First, what size bearings should I order to fit the Yuni/Nimbus frame?
I decided to give my unicycle a going over, cleaning all the MUni goop and grime from all the parts. While I was cleaning I noticed that one of the bearings moves slow and smooth when spun as though it’s well greased, while the other bearing spins quite a bit but makes some noise and feels as though it has been depleted of grease. Does this mean it needs to be replaced, and is it hard to remove the cranks and replace the bearings?
I haven’t worked with bearings yet, but I had the metal disc cover fall out of the bearing once when I took the tire out. It exposed the bearings and I would have been able to grease them up at that point, but elected to put the bearing cover back in and clean it later. Give it a gentle prod and see what happens.
I don’t know if you have access to the plastic or rubber covered bearings.
A bearing which turns easily and quietly but won’t spin is OK. The grease slows them down pretty quickly. A bearing which spins and makes noise is dry. It may just need to have grease pushed into it. Use a sharp instrument to carefully pry off the bearing seal. Stuff or squeeze grease into it. Pop the seal back on. If it remains dry it will have a short, unhappy life.
If you decide to replace them, most bearings on unicycles these days are 40mmx17mm. They are in the 6203 series. If it is not too worn, somewhere, probably on the seal, it will have a number like 6203 or 203. They are available in a huge variety. Something with low tolerance (low grade) with plastic seals on both sides is adequate. You can get them from a local bearing distributor but be prepared to answer all kinds of questions about the specs. Here in Seattle they can be had for 8 bucks each. In Alaska it might be different. You can order 6203 series bearings from unicycle.com.
You will need a crank puller that you can buy at a local bike shop. You will need a bearing puller you can buy at an automotive store, bike shop, or hardware store. Both of these tools may also be purchased from unicycle.com.
To press a bearing you will need, at minimum, a tube or pipe with ID larger than the diameter of the axle but smaller than the OD of the inner race of the bearing. You can tap the bearing on with a mallet striking the pipe and driving the bearing onto the axle. Back the other side of the axle with a piece of hardwood to prevent damage. A hand press with the pipe as a guide is a much nicer solution but not as readily available.
More complete instructions may be found for each step by searching past threads. There are probably some extensive replies to similar questions about cranks, bearings, tools, etc. Some of them have links to catalogs that will show you what these tools look like.
> To press a bearing you will need, at minimum, a tube or pipe with ID
> larger than the diameter of the axle but smaller than the OD of the
> inner race of the bearing. You can tap the bearing on with a mallet
> striking the pipe and driving the bearing onto the axle. Back the other
> side of the axle with a piece of hardwood to prevent damage. A hand
> press with the pipe as a guide is a much nicer solution but not as
> readily available.
Is this how the pros do it? Banging on the end of a piece a pipe to seat
the bearings. How much resistance can I expect? Can I use a piece of
regular old pvc or will it require some real hardware?
I have tried using PVC and it didn’t work very well. It’s not quite strong enough. You may be able to press one bearing on with the PVC but it will not hold up for a second bearing. Metal pipe or conduit works better.
Loctite sleeve retainer is also good to hold the bearing on the axle. The bearings are held in place by a press fit and sometimes that press fit gets loose. The Loctite will fix a bad press fit and keep the bearing from slipping on the axle during use. Don’t worry if the Loctite says it’s high strength. Pulling off a Loctited bearing is no more difficult than pulling off a non-Loctited bearing.