I’m seeking advice about a loose crank. The unicycle is the 29" Nimbus with square-taper hub. The crank is held in place by a screw (plug? cap?) that is tightened with an allen key (wrench).
For some reason the right crank keeps working loose. Should I be using some sort of loctite, or should I just tighten it with more force? How much force should be used with the allen key? I am sure I could apply more force but I’m already approaching the point at which I feel the allen key would bend, or round itself in the socket. What can be done with this situation?
It might be because the inside of the hub theard is stripped or the bolt is stripped. i wouldnt reconmend using force to bolt it in. that will make it worse.
It might be an idea to replace the bolts. tho
but thats just me
If you have ridden your cranks while loose it is highly possible that you have flared the square taper on your crank so it no longer matches the spindle. If you look at it where it engages the spindle you should see that the flats are… flat. If they are rounded, or not flat, even the littlest bit, they won’t tighten correctly.
Generally it is recommended to put a little grease on the spindle flats, not loctite. Loctite on the threads will help prevent corrosion and maybe prevent the bolt from becoming loose, but it won’t fix the problem if your square taper is not right. In this case you will need a new crank arm.
So I would try the loctite first and see if that solves the problem. Don’t use the red or green loctite, use the blue. If it doesn’t work a new crank arm should solve it.
Hammer it on good with a rubber mallet, then tighten it up. Ride it a couple hundred feet then tighten it again. Ride some more then tighten it again. After repeated tightenings, you will find that the crank has finally set, unless the crank has already rounded out.
As soon as I can escape the crazy work schedules I will remove both cranks and check for flatness of the spindle flats before trying the other advice.
Thanks, guys, for the tips.
Update: finally found time to address that loose crank. Visual inspection did not reveal any loss of flatness in the crank-to-square taper bearing surfaces. I’m not sure that means anything, as I expect any wear there might be hard or impossible to detect visually. (can any of the mechanics here confirm or dispel that notion?)
I tried the hammer-it-on-tight advice using a rubber mallet. Then I went to tightening the bolt that holds it in place. I found that I was able to go seemingly forever making it ever so slightly more tight by settling my 220 pound body weight on the end of the allen key, (making the end of it move a quarter to half inch each time). I worried that this forever tightening meant the threads were stripping, but I noticed that the allen key, (I believe 8mm in size), slid easily into the space between this crank and the bearing cap, while on the other crank it would not fit into that space. I took this as indication that the right crank had some distance to go before being fully seated, so I kept on keepin on.
Eventually, after a few dozen repetitions of this scary incremental tightening, I got it to the point where the gap between crank and bearing cap was about equal to the other side, as determined by the allen key no longer fitting into that gap. This gap is now just less than 8mm wide on both ends of the axle.
I haven’t tried riding it yet, I have to go to sleep now in order to start a 1am work shift. [edit: reviewing the responses I see I skipped the step of riding/tightening/riding/tightening…ooops, I guess that will have to be done later]
Someone in this thread advised using grease on the square taper; I wonder if this scary tightening procedure would have been easier and more sensible had I done that. (I had no grease handy so I did the procedure “dry”).
That’s it, I won’t know until I ride it if I solved the problem, but I have high hopes that I have. As usual, if I’ve done anything wrong or raised an important issue regarding crank maintenance I hope someone will pipe up. Thanks again for reading!
You should definitely grease the tapers; it will make installation easier, and help the crank to go on straighter and be less likely to loosen.