I'm starting to assemble my 270 GMC. My rear main seal is a graphite style, I believe from a Best Gasket set. It doesn't fit the groove very snug and the crush on it isn't much. By the time it flattens out to fit snug in the groove it may not be tall enough to make a good seal on the crank. My other 270 has the old braided style and its been in there for 30+ years and no leaks. Should I try and find the old style braided type??? Where? Thanks!!!! Jay D.
Last edited by Gdads51; 05/14/20261:13 PM. Reason: add detail to title
Try using the stainless steel retaining strip from a discarded windshield wiper blade as a shim between the rope seal and the block and main bearing cap as a spacer. I've repaired several chronic leaky rope seals that way. If you have the engine out of the vehicle on a stand, stick the spacer into the bottom of the groove with some high temperature epoxy. Jerry
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt! There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway Love your enemies and drive 'em nuts!
We went through this on my 302. We tried pressing in a thicker "Best Seal" with .010 shim on both sides and pinning the seal. We knurled the crank, (in the right direction) polished it and you could tell it was tighter on the crank. Well, it leaked again.
We are going to try again with a thicker shim because the timing gear failed and we need to disassemble the engine ....AGAIN!
yep, i don't think this one going to seal just to small to fill the gap i'm going to try and find the old-style rope one. thats what i used in my other 270, fitted the rope seal in the groove and forced it in tight with a piece of pipe then trimmed it. Jay D.
Holy Mackeral! The intake system is bigger than the engine!
1950 Chevrolet 3100 (Ol' Roy)
1939 Packard Standard Eight Coupe (The Phantom) | 1956 Cadillac Coupe de Ville (The Bismarck) | 1964 Ford Galaxie 500 coupe |1966 Ford Mustang (Little Red) | 1969 Pontiac GTO (The Dishpit) I 1979 Ford F-100 | 1976 Ford F-150 (Big Red) | 1995 Ford F-150 (Newt)
I'm working on an idea to grind the seal surface on a GMC crankshaft to a smaller diameter to accommodate a 2 piece lip seal (maybe for a big block V8?) and fabricating an adapter to fit the rope seal groove in the block and rear main bearing cap. Eliminate the rope seal altogether! Jerry
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt! There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway Love your enemies and drive 'em nuts!
I wonder if there's a way to machine a round recess in the back of the block and install a modern day one piece seal into it.
Doable on a Chevy engine, but the GMC flywheel flange is larger diameter than the rear bearing journal from what I've seen here. It would be tough to install a one piece seal, unless you get one that's stretchable. LOL! Here's a pic of the modification on a 216.
Kevin 1951 Chevy 3100 work truck Follow this saga in Project Journal Photos 1929 Ford pickup restored from the ground up. | 1929 Ford Special Coupe (First car) Busting rust since the mid-60's If you're smart enough to take it apart, you darn well better be smart enough to put it back together.
