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Old 05-08-11, 11:20 PM   #1
DerpDerp
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Crank arms moving separately from chain ring

First of all, I need to apologize for the title - it was the best way I could summarize it. Also, I'm clueless when it comes to mechanics.

Today after riding to the ATM and back, I tried practicing some skids and trackstands on my fixed gear. While I was trackstanding, I noticed my crank arms were budging much more than they normally do when the chain's being pulled tight from a acertain crankset position. I de-saddled and played with my arms, and to my surprise I was able to push my crank arms independently of the chain ring.

The crank arms move as a unit, about 2 or 3 mm in either direction I push on it with my hand. I did a search on this topic, some of them said I need to get a new bb or a new crankset because the square taper might become rounded.

If someone could shed more light on this information I would greatly appreciate it. I'm using Origin 8 Propulsion cranks if anyone needed to know.
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Old 05-09-11, 02:31 AM   #2
dabac
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Originally Posted by DerpDerp View Post
..I tried practicing some skids and trackstands on my fixed gear..., I noticed my crank arms were budging much more than they normally do when the chain's being pulled tight from a acertain crankset position... to my surprise I was able to push my crank arms independently of the chain ring... I'm using Origin 8 Propulsion cranks.
If yours are like these, I find it hard to see how that can happen. The spindle that carry the chain ring is cast in one piece with the right crank arm.
The left arm may wiggle a bit independently from the right, which usually means a rounded out square taper and that a replacement is due. You can try tightening the crank bolts up properly first. If you've caught the wiggle early enough this may fix it. But don't hold your breath.

Pretty much the only option for what you seem to be describing is if your chainring bolts (the bolts that hold the chain ring to the arms of the right crank) are all about to come off/are seriously messed up. Should be easy enough to check.
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