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Thread: Crank Problems

  1. #1
    Ogi
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    Crank Problems

    Alright, so I'm having some crank problems that require a little back story. Before winter I completed a fixed gear project from a crappy old Schwinn I found in my buddies garage because I didn't want to commute on my road bike. In order to fit a normal bottom bracket on, I had to use an adapter (because originally this thing had a one piece crank.) After a while of riding, my left crank arm came loose. A SRAM rep told me this was because after I had originally put the crank arm on, I tried to take it off, being a noob I had no idea I wasn't supposed to do this, and apparently messed up the crank arm. After learning this, I ordered another crank arm and rode around for a while, only to find that the new crank arm fell off after maybe four or five rides (I'm assuming because the original incident messed up the BB spindle.) Not having much time before the snow fell, I lost my will to fix this thing and put it in my garage. What I want to know now is, Im assuming I need to buy a new bottom bracket and crank arms, is there any chance that the adapter could have caused this to happen? I'm just making sure to cover all my bases before I go and order these new parts, because I don't want to have to keep replacing this. Can I just skip ordering these parts and use some sort of metal binding solution to essentially glue the crank arm onto the spindle? (my father who's a mechanic and originally got the bike sand blasted for me suggested this)

    Also, will a 9 and 10 speed chain whip work for an 1/8th inch cog?

    Thanks a lot in advance!

  2. #2
    Bicycle Repair Man !!! Sixty Fiver's Avatar
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    9 and 10 speed chain only works on 9 and 10 speed and is 3/32 with very thin outer plates... for a 1/8 cog you need 1/8 chain.

    Pictures are mandatory... can't see how a bb conversion for the Astabula bottom bracket could be causing problems if all was installed correctly.

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    Crank arms coming loose are typically a sign of a poorly installed crank arm. Square taper arms require a surprisingly large amount of torque to stay tight. Did you use a torque wrench for your installation or at least attempt to approximate the correct torque? If not, I can almost guarantee that's the cause of your problem.

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    Real Men Ride Ordinaries fuzz2050's Avatar
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    Joejack is right, 90% of the time a crank falls off, it's due to insufficient torque.

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    Quote Originally Posted by Ogi View Post
    ... A SRAM rep told me this was because after I had originally put the crank arm on, I tried to take it off, being a noob I had no idea I wasn't supposed to do this, and apparently messed up the crank arm. ...

    ... Can I just skip ordering these parts and use some sort of metal binding solution to essentially glue the crank arm onto the spindle? (my father who's a mechanic and originally got the bike sand blasted for me suggested this)
    I am not sure what you mean by "tried to take it off" and how this damaged the crank... maybe if you tried to take it off with a hammer and chisel instead of the proper puller...

    I also canot imagine how a BB adapter could cause a crankarm to fall off. More likely it was insufficient (or waaaa-aa-aay too much) torque.

    As for replacement parts, in my experience, it is possible to damage a spindle by riding with a damaged crankarm, but it usually takes quite a bit of effort (you would have to re-tighten and ride until it falls off several times).

    I have a set of Raceface LP crankarms I bought in the mid 90s, and they creaked from day 1 (installed with a torque wrench)... I use red loctite on the tapers (NOT on the bolt threads) and this keeps it from creaking until I take it apart again.

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    Ogi
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    It's not square taper, they're SRAM cranks that use the powerspline spindle, if that's relevant. I didn't use a torque wrench (still building my tool supply, but monies are scarce,) and I tightened as hard as I could. If I get a new bb and cranks is there a way to make sure this is done right without a torque wrench? Otherwise there's an LBS about 20 min from my house that has work stations for the public, they might have one. Is it possible to take the right crank off without messing it up? (have access to a puller) This way I could just buy a left new crank arm and a new bb and save a bit of money.

    Thanks for the replies everyone.

    Edit:
    Quote Originally Posted by LarDasse74 View Post
    (you would have to re-tighten and ride until it falls off several times).
    Yea, this is exactly what I did, I just had no idea it would further damage it, in hindsight this was extremely stupid, but I made more than a few dumb mistakes during the building process, including popping a tube because I didn't know I needed rim tape.
    Last edited by Ogi; 03-10-10 at 12:56 PM.

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