Bearing Spacing HELP!!!

Building up an old unicycle for a friend of mine who needs one…I believe the specs state that the frame is machiened for a 40 OD bearing…can you shim UP? I have a wheelset that i was thinking about putting on it that has a 42 OD bearing on it… Just wondering…does anyone know if you can change it to a 42 by going to a shop and having them machiene it out for me?


can’t you just try it?
as long as it isn’t a perfect fit with the 40mm bearings you should be good. my guess is that it isn’t, there are quite a few things you can do to mess w/ it as well.

I believe the OP wants to put 42mm bearings in a frame designed for 40mm bearings.

Short answer: no. You can’t shim up.

You could just go ahead and put the bearings in the frame and clamp 'em down but I believe you’d trash your bearings in little time.

What you should ask is, how valuable is that frame? Re-machining the holders to accomodate a larger bearing might cost you more time and money than a new frame. It might also rob the frame of some of its strength… dunno unless you told us what kind of frame it is. is selling Nimbus / Yuni frames for around $40 right now. If your friend can cough up the cash, he’d be getting a sweet deal.

wait could i put some 40mm bearings on my existing hub…its an old kh moment hub…is that possible…?


I agree with Maestro8 You will probably bust or ruin the bearings pretty quickly by tightening things down. There are bearing houses or supply companies that probably have a bearing that will fit both OD and ID outside diameter and inside diameter and have the proper width. SKF is a really good brand but may be more expensive than you want spend. If you live in a realatively large city you might even be able to take the uni and wheel to the bearing supply and they might be able to figure out what bearing you needed and even mount it for you.

Line boring the caps will probably cost a bit of money but if there is a machine shop (good one) around you might take it to them and get a quote. They might not have any jobs pending and that coudl work in your favor.

IF you do it your self your going to need a caliper that reads to the nearest Thousanth .001" (english) or some fraction of mm. I’m 52 and use english measurments in my shop (yea yea I know blah blah blah). I’ve replaced bearings on my unicycles using SKF so it’s possible. Good luck.

Remember if it isn’t grown it has to be mined.