The Stovebolt Site Forums The Shop Area Engine Shop Rear main seal

Hi Everyone, I decided to attempt replacing my seal on my 248 GMC because it leaks all over the place. I have removed the oil pan and now have several questions. I tried loosening the nuts on the bearing caps and found them to very tight. I'm going to need a bigger wrench. Is there a danger of snapping a bolt? Also the instructions I've found here say to remove the oil pump, Is that necessary? Thanks for any suggestions.

Yeah..the rear main bolts are very tight. I just pulled the engine out of my 78' and replaced the seal, along with some other parts. Those bolts are tightened from the factory to about 60-80 ft/lbs. Take a pretty good size ratchet(3/4 drive) and then get a tube and slide if over the ratchet for more leverage.....or you can use an air wrench, but not everyone has those. You shouldnt have to worry about twisting off a bolt head, the bolts are fine thread and are made for that kind of pressure. Its a lot easier to get at the bolts with your oil pump off. That might be why they tell you to take if off.

Have fun working on it , hope this helps and let us know how it went.

Thanks for the reply. I was able to get the bolts out with a larger ratchet, but I wasn't able to drop the crankshaft at all, it didn't even budge. I wonder if there is a difference between the 248 GMC engine and the Chevy engines?

you still have the other bearing caps holding on the crank, unless you took all of them off...but even when you take those off the crank will still probably be hard to budge from the seal from the pistons.

Dustin