Making the bearing cap bolts good and tight.

I had been accustom to snugging up the bearing cap bolts on my unicycles, that is until I bought a KH 29" frame.

KH does it right. The bolts on the KH frame tighten up, holding the bearing cap to the frame without compressing the bearings. KH has machined holders to sized to hold the bearings, where on my other unicycles, they crudely clamp down and squeeze the bearings. The squeezing makes it possible to damage, or wear out the bearing faster. Also since those bearing screws can not be tightened, they then to become loose.

So when I was out riding my Nimbus 36 and my wheel felt squirrelly, then found the bearing clamp bolts were loose, I wished they were more like the KH holders.

(One thing to be noted is that I don’t like locktight, I take things apart often enough that I don’t want to deal with that stuff.)

So for my Nimbus 36, I found a combination of washers that fill the gap between the frame and the holder cap. This way I could tighten the bearing holders tight without compressing the bearings. Actually the washers were just very slightly too thick. So then I took a one inch slice of a inner-tube and stretched it around the bearings, to increase the bearing diameter size. Then bolted it together, tightly!

Now, with the bolts tight the wheel turns freely, and bearing are secure. I hope those bearing bolts will tend to stay tightened now that they tight, and not just snug.

I think this is an improvement. Of course it would be nice if future unicycle designs were like the KH frame. Any comments are welcome.

Pictures below; The blurry one attempts to show the washers added between the frame and bearing cap. The other shows the piece of inner-tube, a bearing, and the result of stretching the tube piece over the bearing.

I thought about this one time when I was trying to get bearing caps on right but never did anything with it. Glad to hear it works. I have gotten better at adjusting bearing cap tightness but I may still give the washer idea a try.

Yeah, I thought about it… Thinking where or how to get perfect spacers, how to measure for perfect tolerances. Then decided, what the heck, I’ll just go experiment with what I have. It worked out. :slight_smile:

Hmmm I noticed the problem too, as well as de-threading several bolts. About to rebuild my uni with new bearings and caps so I’ll have to give this idea a go, maybe with old parts first to make sure it works.

Have you tested the idea on long rides and some trials ect?

I’ve gone 10 miles and they stayed tight.

But now I’ve made them bulletproof, probably over done it, but I need not ever worry about them loosening, ever.

Adding to what I posted earlier, I replace the cap bolts with longer bolts (M6 x1 inch) , washer and lock nuts (nylon insert locking). So now I tighten the cap bolts, then tighten the lock nut. The lock nut keep things tight. If you do this always put on/tighten the lock nuts last and remove the lock nuts before unscrewing the bolt.

So here is the latest picture with the longer bolt, washers, rubber, and lock nuts.

Nimbus Frame

I always wondered why UDC said the bearing housings on the Nimbus 36 were machined. The ones on my frame are sure not machined.

how can you tell if bearing holders are machined or non-machined? :thinking:

Over tighting bearing clamps can do worse then you might think.

When I first got my new Torker DX a few years ago, I way overtightened the clamps, and within two weeks split the actual bearing casing all the way around on both sides.

Big bummer.


Didn’t you ever spin the wheel?

If mine are even slightly too tight, the wheel bogs down really fast when you spin it.

Kris Holm unicycles and the Nimbus 36 (like the above photos) have machined caps. Other low end unicycle have stamped caps. KH has better machined the caps to capture the bearing without squeezing.

I’m sure it comes down to a cost trade off decision. I don’t mean to criticize the Nimbus 36 frame, it’s great, and at $120, as great a value. The KH frame is one of the best made frames, and cost $199 because of the extra work involved.

Nice. Think I’ll give the inner tube and washers a go when I rebuild my uni with new bearings. Wont go as far as you though, I go easy on my uni. :stuck_out_tongue:

I don’t see what your infatuation with torque is going to buy you… there are many ways to keep a nut on a bolt without having to resort to cranking on a wrench.

As many have noted, over-tightening bearing holders is a bad thing. Also, loose bearing holders can cause problems down the road. Without careful measurement, this washer method may result in either of these two situations.

As you have discovered, nylock nuts do a great job to stay on the bolt. Others have discovered solutions such as Loctite to keep their nuts in place.

I’ve replaced my bearing holder hardware with slightly longer Grade 5 bolts and nylock nuts and have never had to touch the hardware post installation.

It isn’t rocket science, figuring out how much to tighten the caps… why dumb it down even more?

Edit: added links.

Hello maestro8, Yeah, I have over done it. Perhaps I took the wrong tact when I first tried to duplicate the type of solid fit that the KH has, or my stubbornness to not use lock-tight. I agree that a locknut is a reasonable solution. Things just progressed this way.

The extended bolt and locknut without the washers between the cap is fine. Allows the bolt to be snugged up to securely hold the bearing, then the locknut used to keep the bolt from backing off.

Great feedback.

Have since taken the wheel off. Found that with the bearing wrapped with rubber, the caps are hard to remove from the bearings. Used a rubber hammer to knock them off. Also the rubber added to the bearing gets compresses so that reusing is not practical. All and all the spacers and inner tube wrap does not really work that well. Good thing it turned out unnecessary.

So when I put things together again, I skipped the inner tube around the bearings, and the washers between the cap and frame.

Did use the longer bolts with the lock nuts. That does work fine.

on a similar clamp up fitting on a car exhaust i use two nuts on one bolt: tighten the clamp until it feels right, then put another nut on top, hold the first nut still and then tighten the second down on top of it.

also, for those that dont like locktight or have bother with it, most locktight turns to a liquid/jelly when you warm it up with a hairdryer or an electric paint stripper gun to about 100 degrees C or so.

nice solution through with the washers and the rubber. remember you can make basic shim washers with a file (by putting the washer half in a vice,filing then turning it over to file the side that was just inside the vice) if you really need to/your working on the dark side of the moon.

I have had the same problem, I think I will use the longer bolts and extra nut, I dont think that a nylock nut is really nessisary because it is not the only thing that is holding the bolt from turning and they are really only work 100% the first time, after that the nylon part gets deformed.

I think I will see if I can get the bolt the right length and use a dome nut.

Thanks for the great idea guys!


The nylock nut is not intended to keep the bolt from turning, it is used to keep itself from turning… so the nut will not become loose from vibration. In my experience, the nylock nut stays tighter, longer than a conventional nut with a locking washer.

The nylon insert inside the nylock nut is an elastic material; while it does deform, it retains much of its original shape after removal. It is quite useful after many applications, not just the first time.

If you’re really anti-nylock, another option is to use a pair of nuts on each bolt: one to lock the other in place. This, however, is more tedious to install or remove.

I am really not anti-nylock and believe that they are the best answer for someone who needs a nut to stay put if they can’t tighten it all the way but this is not the case with a bearing holder bolt coming out of the top. Just screw any nut down and it will effectively lock that bolt in place by putting opposite forces on the threads.

two nuts would be compleatly unnessisary as the upper bearing holder is threaded.

Whats the concencses ?

I have the problem with my 29". My bedford frame has a castle bolt that goes to the bearing caps. The Bearing caps are fastened by a lock washer and acorn nut. The acorn nut is always coming loose. I’m afraid to overtighten.

Want to remove the acorn nuts and put either locking nuts or something else.

Perhaps I’ll use the long bolts and two nuts or just try a self locking nut.

What works best ?

There’s really no reason to discount loctite. There’s 3 different grades to work with: The one that’s somewhat permanent that can be broken apart, the one that I use mostly when I’m assembling a motorcycle engine along with a lot of other mechanical stuff that is designed to hold but can be removed pretty easily, and one that wicks into an already assembled piece. Having that little tube in your tool kit takes up so little room and it’s really not that bad to put a drop on some threads as a matter of practice. Like always greasing the pins when you work on car brakes, or keeping the cells in a battery at the right level.