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Bicycle Mechanics Broken bottom bracket? Tacoed wheel? If you're having problems with your bicycle, or just need help fixing a flat, drop in here for the latest on bicycle mechanics & bicycle maintenance.

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Old 09-14-10, 09:28 PM   #1
TheManSuit
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Bent Shimano 600 crankset???

Alright, a few months back I received a very lovely Cannondale SR300 with a full Shimano 600 tricolor group. In my excitement, I decided to use some of the parts I had acquired on a commuter bike I received not too long afterwards, such as the crankset. Unfortunately, I noticed something rather odd about the chainrings: they wobbled rather abrasively no matter how many times I took the crank off and put it back on.

At first I thought it was just bent chain rings, until I took off the outer and realized it was straight as an arrow. The smaller ring & crank also look to be rather straight. However, putting it back together and installing it on another BB, I experienced the same problem.

It almost appears as if the crank isn't sitting straight on the BB, even though I am very carefully installing it. I'm starting to think that perhaps the square tapers just aren't working with the crank, but I have another identical crank set that works just fine (there is only a little play in the chain, from what I assume to be as a result of the Biopace engineering).

Without much knowledge on fitting cranks to BB's or how to identify subtle issues on cranks, I'm kind of at a loss. Does anyone have any information they could lend me to help me get to the bottom of this mess? I really don't want to throw it out.

Thanks!
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Old 09-14-10, 11:57 PM   #2
Jeff Wills
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Originally Posted by TheManSuit View Post
Without much knowledge on fitting cranks to BB's or how to identify subtle issues on cranks, I'm kind of at a loss. Does anyone have any information they could lend me to help me get to the bottom of this mess? I really don't want to throw it out.
It sounds like the spider is bent on the right crank. This can be straightened by a good mechanic, but it's probably better to replace the crankarm. And, yes, I realize it's tough to find those arms.
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