I had a conversation with a fellow bolter at Townsend about the old "rope seal" oil leak problem that all of us seem to have. Chevy engines can be modified to use a full circle lip seal, which I've been doing for quite some time. GMCs, however, have a flywheel flange that's bigger than the oil seal surface, so that's not an option on those engines. I'm thinking about developing an adapter to make use of a 2 piece neoprene seal for a small block Chevy, or possibly some other engine by machining the crankshaft, and the engine block for an adapter to accommodate the newer style seal. Does anyone have a small block crankshaft handy to get a measurement of the rear seal surface diameter? I've got a 270 crank that's accessible for measuring, but I don't have access to a V8 crank without dismantling an engine right now. It might be possible to find a closer match for the crankshaft seal diameter, even if it's a Ford, MOPAR, or some other make of engine. Thanks! 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!
Jerry - A quick scan through some Chevy books shows the following general details about the rear main journal diameter:
The large journal cranks have 2.650" mains. These were in the 400 cubic inch small blocks only. * The medium journal cranks have 2.450" mains. These were in the small blocks starting in the 1968 and later model years. (1968 Chevy Truck Overhaul Manual says = 2.4479" - 2.4488") The small journal cranks have 2.300" mains. These were in the small blocks built before 1955-67. *
* Granddaughter showed up for the day so I didn't have time to check actual books for details like found for the '68 and later cranks.
Hope this helps.
~ Dan 1951 Chevy 3 window 3100 Follow this story in the DITY Gallery "My Grandpa Carl's Truck and How it Became Mine" 1966 Chevelle (Wife's Hot Rod) | 2013 Chevy Silverado (Current daily driver) US Army MSG Retired (1977-1998) | Com Fac Maint Lead Tech Retired (1998-2021)
That would be a good scheme, Jerry. As you know (and as we've discussed here) GMC engines have a leg up in that they have an oil slinger and a wee notch machined (to catch enough oil to lubricate the rear main seal). You'll remember I suggested using the Speedi-Sleeve on the 235 or 261 and leaving the lip in place to act as a slinger to slow the flow of oil and deflect it around the machined recessed area there. GMC image provided by Bill Hanlon.
~ Jon 1952 1/2 ton with 1959 235 | T5 with 3.07 rear end
Dan, that's good information- - - -which I've had in my shop specification manuals for over 40 years. I'm looking for the diameter of the OIL SEAL area of the small block V8 crankshaft- - - - -where the 2 piece rear main seal rides. I just don't have a small block V8 crankshaft handy to measure right now without tearing down an engine!
Edit:- - - - -got the dimension from my friendly local engine machinist- - - - -2.431 inches. Now I need to measure a GMC seal surface to see how close that size is. I can use a tool post grinder in a conventional lathe to size the crankshaft, and make an aluminum carrier for the seal to fit the engine block. 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!
Jerry, we are waiting to see if the Best Seal, shimmed and pinned on both sides and packed properly works. The crank was also knurled in the proper direction then polished. Just waiting to get back on my feet to complete the install. (302 GMC)
I'm hoping for the best in your situation. I believe I can come up with a permanent fix, using a 2 piece lip seal from a different engine. It will probably take some machining to both the crankshaft and the block, but it should be a "one and done" fix. 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!
