Bearing problem: Stuck/Shifted bearing

My solution…


I had the same problem on my '07 KH29!
The bearings on almost all tapered interface hubs (square & ISIS) are designed to be press fitted on the axle. See: Interference fit - Wikipedia
As you may read in the link above the pres/interference-fit assembly relies on the friction between the connected parts (axle and bearing inner race).
So in production process mother parts (like inner race) are machined to a slightly smaller size and father parts are done slightly bigger.
In practice, however, because of production tolerances, a bad (or worst) scenario may happen if one uses a bearing with the inner race size located on the high side of manufacturing tolerance on a shaft sized in the low side of the allowed tolerance! This will obviously lead to poor press-fitting.
Coming back to our situation, its no wonder that the bearing slips if the friction is not big enough. This tends to happen more on bigger wheeled-unicycles because the higher frame flex induces higher side forces on the bearing!
I have all 3 KH unicycles (KH20, KH24 and KH29) all with Moment hub. I encountered this bearing slip problem on KH20 and KH29.

OK, now what to do?
First, I recommend AGAINST altering the axle or the bearing surface with any tool!!! This is NOT good!
Additionally I either don’t like the solution with spacers between the bearing and crank arm. This is suitable IMO only for NON-tapered spline designs (old KH, yellow QU-AX). I hope you immagine why…
Your best bet would be to find some Loctite or similar adhesive designed for this very problem (e.g. Loctite Bearing Mount 641…). These are low viscosity liquids that applied on the axle/shaft (before putting back the bearing) will increase dramatically the adherence of the press-fit!
Unfortunately they are hard to find and expensive!
I used with success Loctite 243. Although this is a medium strength thread locker it proved to cope well in the bearing application too!
get the bearings out, clean (degrease) everything, apply generously Loctite on both axle and inner race of the bearing, press them back quickly (use the part of the seat post of your KH that you may have cut out…) and leave overnight!

Hope this helps,

Loctite does make press-fit locking compounds which are better suited to this job than a thread-locker. I’ve used both the Loctite 609 (medium strength, likely to be removable) and the Loctite 648 (maximum strength, probably only removable by application of near-destructive 250C heat) and have found the Loctite 609 ideal for holding bearings on square-taper hubs. Loctite 609 is a lower viscosity than 641 and better suited to something which is already a press fit. Both are used with the Loctite 7649 primer. My local industrial supply house ordered them for me; expect to pay around $20 for the locking compound and another $20 for the primer.

Before assembling with 609, be sure that you have the spacer that sits between the bearing and hub in place. If you don’t, you’ll accidentally hammer the bearing on so far that you may not be able to grab the bearing with the puller arms to extract it. Be sure you have a good puller; it is required to remove bearings held on with 609!

I’ve done roughly 10-15 wheels with the same tube of 609 and have more than half left. Not a single case of a bearing pulling since I’ve started using it!

I think the problem lies in my flexy frame. I used too thin wall tubing. My next frame will be much stiffer and thicker.

If you’ve already taken the crank off and tried tapping the bearing back into place with a hammer (which i know is not a good idea…but it works if you’re careful) with no success, you may have to damage the bearing to get it off and buy some new ones.

Oh yeah the hammer and tube method worked fine, its just my frame is so flexible they keep working thier way out.

Oh, sorry I didn’t read the whole thread. Perhaps if you added spacers between the bearing and the crank they wouldn’t slide.

Yes but the crank cant tighten against the spacer, it needs to tighten onto the hub.