Loose crank

When I first started with this unicycle, the crank was giving me problems, but I was able to get it to stay tight by just tightening it as much as I could, and it hasn’t given me problems since, that was probably 4-5 months ago. It started to jiggle a little today, so I went and tightened it again, but as I rode away it instantly began jiggling again and gradually to a much greater degree than earlier today.

How can I fix this problem? I don’t have my own tools to tighten them, I have to go to a special place on campus that has the tools and it’s a lot of work.

i had something like this a while ago , i was recommended to stick some loctite thread lock around the nut and then tighten it up as much as you can , wait for 24 hours for it to set and everthing should be fine . it worked for me:)

Take it off, carfully clean all the mating surfaces, put the crank on straight, give it a very sharp tap with a soft mallet, tighten the nut (or bolt), then ride it for a minute or two and tighten it a bit more.

What do you mean a “very sharp tap”? Do you mean hard and fast, or quick but not very strong, or strong but with little surface area on the mallet?

A single clean strike using the natural swing of the mallet rather than the full might of your forearm, and “following through” rather than “pulling the punch”. Using the tool as it is designed to be used, rather than using it as a club to beat the crank into submission.

So I did that, and I thought it was okay. After a couple days of not messing with it, I rode for an hour without any problems. But today, two days after that, I noticed it start to wobble, and within minutes it got to the point where it actually fell off completely.

Did I not do a good job tightening it, or is there something wrong?

Your crank/hub interface is getting worn from you riding with a loose crank. Once it gets bad enough the only permanent solution would be to get a new crank(s).

You can get a good combination pedal/crank wrench for around $15, you can probably get a cheep one for… well cheeper.

Next time tighten it right away before it gets sloppy and you are less likely to wreck your cranks.

What did the parts look like after it fell off?

I assume you have the square taper hub-cranks setup. Does the corners look sharp, or are they rounded ? If you have rounded alum cranks, but the steel hub has good corners, new cranks should fix you. If they are both steel, and very rounded, you need a new hub as well as new cranks.

Buy some tools ! Life without tools means you aren’t learning how to wrench.

The thing that the crank attaches to is pretty sharp, the edges form two angles to make an octagonal figure that looks like a square. The crank itself is a little more rounded, but you can still see corners that would make it an octagon.

Interesting development:

When the crank fell out, I neglected to realize that the nut used to fasten the crank in would have fallen to the ground as well. I searched for it today to no avail, so I went to the circus and grabbed one of the spares lying around from the aged unicycles that don’t work anymore. The size of the hole was the same so it fit, but the circumference of the circle around it was bigger. It still fit, but was closer to the edges of the inside of the crank. I tightened it, and now it works fine. It doesn’t come loose at all.

But even if you remove the nut, the crank should stay in place, right? So if the only problem was the nut, why was my crank coming loose? Was it not able to tighten the crank fully somehow?

Only if you don’t ride the unicycle. The poor man’s way to get (square taper) cranks off without a crank puller is to take the nut/bolt off and then ride and hop around a bit. They’ll be loose in no time.

It’s possible the threads on your old nut were worn down and just not gripping anymore. Now if you give them a little tug with a crank wrench before each ride, you may never have a problem again. That’s what I do with my Cokers before road rides, for instance.

It appears there are two problems needing to be addressed.

  1. The crank arm to the spindle should be an interference fit, meaning they should force into each other at final torque setting. When the interference fit is compromised, it can be corrected with Loctite 660. I guarantee, when used correctly, Loctite 660 will correct a worn crank to spindle fitment.

  2. When a threaded assembly will not maintain torque, the usual cause is from initial torquing or over torquing and permanently stretching the thread lands. When a nut and bolt assembly is torqued, it is referring to the amount of stretch used to force the lands of the assembly together and it will permanently alter the distance within the threads per inch. Most nut and bolt assemblies are for single use and not to be used again after the assembly has been torqued and subsequently disassembled. Fortunately, in low torque applications when the male threads have been altered, you can use a Nylock nut to reliably hold the assembly together. Nylocks have a plastic ring molded into the outside edge and are for single use. Most hardware stores carry Nylock style nuts. To replace a standard nut with a nylock, take the old nut with you to the hardware store and have them measure the inside diameter and the threads per inch (TPI).

A crank bolt doesn’t really count as a low-torque application; the spec is for 25-35 foot-pounds. I wouldn’t expect that a Nylock bolt would help very much, especially if the crank has been deformed and is working against the bolt.

It should look like a 4 sided flat top pyramid, stretched out a bit. But only 4 sides, not at all octagonal.

If your hub really looks octagonal, there is nothing to be lost by banging the cranks on with loctite, and hoping for the best. Go easy on it, and shop for a new ISIS uni in the mean time. Assume a rounded, or octagonal hub will be much weaker than stock. So don’t push it .

It should be fairly easy to tell by looking (and slightly difficult to tell by reading ;D ) whether the “octagon-ness” you describe is mechanical wear/torque or the natural shape of the axle. Big square with tiny corners shaved off is fine, twisty square or corners dragged out of square: bad.

You might not be able to “eyeball” small problems, but you should usually be able to see severe ones.

Good luck,

John M