Crankcase Seal Fit

Post all your vintage karting messages here in the General Discussion Forum

Moderator: Rob Voska

Post Reply
Bill Hermsted
Posts: 88
Joined: Wed May 12, 2010 8:50 pm
Vintage Karting items owned: 3 AH58's and 1 MC45
User Agreement: Yes

Crankcase Seal Fit

Post by Bill Hermsted » Tue Jan 18, 2011 3:22 pm

I've seen some crankshafts that could stand to be ground down .010 or so to clean up where the seal rides.Most of these seals seem to be .040 under journal dia. on their i.d. Would the seal still do its job with a .030 fit?
bill

Rob Voska
Posts: 1704
Joined: Fri Jun 15, 2007 9:04 am

Re: Crankcase Seal Fit

Post by Rob Voska » Tue Jan 18, 2011 8:38 pm

Grinding a crank like that is tricky. Takes a very rigid setup so you end up round. Seals will adapt some & it might only take a few thousandths to clean one up. If you get to small you will end up with an air leak. A seal works both ways to keep air out & crankcase pressure in.

User avatar
Scott Kneisel
Posts: 477
Joined: Mon Mar 24, 2008 7:48 pm
Vintage Karting items owned: '63 Rupp Grand Prix, 66 Rupp Chappy, Mc6's, Mc8, Mc10's, Mc20's
Lotsa' other Macs
User Agreement: Yes
Location: Farmington, NY

Re: Crankcase Seal Fit

Post by Scott Kneisel » Tue Jan 18, 2011 10:55 pm

I have had real good luck with just polishing the seal surface with 600g emery. It cleans up most roughness. If the groove in the crank is too deep, I simply offset the seal when I install it so the lip is running in a different place on the crank. Never had a seal leak yet.
My 2 cents

Terry Bentley
Posts: 131
Joined: Wed Nov 10, 2010 3:21 am
Vintage Karting items owned: Kavalla Rupp Hornet Bug Margay Cates, Ala Kart
User Agreement: Yes
Location: East of DFW

Re: Crankcase Seal Fit

Post by Terry Bentley » Thu Jan 20, 2011 1:15 pm

It does depend of motor in question and which side needs repair. I can assume its a Mac, Westbend, or Clinton on PTO side.

Just for reference: The replacement seal for Mac motors on flywheel side is 6763. The dimensions from SKF show that seal is for a .688" diameter shaft. But the crank measures .669". The Mc 10 seal 102940 interchange to National is 481073 and is 6556 in SKF. Dimensions for this seal is for .656" shaft, but crank is still the same .669". I doubt you will encounter any problems with taking the crank slightly undersize, if you use a spring loaded seal correct for the original diameter or smaller. If you are using an universal OD grinder, it should be easy enough. If using a tool post grinder on a lathe, you may need to polish the surface a little after grinding.
One option is to polish the existing surface as best you can then use a double lip seal. You then fill grease between the double lips for additional insurance. Another option is to tape off and sandblast the surface thats is grooved and/or pitted, then fill with JB Weld. Sand down and polish to existing diameter and you are fixed up. Not 100%, but does get the job done. You wont have this option on a Power Products, due to the seal design.

These suggestions have been put to use in the past and worked. Your milage may vary.

Post Reply