was helping a buddy and he was supplying all the parts. After replacing the seal for the second time (after checking everything numerous times) and still having it leak I went to the store and picked up a Fel-Pro seal to use instead of the brand he had been buying. Replaced it the third time and no more leaks.
 
#4 ·
Hell, I always used the rope seal on 455's. Never had any problems with them leaking. It wasn't an all out race application but on the spray it probably made 700.
 
#7 ·
I have used a couple of the rubber seals in Pontiacs. I was told that the rope seals had asbestos, and it's not in the newer ones. I was told they are more prone to leakage without it (rope that is). Did you install the seal with the crank in or out? I installed them when assembling the engines. I had to put the seal in place and check the amount they stuck out of the housing bore (as the instructions said). I had to trim the ends to get them within specs. I ran them on my break in stand with no leaks.
 
#10 ·
I had the engine fully assembled (hadent run yet either) when we decided to change the seal out. I popped the caps off, lifted the crank a hair, rolled the new seal in and trimmed as the instructions said. It wasnt difficult at all, .020 thou on one side. Used a dab of silicone in the anti-rotation grooves and re-installed the caps.
 
#30 ·
I use this seal in my Pontiac engines with excellent results. http://www.bopengineering.com/beltdrive_acc_topend2.shtml

If installed properly will not leak. I also heard the Best seal was good too. There are 2 different sizes. I also used the new BOP 1 piece pan gasket on my new engine. Fit great but haven't run it yet.
I've used these very successfully. I order from Butler. Offset the seal about 1/4" Zero leaks, no vacuum pump, and 150 shot.
 
#20 ·
666 the legend[/B said:
.....I heard that FEL-PRO didnt make a rear main seal..for the 455 PONTICRAPS..?? humm..??
Shelton_Barrs said:
I quit running Pontiacs some years ago and never had a 455. Your right, Fel-Pro doesn't have a 2 piece seal for the 455. But if anyone needs or wants one, BOP Engineering has a nice looking Viton 2 piece seal for the 455.
The "old" seals like that were typically reworked Cadillac rear main seals,and yeah those were made to fit the "large main journal" pontiacs (421-428-455).

H-O racing used to sell a seal like that back in the day as I recall.

I had one in my 455 H-O GTO.

Back then there was no rear main seal alternative for the "small main journal" pontiacs (350-389-400).

The BOP seal is indeed an excellent piece,but some installs will always be problematic,and have trouble sealing with them for various reasons,so the new Best "graphtite" rope style rear main seal is another excellent option to have @ one's disposal.

Some pontiac cranks have "serrations" on the rear main sealing surface,and those can sometimes make it hard for those cranks to seal well with the modern "lip" style seals,and then there are also some blocks that wont have a perfectly "concentric" seal bore,and those too can be problematic with the more modern rear main seals.

For those engines the "graphtite" rope seals are the best choice.

I dont think the problem with the older rope seals was so much the loss of the asbestos in them,more so it was the change in the actual "weave" of the replacement rope seals after that change,they went from a fairly fine/tight/dense weave to a coarser/looser weave,and the later rope seal itself just didnt seem to seal as well as the earlier rope seals did.

But the "graphtite" rope seals are excellent by all accounts,and seem to be doing the trick for the engines that are'nt sealing well with the BOP seals,so between those two options one should be able to get their rear mains sealed up nicely.

2¢

Bret P.
 
#22 ·
I also use the BOP seal that is mentioned above in my stroked 400(461) pontiac,and have not had a ounce of problems with leakage. Now,on the other hand, I had a 455 before I built my 461,and I ran the rope seal in it(not the better rope seal w/asbestos),and always had problems with it leaking. I will never use anything else but the BOP seal,just from my past experiance.

Brian
 
#37 ·
I know this is a old thread, going to put my 400 back together, read lots of forums. I have had problems with the damn thing leaking oil from the rear main.... are these new teflon/graphite seals the way to go? or how are these 2 piece rubber ones working? this damn leak is driving me nuts....;(