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Loose Crank Arms

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Loose Crank Arms

Old 10-15-09, 11:36 PM
  #26  
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Let me try and clear some things up...

Excuse me for lacking the needed descriptions. Let me try and clear some things up:

The problem is with the cranks, not the BB. The become loose axially (so long as that's the right word to describe movement perpendicular to the bicycle). And I need to re-tighten the bolt because it works loose.

The cranks are two weeks old. They were new when I got them. I also think it's too early to think that the cranks are broken. Forget getting new cranks for now: I'm going to take these to the LBS before I decide I need new ones. Also, I see operator's point, and that a different interface won't fix the problem. (I wasn't thinking about my problem much when I said that.)

But, for reference for the future: what can I do myself?
When installing my cranks, I did grease them. I know some people say to not grease square-taper interface, but I think that's ridiculous, especially after reading a particular article on Sheldon Brown's website. I use a ratchet, though it's not an 18" (as suggested by DannoXYZ). I haven't much experience with tightening things to a measured torque, so the best description I can give is, "I tightened them 'thoroughly.'" I intend on getting a torque wrench for my personal bicycle-repair in the future because of this incident.
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Old 10-15-09, 11:57 PM
  #27  
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Well, if the crank taper has been ovalized or flatened and the LBS won't do anything for you, THEN I recommend using the loctite(service removable only).
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Old 10-16-09, 12:06 AM
  #28  
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Originally Posted by H3llM4rine
The cranks are two weeks old. They were new when I got them. I also think it's too early to think that the cranks are broken.
Sadly, no. It is not too early.

The taper in a crank must be a very precise fit with the taper on the spindle. If there is any deviation from this shape, cranks are likely never able to stay tight again - they develop a microscopic amount of movement and slowly ratchet off the bolt; the shape of the crank taper becomes further damaged as the bolt comes off and the ratcheting speeds up; which accelerates the damage to the crank.

Overtightening your cranks during installation will mess the taper up waaaaay faster than that, but the result is the same.

I have hear of using shim stock to revive damaged cranks, but I have yet to see it work. I am not saying it doesn't work, just that I have never seen it work.

You may be able to use locktite or something but I cannot say for sure. I have used red locktite successfully to quiet squeaky crankarm/spindle interfaces when the ratcheting action is still very minor, but not for overtightening damage.

If a crank is repeatedly retightened and ridden, damage to the BB spindle can result and may damage subsequent crank arms, so sometimes the BB spindle must be replaced too.

Edit: if you decide to try red loctite (262?), use it on the crank taper only! Do not put permanent strength loctite on your bolt threads! Use blue loctite (242?) for that.

Last edited by LarDasse74; 10-16-09 at 12:12 AM.
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Old 10-16-09, 12:18 AM
  #29  
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The ratio of crankarm replacements to bb spindle replacements is about 10000:1.
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Old 10-16-09, 12:42 AM
  #30  
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Yeah, there's absolutely zero way the soft aluminium crankarm can damage hardened steel on the spindle. That crank is toasted.
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Old 10-16-09, 06:51 AM
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Originally Posted by DannoXYZ
Yeah, there's absolutely zero way the soft aluminium crankarm can damage hardened steel on the spindle. That crank is toasted.
I have seen it happen... the rider continues tightening and riding and retightening for a long time and the crank 'polishes' the edges of the spindle just enough to make a correct fit with a new crankarm impossible. It is rare but it happens.
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Old 10-16-09, 07:03 AM
  #32  
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Once you've ridden with them loose, you may have damaged them. Seriously not fun breaking a crank.
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