Board index Flathead Power-Technical Questions, Answers, and Suggestions Big Twin Flatties Changing from early to late case races?

Changing from early to late case races?

Moderators: Curt!, Pa

Post Fri Apr 20, 2007 6:19 am

Posts: 18
I don't know if this is right or not.

What I've been reading is that the early '38 cases can't be line honed like the later cases because of the plate on the edge of the bearing race.

If that is so, is there anything special that has to be done to install the '40-'48 case races in the earlier motors?

Post Fri Apr 20, 2007 9:26 pm

Posts: 1642
Location: Interlaken, NY USA

It always looked to me that that "plate" could be machined out and later races used. The plate is part of the cast in bearing housing. There was a special harley tool that was a flat round plate with 3 long prongs protruding that just fit the 3 holes in the plate and allowed pushing out the bearing race.
I was also told that the late right side flathead bearing race is different than the knuckle. the collar or flange that the thrust washer rides against isn't as thick. Does anyone know the truth of this?
Dr Dick

Post Sat Apr 21, 2007 1:10 am

Posts: 630
Location: belgium
Dick, they do have a different n°.
P.S. I think the knuck is the thinest...but please correct me iff I'm wrong!

Post Sat Apr 21, 2007 6:05 pm

Posts: 18
Is the OD of the early and late bearing races the same?

Post Sat Apr 21, 2007 11:13 pm

Posts: 630
Location: belgium

Post Mon Apr 23, 2007 4:45 am

Posts: 18
Has anyone tried machining the lip off, or does anyone know of someone that has done it?
Would the aftermarket '48-54 Panhead rubber case seal fit after the machining?

Post Mon Apr 23, 2007 12:50 pm

Posts: 150
Location: Carver, MN

While I cannot specificly remember doing this on flathead cases, I have updated early knuckle case more than a few times, and the procedure should be pretty much the same. From my notes:

Bore out "plates"on outside ends of the race bore in cases. (The more accurate job you do, the more support you will give for the new race.) Counter bore flywheel side of right crankcase half (pinion side) to 2.225" diameter, .135" deep to allow new pinion race to be pressed in to correct depth. (This counter bore is for the shoulder on the new race.) The sprocket shaft race will install "as is" once the outside plate is removed.

NOTE!!! These are my notes for a knuckle! The counter bore depth may need to be different for a flathead. You really need to take some accurate measurements of the inside width of your cases when they are bolted together, your flywheel width from thrust washer to thrust washer, etc to insure that the flywheels will be centered as original when you are all done. With all the variation I see in everything from crankpin width to shoulder thickness on aftermarket races, I don't think one can safely give firm figures without measuring each particular aplication.

Yes, then you can use the late style Colony sprocket shaft seal. Any good machinist shaould be able to do all this for you, and in my opinion is well worth the effort in order to "line lap" the races.

Post Tue Apr 24, 2007 3:50 am

Posts: 18

Thanks for your information. I think that I can adapt your Knuckle info to my Flathead.

Posts: 20
Location: Honolulu, HI., USA
I'm curious. Has anyone actually done this with a flathead (1937-1939)? The Palmer book mentions that the case races cannot be line-lapped ujless the case is modified to accept the later races. How is this actually done?m

Posts: 54
I have. Easily done, works fine.

Posts: 636
Location: Wisconsin, USA
Bone Digger, The cases are set up individualy in a milling machine, the race holes are indicated to center and the blind hole part of the cast insert is opened up. It's handy to start with a 1 3/8" drill bit to save boring time. The closed end part of the insert is generally much harder than the rest of the insert bore, so a sharp carbide bit is best. You may have to bore past the right race hole into the case a bit for clearance. It is also a good idea to drill the oil hole for the new style left case race while your at it. You will need some additional parts to use the late races. Once done you can accurately size your races for a perfect fit and you can use a Colony shaft seal to keep the oil in on the sprocket shaft side. A good thing, especially if you are running a belt.

Posts: 386
Would the aftermarket '48-54 Panhead rubber case seal fit after the machining?

Yes, as it fits into the race, not the case itself. So no issues fitting it.

Posts: 20
Location: Honolulu, HI., USA
Amklyde, thanks for the info.

Posts: 103
Location: Switzerland

It's a relatively easy modification if you have the right tools. I use a mill and a tool I do not know how you call in in english but you can see it on the pictures.
The right side you have to do from the inside because the case is in the way from the outside:
The left side can be done from the outside:
Result with the rubber seal in place:

Pa Site Admin

Posts: 5550
Location: Ohio USA

In USA laymans terms...the tool is known as an adjustable flycutter.

Posts: 3011
Location: Central Illinois, USA
It looks just like my "boring head".


Pa Site Admin

Posts: 5550
Location: Ohio USA

It is Cotten but boring head is not laymans terms. :wink:

Posts: 2677
Location: Los Angeles, CA
It can also be done in a lathe.

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