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  1. #1
    Senior Member deadsouls.'s Avatar
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    Problem with cranks.

    I'm still a newbie when it comes to bikes. So anyways I recently got a new bike off of BD, and i've done a little riding. But i realized that it looks like my crank arm is coming lose or something. I took the screw out but the thing just doesn't want to move. What should I do to fix this? Thanks.

    Here's a photo:
    Last edited by deadsouls.; 04-14-11 at 08:41 PM. Reason: photo

  2. #2
    headtube. zzyzx_xyzzy's Avatar
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    that's the way a crank on a square taper bottom bracket looks. Nothing wrong. You're going to have to replace the bolt and torque it to the right tightness though....

  3. #3
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    As zyzx says, if it's at all loose you need to tighten it properly. Looks don't matter, you can feel or hear a loose crank by a click and/or movement as it comes over the top and you press in it.
    FB
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  4. #4
    Senior Member deadsouls.'s Avatar
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    Thanks guys. I thought it looked different when I first got it, maybe not . Here I am hitting the damn thing with a hammer trying to push it in..

  5. #5
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    Quote Originally Posted by deadsouls. View Post
    Thanks guys. I thought it looked different when I first got it, maybe not . Here I am hitting the damn thing with a hammer trying to push it in..
    Keep this in mind for future reference.

    There are always more ways to make something worse than to make it better. So rule number one of mechanical work. if you don't know what you're doing, leave it alone, as the odds are against you.
    FB
    Chain-L site

    An ounce of diagnosis is worth a pound of cure.

    “Never argue with an idiot. He will only bring you down to his level and beat you with experience.”, George Carlin

    “One accurate measurement is worth a thousand expert opinions” - Adm Grace Murray Hopper - USN

    WARNING, I'm from New York. Thin skinned people should maintain safe distance.

  6. #6
    Senior Member Retro Grouch's Avatar
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    Hopefully you didn't ride it far enough that the crankarm is already hosed. Loose left crankarms with square taper bottom brackets is a common problem. The torque spec for crankarms is usually around 30 to 35 lb/ft. If you are tightening it with a 6" long allen wrench, you're not getting to 30 lb/ft.

    If the crank bolt isn't tight enough, the crankarm will eventually work itself loose and may even come completely off. Once that happens the square hole in the crankarm is usually hosed and the only adequate fix is to replace the crankarm. That happens often enough that every bike shop that I've ever worked in kept a stock of replacements.

  7. #7
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    Quote Originally Posted by Retro Grouch View Post
    If the crank bolt isn't tight enough, the crankarm will eventually work itself loose and may even come completely off.
    Yes - BUT:

    After a first-time installation with the proper torque, you may find that after riding a few 100 miles, the bolt will appear to have loosened. In fact, the bolt did not loosen, but the crank will have worked it's way further in. This is especially true if you greased the spindle square. (IMHO the only thing that goes against greasing!)

    If this is the case, do not retighten the bolt with the original torque - just retighten it to the point where you'd expect it (the bolt, not the crank!) not to come loose. Check repeatedly over the next few 100 miles.

    Quoting Jobst Brandt:

    >Failure from "over-tightening" is caused by repeated re-tightening of properly installed cranks. In use, an aluminum crank squirms on its taper and, because the retaining bolt prevents it from moving off the taper, it elbows itself away from the bolt and up the taper ever so slightly. The resulting loss of preload, after hard riding, can be detected by how easily the bolt can be turned.
    ...
    Mechanics, unaware of why crank bolts lose preload (and commensurate crank tightening), have re-tightened bolts until cranks split. No warnings against re-tightening properly installed cranks are evident although it is here where the warning should be directed rather than at lubrication.<

    Full text:

    http://www.sheldonbrown.com/brandt/i...ng-cranks.html

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