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Thread: Loose crank

  1. #1
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    Loose crank

    I just had work done on my mountain bike (Trek 4500, about 3 yrs old) because the chainrings were coming loose from the crank. I think it was a loose spider ring maybe? Anyway, they tightened it up for me and charged 10 bucks and everything was good. 12 miles of riding later (after a few weeks) my right side crank comes loose. The hex bolt holdin on the crank (I assume that's what it does) is really loose. So I'm thinking that it's the LBS's fault because I've ridden the bike for years w/ no trouble, then they do some work (assuming they took the crank off to tighten the lockring) and it almost falls off 12 miles later. So I guess I'm kinda complaining, but I also want to know what to do. I'd take it to the shop, but that's a hassle and I guess it might not be their fault, so what do I need to do to fix it myself. Can I just tighten it back, or do I need to worry about sand/dirt having gotten inside somewhere, and then take it all apart, clean it, and put it back together? I pretty much stopped riding when I realized something was wrong, but it was a pretty sandy trail. And, can I just tighten the bolt down real tight, or does it really need to be a specific torque? Thanks, and sorry for the long message.

    -Will

  2. #2
    Senior Member iowarose's Avatar
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    Speaking from the customer's perspective, I would certainly take it back to the LBS and point it out to them.

  3. #3
    Reckless Rider trlpmp's Avatar
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    Tighten the bolt down with wrist-not arm. If it comes loose again tighten it a little more than the last time.
    Did you miss it?

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    Senior Member sydney's Avatar
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    Quote Originally Posted by trlpmp
    Tighten the bolt down with wrist-not arm. If it comes loose again tighten it a little more than the last time.
    And you can get 35 foot pounds that way?? It needs to be tight enough that is does not come loose again.That may have been the issue to begin with. Loosening while riding it can hose the crankarm interface.

  5. #5
    Listen to me powers2b's Avatar
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    Go back to the shop and ask for your $10 back.
    They are liable for work that they do to your bike and would rather give your money back than face a bad image and/or lawsuit.
    Enjoy

  6. #6
    Senior Member sydney's Avatar
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    Quote Originally Posted by sirwilliamjr
    I just had work done on my mountain bike (Trek 4500, about 3 yrs old) because the chainrings were coming loose from the crank. I think it was a loose spider ring maybe? Anyway, they tightened it up for me and charged 10 bucks and everything was good. 12 miles of riding later (after a few weeks) my right side crank comes loose. The hex bolt holdin on the crank (I assume that's what it does) is really loose. So I'm thinking that it's the LBS's fault because I've ridden the bike for years w/ no trouble, then they do some work (assuming they took the crank off to tighten the lockring) and it almost falls off 12 miles later. So I guess I'm kinda complaining, but I also want to know what to do. I'd take it to the shop, but that's a hassle and I guess it might not be their fault, so what do I need to do to fix it myself. Can I just tighten it back, or do I need to worry about sand/dirt having gotten inside somewhere, and then take it all apart, clean it, and put it back together? I pretty much stopped riding when I realized something was wrong, but it was a pretty sandy trail. And, can I just tighten the bolt down real tight, or does it really need to be a specific torque? Thanks, and sorry for the long message.

    -Will
    I'd take it back.You can retighten it. Problem is that having it loosen up while riding could have damaged the crank.When that happens, it will often never stay tight.

  7. #7
    cab horn
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    They charged 10 bucks to tighten a couple screws...? Or am I missing something.

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    Senior Member peripatetic's Avatar
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    Quote Originally Posted by sydney
    I'd take it back.You can retighten it. Problem is that having it loosen up while riding could have damaged the crank.When that happens, it will often never stay tight.
    Exactly this happened to me. I rode on a loose crank maybe 1/2 mile total. Took it in, the mechanic took off the crank and showed me how the soft metal of the crank had worn out by rubbing loosely against the harder-metal spindle. I had to replace the crank and pay for the labor. Totally ruined my day. Take it back to the shop and make sure that the crank isn't really messed up. If it is, they should replace it for free and tighten everything down better.

  9. #9
    Senior Member midgie's Avatar
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    Definately take it back to the shop. If you try to tighten it your self, and have to do this numerous times, with the same outcome, and then you take it back to the shop . They will not stand behind it. Riding a loose crank will round out the crank and possibly the the BB spindle. Then you'll have to replace both. Crank bolts should be tightened with a torque wrench, to insure that the arm is on all the way, and that it will stay there. IMO
    We're gonna have the hap, hap, happiest Christmas since Bing Crosby tap-danced with Danny ****ing Kaye.~Clark Griswold

  10. #10
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    Well, I took it by the shop today and talked to the mechanics. They said that it isn't uncommon for crank bolts to come loose once you've loosened them the first time. Doesn't make a whole lot of sense to me, but they were nice about it and tightened it up for me (for free). I asked if it could have gotten messed up riding w/ it loose, but they said the splines on mine (don't know what type of cranks I have) are really hard to mess up and it should be fine. I took his word for it, and I rode it a little and it seemed fine, so I'm happy. I guess time will tell if I've been screwed though... Thanks everyone for the help.

    -Will

  11. #11
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    Maybe use some blue loctite? Prevent from happening again.

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