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Clearance between DS case and bearing sleeve?

billirwinnz

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VOC Member
My TTR crankcases have been cracked and welded at some point in their racing life and I've just discovered that the crankcase hole for the bearing sleeve is out of round. I plan to have it line bored a minimal amount larger and make a new bearing sleeve to fit. Calculating the difference in thermal expansion between a 3" sleeve in alloy I get 0.0035" growth in the clearance over 110 degrees celsius. Can anyone tell me what the standard cold (say 20c) interference fit was? That much interference cold will lock up the CN bearings or should they be C3?

Bill
 

greg brillus

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VOC Member
I would say the sleeve should be a good interference fit in the crank case housing, but not necessarily the bearings themselves given you are putting a steel bearing into a steel sleeve. Even one thou interference will cause the bearing to broach it's way in.......On post war cases we sleeve the housings with steel sleeves with about 0.003" interference, but the actual bore of the sleeve gives about not more than 3 tenths of a thou for the bearings themselves...........Others might prove me wrong, but we have done many engines like this with no failures so far..........remember too that the large diameter Thackery spring washer for the outer ball race is to allow for movement of the outer bearing and the expanding cases once the engine heats up in service.
 

billirwinnz

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VOC Member
Thanks Greg
Makes sense to me. Sorry I didn't see this until now as I had been expecting email notifications of any replies.
Cheers Bill
 

genedn

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VOC Member
You could do what danny smith has been doing for years and hard chrome the bearing race over size and then grind to fit the new ID of the case once lie bored. Just an idea.
 

billirwinnz

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VOC Member
Thanks. I was lucky. The old crankcase repair had shrunk the case and we were able to line bore it back to standard dimensions. The bike is on the road and running beautifully. Noticeably smoother than before with less than .001" of flywheel runout and both bearings in line. I could find only standard rollers rather than C3 so the bearing is just tight when the sleeve is pressed into the case but from my calculations warming of the alloy versus the steel sleeve theres no nip at normal running temperatures. Velos have a .004" nip on their taper rollers when cold and it doesn't seem to trouble them.
 

Robert Watson

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On tapers the "nip" is measured by how much further the cone is pushed into the cup, not the radial clearance, and that is for two tapered rollers back to back, or face to face, so like comparing the weight of one fish and the length of another.........

the drive side on the Woolly has tapers, face to face With the cups back to back in a steel sleeve and with the clearance/interference held by a spacer between the cones, Grind the spacer to suit, I'd have to look it up but .005 crush seems to ring a bell.

Also, after the straight roller outer races are put in, if not C3 then the inside of the outer can be lapped in place to give a couple of 10'ths extra clearance.
 

billirwinnz

Well Known and Active Website User
VOC Member
Hi Robert
I agree about the fish but my point was that slight initial tightness is soon overcome by thermal expansion. The relative expansion between the steel and alloy diameters will be about 0.001" between 15 and 70c.
I'm not going to pull the motor down again as it's running so sweetly.
Cheers Bill
 

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