Bent chainring or bent spider?
11-22-15, 04:30 AM
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Bent chainring or bent spider?
I crashed on the non drive side and a following rider rode over me. It seemed the large chainring on my Ultegra 6700 crankset was bent but the small one was okay. I tried to bend it back with a wrench but it was cracked.
I bought a used chainring and installed it but it is still not straight. I can see the teeth on the side opposite the crankarm go in towards the frame slightly, enough that the chain won't ride smoothly on all the teeth while pedaling. The chain will sometimes slip to the outside of the chainring instead of sitting on the teeth in that area.
The small chainring seems to track straight. Is the used chainring I bought bent or is one of the arms on the crank spider bent or both? Can the spider be bent such that the inner ring is straight but the outer ring isn't? What's the best way to check the spider? Thanks!
I bought a used chainring and installed it but it is still not straight. I can see the teeth on the side opposite the crankarm go in towards the frame slightly, enough that the chain won't ride smoothly on all the teeth while pedaling. The chain will sometimes slip to the outside of the chainring instead of sitting on the teeth in that area.
The small chainring seems to track straight. Is the used chainring I bought bent or is one of the arms on the crank spider bent or both? Can the spider be bent such that the inner ring is straight but the outer ring isn't? What's the best way to check the spider? Thanks!
11-22-15, 06:21 AM
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Rotate the chainring and see if the problem spot follows the spider or the chainring. Any problem with the spider will affect the big ring more than the little one.
11-22-15, 06:29 AM
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Remove the chainring and lay it on a flat surface to ensure that it's dead flat. Measure from each spider arm to a fixed point on the down tube or seat tube.
11-22-15, 07:18 AM
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Since the problem has showed up with 2 different chain rings, I'm going to bet you have a bent crank spider arm. It should be relatively easy to figure out which arm is bent. Since you aren't satisfied with the way that your bike rides now, you have nothing to lose. Clamp a big adjustable wrench over the bent arm and try to bend it back. If it works, great. If it doesn't, the alternative is replacing the crank set.
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11-22-15, 07:31 AM
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Since the problem has showed up with 2 different chain rings, I'm going to bet you have a bent crank spider arm. It should be relatively easy to figure out which arm is bent. Since you aren't satisfied with the way that your bike rides now, you have nothing to lose. Clamp a big adjustable wrench over the bent arm and try to bend it back. If it works, great. If it doesn't, the alternative is replacing the crank set.
11-22-15, 09:03 AM
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Even easier. Now all you have to do is to find a source for the shims. I'm thinking google is your friend.
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11-22-15, 10:28 AM
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Not especially cheap, considering they are stamped aluminum or stainless, but a lot less that a new crankset. Your LBS should be able to order them, too; mine did.
