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Thread: Crank Wobble?

  1. #1
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    Crank Wobble?

    Built a conversion from an old KHS road frame and parts from my LBS about a month ago. Ive been getting what seems to be some left-right movement in my right crank. I find that after I ride I need to re-tighten the crank bolts, almost a full rotation.
    Origin-8 crank and chainring
    salvaged the old pedals
    KMC chain
    Sugino BB

    It only happens at the top of the rotation (when my right foot is nearest to the top tube)
    Any help would be greatly appreciated

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    I assume they're square taper interface... Your crank arm might be bottomed out. If the spindle is going too far in, because the hole in the crank arm is worn out, then the bolt can't actually fully tighten against the crank. This will make your crank arm wiggle, and will back the bolt out as you ride.
    You might not be able to see that your crank is messed up, because it might not be rounded out at all, just stretched from over-tightening.

  3. #3
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    this happened to me a while ago. I had to replace the crank arm and BB because I went too long tightening the crank arm after every ride. by the time I got it fixed the whole inside of my crank arm was destroyed, it was almost completely rounded, and my BB was all rounded as well. get it fixed now and you may not need to replace your BB, only your crank arm.

  4. #4
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    Stop tightening it. Your crank is DONE. Finished. Toast.

    If you are having to tighten it after every ride, then the square taper interface is most likely distorted. It oculd be hollowed out or stretched out like the previous posters said. This happened to me once. You are going to have to get a new crank, there is really no 2 ways about it, sorry man...

    BUT, if you stop riding it now, you can save your BB spindle. The BB spindle is made of hardened steel while the crank is made of aluminum. The crank will hollow out long before the BB gets rounded off. You can, however, destroy the BB spindle if you keep riding it w/ a messed up crank. That's why I suggest you stop riding this crank, replace the crank, and hopefully you can keep the BB. Good luck.

    EDIT: When you get a new crank, make sure that you install it properly. This means using a torque wrench and tightening the crank arm bolts to spec. A good LBS should do it this way.
    skinnytire

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    Wow... pretty lame...
    These parts are basically brand new, is the LBS/manufacturer at fault or did i do something wrong in the first place?

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    its probably a combination of improper initial installation and poorly manufactured parts.. as much as I love that origin8 has decent parts for cheap(and everything matches) theyre still cheaply manufactured.

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    This is pretty disappointing
    So I have to go in to my LBS and drop another 40-60$ on new cranks just 4 weeks after i did that exact same thing?
    Can you recommend better cranks or tell me what i can do to prevent this next time?

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    try out the sugino messenger cranks, I used to have them on another bike. they worked very well.

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    Yeah, Sugino cranks are pretty good for the price. I've bought a couple sets of them, used, from a bike shop I trust, and have had no complaints.

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    Quote Originally Posted by Velocityraptor View Post
    This is pretty disappointing
    So I have to go in to my LBS and drop another 40-60$ on new cranks just 4 weeks after i did that exact same thing?
    Can you recommend better cranks or tell me what i can do to prevent this next time?

    After you install them, check them every couple miles for first couple days, then periodically after that. I'd just go with a old set of Shimanos, can be had for like 10-20 bucks used.

    It's dissapointing, but easy and somewhat cheap to fix... May ybe I can cheer ya up with this: A couple weeks ago I finished a 3 month long project, which was rebuilding the transmission and top end of my '67 Triumph... I blew the motor 10 miles into my shakedown run after completion and intial bench-tuning because I forgot to double check one tolerance... now I get to dump 5 Kilo TT's worth of cash into parts and machine work and hosed 2 Kilo TT's worth of brand-new parts.
    Last edited by ianjk; 07-13-09 at 04:06 PM.
    Quote Originally Posted by Santaria View Post
    because physics has more street cred than tarckstars.

  11. #11
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    if you get the new crank installed correctly it shouldn't be a problem again.

    Also, if LBS installed them originally I would tell them what happened. They might be willing to do a free replacement.
    skinnytire

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