[DaleO]

Hi guys. I have two Pontiacs with what appears to be a leak in the same location. Both are '69, a 400 and a 428. They're leaking from the rear of the oil pan and crank location. I'm tired of the drips. Am I looking at an oil pan seal or main? Is this a chronic issue or just with my two?

[steve25]

At some point all rear main crank seals will start to leak, and even if it’s just a rear oil pan gasket leak the motor should be yanked to do it right .
To do the rear main crank seal the motor must come out and a whole lot more work needs to be done.
The good news is if you install a one piece type seal it will never leak again if done right, but these one piece seals are a two man job just so you know.

[Oldgoatnuts]

My 400 was leaking there and fortunately turned out to be just that the oil pan bolts had loosened, especially the two closest to the seal. It would be worth checking those. Good luck

[78w72]

1969 uses the early style single bead rubber "U" gasket on the pan that are prone to leaking. most people replace that seal with a 1/4" thick cork gasket, there should be info on here or other places on the web showing how to do it.

i had a leak in that spot on a new stroker build that i used a milodon pan with that early rubber seal, i installed the pan & the rest of the top end of the motor, after about 50 miles i noticed some spots on the ground & thought for sure it was the rear main seal that the shop installed with the short block, they had me bring it back to replace the main seal (BOP) & they installed the pan this time... it leaked far worse than when i did it, 6" spot on the ground after running for a few minutes with no driving! (my install was better than theirs!) so i got to pull the motor again & bring it back to the shop & this time i brung the cork gasket after talking to a pontiac builder mr p-body (sure do miss him around here) & he said its probably the rear pan gasket & to use the cork gasket with ultra black rtv sealer. sure enough after reinstalling the pan with that gasket its dry still after 5+ years & lots of miles & drag strip time.

if its the original rope main seal on the engine that could be whats leaking so you need to determine where the leak is before going further. can also look into the graphtite rope main seal that can be done with engine in the car, or pull it for a BOP main seal & cork pan gasket. & as a last resort, some guys have luck with the additives for rear main leaks but most are for rubber seals so thats a crap shoot & just a band aid for a leak.

best of luck!

[DaleO]

Originally Posted by Oldgoatnuts

My 400 was leaking there and fortunately turned out to be just that the oil pan bolts had loosened, especially the two closest to the seal. It would be worth checking those. Good luck

I did think of this and snugged up all the bolts evenly. Didn't work, sigh.

[John Milner]

If you pull the engine, bite the bullet and do both. I had one that dripped and I pulled the engine to just change the gasket. I put the engine back in just to have the rear seal continue to drip. I took it back out again and fixed the seal. The new one piece pan gaskets are worth the extra expense. I hear the new rubber rear seals are nice though I’ve always just used a quality rope seal. If you go back with a rope seal, I would highly recommended a “Best” brand rear seal. It is a night and day difference on the quality of them vs ones that come with felpro gasket kits.,

[DaleO]

Originally Posted by 78w72

1969 uses the early style single bead rubber "U" gasket on the pan that are prone to leaking. most people replace that seal with a 1/4" thick cork gasket, there should be info on here or other places on the web showing how to do it.

i had a leak in that spot on a new stroker build that i used a milodon pan with that early rubber seal, i installed the pan & the rest of the top end of the motor, after about 50 miles i noticed some spots on the ground & thought for sure it was the rear main seal that the shop installed with the short block, they had me bring it back to replace the main seal (BOP) & they installed the pan this time... it leaked far worse than when i did it, 6" spot on the ground after running for a few minutes with no driving! (my install was better than theirs!) so i got to pull the motor again & bring it back to the shop & this time i brung the cork gasket after talking to a pontiac builder mr p-body (sure do miss him around here) & he said its probably the rear pan gasket & to use the cork gasket with ultra black rtv sealer. sure enough after reinstalling the pan with that gasket its dry still after 5+ years & lots of miles & drag strip time.

if its the original rope main seal on the engine that could be whats leaking so you need to determine where the leak is before going further. can also look into the graphtite rope main seal that can be done with engine in the car, or pull it for a BOP main seal & cork pan gasket. & as a last resort, some guys have luck with the additives for rear main leaks but most are for rubber seals so thats a crap shoot & just a band aid for a leak.

best of luck!

Thanks for this. At this point it is not such a big deal for the 428 as I am planning to change the cam so can do the fix then. The 400 does not leak as bad so will live with it and a piece of cardboard for now.

thank you guys,
steve25,
Oldgoatnuts,
78W72,
John.

-dale