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There have been many conversations on the Rear Main Seal for Pontiac's. When I bought my car the Rear Main Seal leaked terribly. (It was the rope style) I removed the engine and replaced with Viton (Lip Style) Rear Seal. Still had significant leakage. Removed engine again and replaced with Graph Tite (Rope Style) Seal. Did not leak until after about five minutes. Leaks now as bad as the previous seals. I really do not know what to do at this point. All seals were installed following instructions to the letter. Any ideas??
Thanks
 

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There have been many conversations on the Rear Main Seal for Pontiac's. When I bought my car the Rear Main Seal leaked terribly. (It was the rope style) I removed the engine and replaced with Viton (Lip Style) Rear Seal. Still had significant leakage. Removed engine again and replaced with Graph Tite (Rope Style) Seal. Did not leak until after about five minutes. Leaks now as bad as the previous seals. I really do not know what to do at this point. All seals were installed following instructions to the letter. Any ideas??
Thanks
Any nicks on the rim of where the seal is installed? Burrs maybe? Is the casting in that area in some way damaged? Did the sealant properly cure and set before installation was finished? Buddy had a vitron seal installed in his '67 GTO over the winter, the engine was jacked up not removed for the process..... its leak free.
 

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Did you remember to change the seal on the full moon and to sacrifice a goat beforehand? :D

Seriously, getting these things to seal at the rear main for some reason continues to be a hit or miss proposition no matter what you try. I've got a Viton seal in my 461, which I installed myself with meticulous attention to detail. I discovered on the Power Tour that it's going to lose about a quart with every tank of gas, running at highway speeds all the time. Cruising around town, it's mostly ok. My next one's going to be a Graph-tite whenever I decide to do it.

The smart move is to test the seal before you re-install the motor. Put it together, fill it with oil, then rig up a way to tilt it back at a steep angle - enough to make sure the seal is completely submerged in oil - and let it sit for a couple of days while you visually watch for leaks. Don't put it back into the car until you're sure it's sealed.

Bear
 

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somewhere, there is a surface that's not right. that should not fail over and over no matter what type of seal being used.
 

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There is a lot of information out there on these seals and the sealing areas. The main concern seems to be making sure that the crosshatched area of the crank journal does NOT come into contact with the lip of the seal, with a VITON seal. If it does, it will leak. Another concern is the trueness of the rear main cap and saddle area. If extensive machine work has been done (line boring or line honing), this area can end up out of true and out of square, and the seal can be a leaker. I've installed several VITON seals, and have gotten lucky. They've held up leak free for several years and many thousands of miles. This is a hugely labor intensive job, and is no fun at all, especially if you have to keep re-doing it. I would carefully inspect the entire rear main area for flaws.
 
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