QuestionWhat is the easiest way to replace a rear main seal on a '66 401 buick and should a rope seal be used or upgrade to a neoprene.
AnswerI don't know of any easy way to do this. To get a really good job, you need to remove the engine and turn it over in an engine stand, remove the pan and crankshaft so you can see what you are doing. Then clean everything to spotless brand new condition, and then follow the procedure given in your shop manual, or if the shop manual only discusses installing the rope seal, use the instructions that come with the neoprene seal, which is certainly a better seal.
Assuming you want to avoid all that work and do it the quick and dirty way, the only method that I can recommend is to jack the car up high, USE SAFETY STANDS, drop the pan, remove the rear main bearing cap and loosen all the other main bearing bolts a couple of turns, then work the old seal out of the groove in the block any way you can.
The further you drop the crank, the easier it gets, but you will be limitted by the slop in the front seal of the transmission- you don't want to stress that much because you will cause a much worse leak of transmission fluid if you do.
Make sure everything is as clean as you can get it, using "pipe cleaners", Q-tips and anything else you can devise to get all the glop out of the groove. Do the same in the main bearing cap. Then with a very thin coat of Permatex "Ultra-Copper" on the outer part of the seal, slide each half into place in its groove and put it all back together, making very sure the rear main bearing cap is touching only clean bright bare metal everywhere.
While you have the pan down, snake a screwdriver tip or your pinky up around the crank gear and wiggle the timing chain to see how much looseness you can see - if it's loose, you're in for a major overhaul soon anyway.
Depending on how much the leak bothers you, you should consider waiting until you are ready to rebuild the engine - then do the whole job right. Oil is pretty cheap by comparison, and a fresh sheet of cardboard on the garage floor every month is not a big price to pay!
Before you launch into this whole project, make VERY SURE that the leak actually is the rear main - very frequently with these engines, the rear main gets the blame for a leak that actually starts up at the top of the engine, and runs down around the back of the engine to drip off under the rear main. Culprits can be valve cover gaskets, valley cover gaskets, or oil senders - so check very carefully behind the intake manifold, and if you see oil back there, I'm guessing your leak is up there somewhere.
Dick
