Problem with pedals


Old 01-09-02, 01:18 PM
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Question Problem with pedals

Here's the deal: my pedal cranks are set up in the manner of a simple bolt and nut. The nut has sort of a flattened side with ridges to, I assume, augment the friction. All of a sudden, the crank (on the opposite side of the chain) started coming loose. I seriously mean "all of a sudden," as I don't think have done anything to cause this. Anyway, now, however much I tighten it, it keeps coming loose when I ride it. Originally, being without any tools, I took it to a bike shop where they torque wrenched it to what I'd guess is the proper amount; still it came loose.

Any ideas (save getting a new bike)?

It's a not-too-old 18-speed. It's not in front of me right now, so I don't know the brand.
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Old 01-10-02, 02:32 AM
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Exactly how is your crank arm connected to the bike? Is there sort of a square peg coming out of the bottom bracket ( the joint at the bottom of the seatpost )? Does the crank arm have a square hole in it?

If so, try seating the crank by putting it on the square peg and hitting it with a mallot or putting a block of wood against it and hitting with a hammer. You don't have to wail on it, just try to seat it firmly. Next, take the nut that holds the crank arm on and tighten it. You may need a special tool ( that I forget the name of ) that fits over the nut like a socket, but is a bit thinner. A socket will probably be too thick to fit in the space between the sides of the nut and the hole in the crank arm where the nut goes.

If your crank arms are of a soft metal like an aluminum alloy, and if you rode any significant amount of time with the loose crank, you may not be able to fix it. The play introduced by the nut coming loose allowed the square hole of the crank arm to move back and forth over the steel peg and now the hole is probably not square anymore.

If you are able to tighten it but it continues to work its way loose, you could try shimming it with a piece of aluminum can or something. Just cut a small piece of aluminum ( about the size of one side of the square peg ). Put it inside the square hole of the crank, such that it is up against one side. Install crank as usual. That might help.

I had this same thing happen to me on a nice $1000+ bike. One crank arm worked its way loose and I waited too long to try to fix it. I tightened it a number of times myself before finally taking it to the bike shop. They determined that the hole on the crank did not match the peg anymore.

It should be possible to get a new crank arm relatively cheaply.

If your situation is not as I describe, post back with more details.
Old 01-11-02, 05:49 PM
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Halfway there...

Thanks for your help. The case is exactly as you have described. I tried everything you mentioned except shimming it before I posted this message--so hopefully, when I get around to it again, that will work.

Tightening it works for a little while before it comes loose again, so I don't think all hope is lost.
Old 01-14-02, 02:28 AM
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The main problem here is that if the square hole in the crank arm has been damaged, it will be difficult to keep the nut tight. With the square hole now slightly larger than the square peg, it will be very easy to introduce some play into the joint, thus loosening the nut.

If the shims don't work, I would do the following:

1. Take it back to the bike shop and have them tighten it again.
2. If it loosens back up, buy a new crank arm. You should be able to get a generic one pretty cheap. Either you can put it on or the bike shop can.

Good luck!
Old 01-17-02, 08:39 PM
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Unhappy The crank is done.

I attempted shimming it earlier today, but I have come to the conclusion that the crank is too far gone. Upon closer examination it became even more clear that the square-ness of hole is utterly destroyed. Thanks to all for the help, I will be going to the bike shop soon.
Old 01-18-02, 06:35 AM
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Sorry to hear that. It is exactly what happened to me

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