crooked crank arms?

[codongolev]

look, I'm probably just an idiot and that's why I don't know about these things. but please bear with me, I'm trying to learn.

I was riding my unicycle today and my foot somehow managed to slip off the pedal. I rode one-footed inadvertently (which was kind of cool, I've never done it before) for about one rotation, then fell off. when I picked up my unicycle, the one crank was off by about 10 degrees from where it should have been (so that the pedals were no longer straight across, but bent a bit). I tried searching for a fix, but I couldn't find one, and I also am having trouble finding any diagrams of how unicycle cranks attach. (if anyone cares, I have a sun 26", pretty much the same as it came from the factory except with new pedals.) so I decided (probably unwisely) that, if it was banged into that position, banging it back would probably not hurt anything more than it already had been hurt. so I used a rubber mallet and slammed it back, and it's in fine working order now (I bounced a bit on it and there was no movement). I'm just wondering if it's still safe to ride, and what the correct way to fix it would have been. I'm thinking that something with the attachment mechanism was bent, and I just bent it back.

[HYDR8]

Hmmm, I would suggest getting a new hub, just in case. I have a Sun 20in. and it had a terribly twisted hub. At first I thought it was my crank, but it was part of my hub, so that might be your problem, is a twisted hub. I think it was just bunnyhopping off of a curb that bent it for me. You might have solved the problem by banging it back into place, but I'd get a new hub/crank for it, just in case.

Hope this helped

[codongolev]

thanks. I'm a little short on cash, and my LBS doesn't have much in the way of unicycles, but I'll try to find a new hub when I've got the money. (I really ought to research the bike shops in my area. there might be a unicycle goldmine I don't know about.)

[tholub]

It sounds like you bent something. It could be the hub or the crank. If it's the hub, you're probably looking at something that will fail soon. If it's the crank, and if the crank is steel, it might last being bent, although it will be more prone to bending again.

It's also possible that your crank is not bent, but loose; make sure the crank bolt is very tight. If it's not, you will likely bend the crank (or at least the crank tapers) very quickly if you continue to ride it.

[ThisIsAUsername]

Originally Posted by HYDR8

Hmmm, I would suggest getting a new hub, just in case. I have a Sun 20in. and it had a terribly twisted hub. At first I thought it was my crank, but it was part of my hub, so that might be your problem, is a twisted hub. I think it was just bunnyhopping off of a curb that bent it for me.

yes, the same happened to my sun, a very cheap unicycle. so i also believe a twisted hub is the case.

trying to fix the hub or bending it back into place is not a good idea as it will probably cause further damage.

[codongolev]

thanks for the input. I'll try to see if I can replace the hub sometime soon, if I can. otherwise I guess I'll ride until failure, it was only $75.

[Doug]

If the crank was bent or the axle twisted and it was steel then it may have become stiffer by the bending and reversal. Think of a clothes hanger wire. It gets cold worked with each bending. It may be better than the original.

[tholub]

Originally Posted by Doug

If the crank was bent or the axle twisted and it was steel then it may have become stiffer by the bending and reversal. Think of a clothes hanger wire. It gets cold worked with each bending. It may be better than the original.

I'm pretty sure if you bend a clothes hanger back and forth, it will eventually break. It is not likely that a twisted axle is being made stronger in any meaningful way.

[Doug]

Yes, multiple reversals of the wire will cause it to break. Cold working of a steel will move the yield point higher but do little to the ultimate tensile strength. Cold working will make whatever component bent stiffer by increasing the yield point. A stiffer material will not distribute an applied load as well as a soft one. The resulting point load can achieve the ultimate tensile stress with less deflection. Anyway, it's been more than 30 years since I've had metallurgy. I'm bound to have forgotten something.
It will be interesting to see what actually fails or just becomes more loose to the point of affecting the ride.

[codongolev]

I've forged small knives out of nails before, so I know what you mean by becoming cold forged. and also, the whole thing about clothes hanger breaking; I use that method all the time to break clothes hanger, and I know for a fact that it's harder to bend the second and third times because it gets hardened. also, a hub is quite a bit bigger than a clothes hanger. I'm probably just being optimistic now, though. however, if anyone wants to know, I took it to a friend's party and did some heavy riding on it (down the hill in his backyard, through his backyard, over the curb, etc) and did some bunny hops, and the pedals didn't move at all. it did start having a funny click-like feel in the left pedal about halfway through, but that went away after awhile. (on a completely unrelated note, he happens to also ride and has a 24" in his garage. I rode it in his backyard some, and it was really hard to get used to the smaller size. the seat was also really low (I'm 6'4"), so I had to either pull my legs up really far or float and hold the seat. but it was really fun.)

[codongolev]

hey, just a quick update. I was riding my unicycle around yesterday, and all of a sudden I felt my crank go loose all of a sudden. so I tightened the bolt and I was good to go. the only reason I say this is because it might have something to do with the twisting; the nut was literally not tight at all (I thought the socket was too big at first because it spun so freely), so I figured it must have been that way for a while and the crank just now popped off.

[Hung Like Saddam]

It could be if the nut was loose that the crank had moved to the end of the taper and had twisted on the loose fit. If this is the case, hopefully the crank taper is not too damaged and tightening the nut should fix it. If not, the crank is more likely to be damaged than the hub.

[tobbogonist]

Originally Posted by codongolev

I use that method all the time to break clothes hanger,

To what end sir?

secondly, talk to your lbs, they generally have connections that sell unicycle products even if they have nothing in store.

[codongolev]

the saga has ended, as I have found the source of the twisting. however, I unearthed a different problem.

I found that the nut holding the crank arm (the one that turned) kept coming loose, and the crank arm in turn. I took it all apart (I don't have a crank puller, but as it was already loose I could just wiggle it) and found a stripped-looking crank taper. this is obviously the source of the problem; you can see the marks from where the crank arm scraped against the taper edges and rounded them down (I figure when it popped of the tapered part, the smaller end of the taper allowed just enough wiggle room to strip the corners). so what I did was I took a file and filed the taper's sides just a bit to allow the crank to seat farther down the taper, as well as to square up the taper as much as I could. I then pounded it in place with a rubber mallet to make sure it was as seated as possible, then I reattached the nut using some medium strength threadlock (I would've used a torque wrench, but the adapter to fit smaller sockets on the head was broken, so I just tightened it to the point where I felt it was secure but not too tight. I've lurked long enough to know that overtightening kills unicycles).

here's to hoping I don't have any more problems after this. (these are all temporary fixes anyway; I only plan on this uni lasting me until I can get enough money together to buy a new or barely used one. this one is a $75 one from craigslist.)

[tholub]

Good luck with that, but I'm afraid it's pretty unlikely to hold for any length of time.