The Stovebolt Site Forums The Shop Area Engine Shop 53 GMC main seal leak

I have 53 GMC with an original 302 six that I rebuilt and the old rope seal was too loose and leaks right out of the gates, (in other words, as soon as I started running it) This is my main truck and I have been running it for a few years spewing oil all over the place. Any ideas for fixing it? Are there any new different types of seals that would replace the old rope style and would make pulling the engine again worth it?

If you mean that you have to pull the engine to replace it, that is not strictly true. There is a quick way of doing it, in the tech section which may or may not work for you. Another method is to remove the transmission, oil pan, front cover and lower pull the crankshaft down with the rods still attached. That gives enough room to do a conventional type replacement.

Thanks Truckermix, I know that one can do an inplace replacement of the rear main, but in practical use, I have found that it is difficult to do well. I know how difficult it is to do it on a stand and get the pan gasket well placed and sealed. My main concern is that I get a seal that is going to seal. I used the standard rope seal and it was too small. I know cause I made the mandrel that is specified on the shop manual to drive the seal in and used a razor to trim it. When I used the mandrel the seal went in too easily. I know that the inline sixer race moter guys usee this engine and I wonder what they use when they build their high performance engines. Thanks again, Juan

Juan, the problem isn't with the type or size of the seal, it's the method of installation. Granted, it's difficult to do a seal replacement with the engine installed, but not impossible. The trick is to soak the original-equipment type seal in motor oil for quite a while, even overnight isn't too much, roll it into a long, too-small diameter, fish it over the upper side of the crankshaft, and then pack it firmly into place before it's cut to size. Do the same thing with the lower seal half in the bearing cap, and trim the ends only enough to prevent them from interfering with torquing the bearing correctly. I've done it numerous times, on all sorts of vehicles. The procdeure is just about the same, regardless of what vehicle is being repaired.
Jerry

thanks for the additional info, it all helps, Juan

A great tip I had from a rebuilder was to install the neoprene seal so that the seams do not line up with the block/cap joint. In other words the block/cap joint runs (like clock hands) from the 9 to the 3. If you tilt the seal to the 10 to 4 position you are adding more security against leaking. its easy to do.

A great tip I had from a rebuilder was to install the neoprene seal so that the seams do not line up with the block/cap joint. In other words the block/cap joint runs (like clock hands) from the 9 to the 3. If you tilt the seal to the 10 to 4 position you are adding more security against leaking. its easy to do.