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Discussion Starter · #1 ·
just got a specialized allez and i've managed to bend the crank already or maybe it was bent when i bought it but it rubs up against the front deraileur in one spot, can this one be bent into shape or should i just buy a new one and can I throw any road bike double on their or do I need a specific one(i'm a roadie noob) I right now its an inhouse crank I think? sugino but i was thinking of slaping on a tiagra or 105 but didn't know if that would work, also I noticed that the shimano 105 cranks that are for sell on ebay look very different from the ones on shimanos own site ( different model, year or fake ?!?) has anyone had issues with ordering parts of ebay? :confused:
 

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?

Highly unlikely that a crank arm is bent. More likely possibilities:

- Crank arm is loose on the spindle, and therefore misaligned. You'd probably notice movement with this, though.

- Derailleur is misadjusted or crooked. Try straightening and then adjusting der. position.

It's really hard to bend a crankarm. It's one of the strongest and stiffest parts on a bike. It rakes a pretty good crash or similar accident. And you can't safely bend an aluminum part back into shape. The metal will be weakened dangerously.

Check your derailleur.
 

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Discussion Starter · #4 ·
yea sorry I meant the chain ring, I've been adjusting for hours and I can't get full range with out it scraping on the derailuer on one side or the other, I can also see where the chain ring very slightly bent went turning it
 

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Ah, you're likely right.

rkj__ said:
I think he is trying to say that the chainring is bent, and hence the rubbing on the front deraileur in one spot.

There is no need to buy a whole new crankset. The chainring likely can be bent back, or simply replaced.
And you're right that it can probably be fixed. Unless the spider is bent, it's fairly easy to bend a chainring back into shape, using a large adjustable wrench or an "inertial impact adjustment tool" (aka "hammer"). Even a bent spider arm can sometimes be straightened.
 

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hollandbk said:
yea sorry I meant the chain ring, I've been adjusting for hours and I can't get full range with out it scraping on the derailuer on one side or the other, I can also see where the chain ring very slightly bent went turning it
Here are some tips on addressing that:

http://www.sheldonbrown.com/straighten-chw.html
 

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Rubber mallet

hollandbk said:
think a good old rubber mallet to the chain ring will help? anything i need to be carefull of?
might do it. But check first whether it's the ring or the crank spider that's bent. And then (here's the thing to be careful of) remove the crank from the bottom bracket (if you need to pound the spider), or remove the ring from the crank, so when you pound on it you're not pounding the bearings.
 

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How to fix it

hollandbk said:
yea sorry I meant the chain ring, I've been adjusting for hours and I can't get full range with out it scraping on the derailuer on one side or the other, I can also see where the chain ring very slightly bent went turning it
I take it that you mean the CHAIN is rubbing on the derailleur, not the chainring rubbing on the derailleur.

Assuming that your BB is OK (i.e. not loose - it's extremely unlikely that it's bent), you have to straighten your spiders and/or chain rings. Hold a small screwdriver or other short, pointed object against the seat tube so that the tip just grazes the crank spiders as they pass. If the spiders are bent (most likely problem), you can even them out as follows:

Place the bike on its side with the crank supported on a block of wood at the axle. With another block of wood or a stout dowel placed at the end of the offending spider(s) give it a whack with a hammer. Check for change in alignment. If you got no change, hit it harder next time. Repeat until all the spiders are even. You may need to bend them away from the frame (brace the right crank on the block of wood) or toward the frame (brace the left crank).

Once the spiders are even, check the chain rings with the same technique except put the point of your screwdriver at the teeth of the rings (most likely the big ring only if the spiders are even). Straighten the chain ring by placing a large adjustable wrench over the ring with the jaws adjusted for a slip fit over the ring. Bend gently, and check alignment. Repeat until you've got it right.

Even with the chain rings dead straight, you still will get some deflection due to pedaling forces, but that should greatly improve your situation.
 
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