Board index Flathead Power-Technical Questions, Answers, and Suggestions Big Twin Flatties main bearing case races

main bearing case races

Post Wed Jul 17, 2013 7:05 am

Posts: 309
Location: Cranbrook B.C. Canada
I just picked up a 1939 ULH basket case . The motor has good condition matching number cases.
I will be lapping main brg. case races , To do this , do I cut out the lugs and replace the races with 40 and later races? Or, could I just set up on a mill and cut the lugs just below the race surface and then lap races? I searched the archives ,and I don`t quite understand .
Thanks in advance.

Post Wed Jul 17, 2013 10:57 am

Posts: 543
Location: Wa, USA
If you use the 40 and later race, you can also drill the oil hole at the base of the V shape cast on the inside of the case just above the race.

Post Thu Jul 18, 2013 6:33 am

Posts: 391
The '40 left race has provision for the crank seal as part of it. If you machine out the end to line bore the early type you lose the ability to have either a bearing retainer and seal. Don't do it that way. Just convert to the '40 style and be done with it.

Post Thu Jul 18, 2013 8:23 am

Posts: 309
Location: Cranbrook B.C. Canada
Thanks for the input Woody & Rubone ,I`ll have to order my 40 & later main brg. races first and then I`ll get a better understanding.

Post Thu Jul 18, 2013 9:18 am

Posts: 1676
Location: Interlaken, NY USA

when I put my 37 cases into service last year, I machined a plate out of aluminum to cover the end of the bearing housing, machined a recess in it to accept the aftermarket lip type oil seal, and then screwed it to the bearing housing so I had modern oil seal on the mainshaft. There's room to do this if the plate is just thick enough to house the seal.
I'm running a belt, so I like to keep oil out of the primary.

Post Sat Jul 20, 2013 4:41 pm

Posts: 309
Location: Cranbrook B.C. Canada
That sounds like a cool fix Dr. D. ,Did you happen to take any pictures of your seal plate?

Post Sun Jul 21, 2013 5:46 am
don User avatar

Posts: 575
Location: Spokane WA USA
On the early cases 1937 1938 1939.
There is no oil screen or relief in the case to protect the scavanger pump.
(Oil fron the flywheel scraper galley)
If your cases are apart you might fit one.

Post Sun Jul 21, 2013 9:11 am

Posts: 641
Location: Wisconsin, USA
If you just machine off the outside of the insert on the left case and do not fabricate something like our crafty friend Dick did, the hole in the later race for oil feed will be partially exposed and crankcase pressure will push oil out. The best conversion is just to bore out the end of the inserts to the race hole size.

Post Sun Jul 21, 2013 10:06 pm

Posts: 309
Location: Cranbrook B.C. Canada
Yes, and thanks for all the ideas and tips on things that should be done. I want to check all my options and get it right.

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