Shimmed crank = dangerous?

Discussion in 'Cycling Equipment' started by Art, Apr 16, 2003.

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  1. Art

    Art Guest

    I had to put a shim under my crank in order to get it to tighten up properly. I cut a small shim
    from a coffee can lid, and bent it to cover 2 adjacent sides of the square taper crank.

    Is the crank more likely to fail now?

    Art
     
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  2. Raymo853

    Raymo853 Guest

    I am not sure, but that just not sound safe to me. I could see the crank coming loose, see it
    cracking because the bulk of the pressure is on two sides instead of distrubuted among four and so
    on. just go buy a properly sized BB.

    "Art" <[email protected]> wrote in message news:[email protected]...
    > I had to put a shim under my crank in order to get it to tighten up properly. I cut a small shim
    > from a coffee can lid, and bent it to cover 2 adjacent sides of the square taper crank.
    >
    > Is the crank more likely to fail now?
    >
    > Art
     
  3. Don Holly

    Don Holly Guest

    Don't know if the crank is more likely to fail, but so far I've put about 20,000 miles on my crank
    with a similar brass shim.

    Don

    Art wrote:
    > I had to put a shim under my crank in order to get it to tighten up properly. I cut a small shim
    > from a coffee can lid, and bent it to cover 2 adjacent sides of the square taper crank.
    >
    > Is the crank more likely to fail now?
    >
    > Art
     
  4. "Art" wrote:

    >>I had to put a shim under my crank in order to get it to tighten up properly. I cut a small shim
    >>from a coffee can lid, and bent it to cover 2 adjacent sides of the square taper crank.
    >>
    >>Is the crank more likely to fail now?

    An anonymous hotmail user wrote:

    > I am not sure, but that just not sound safe to me. I could see the crank coming loose, see it
    > cracking because the bulk of the pressure is on two sides instead of distrubuted among four and so
    > on. just go buy a properly sized BB.

    This isn't about the BB size, it's about salvaging a crank that has a damaged tapered square where
    it fits on the spindle.

    I don't consider this to be a "professional-type" repair, but have occasionally done this, mainly
    on charity cases, or with irreplaceable cranks. I use aluminum beverage cans as the shim material,
    it's more malleable and easier to work with than the steel "Art" used, and the crank, after all,
    is aluminum.

    I've actually never known of any failure from this, it really seems to work pretty well, even on
    cranks that are otherwise toast.

    It's not true that this concentrates the pressure on two sides. The taper angle remains unchanged,
    and all 4 sides bear equally. The crank is moved off center by half the shim thickness, but this is
    negligible.

    Sheldon "In A Pinch" Brown +---------------------------------------------+
    | I am not young enough to know everything. | -- Oscar Wilde |
    +---------------------------------------------+ Harris Cyclery, West Newton, Massachusetts Phone
    617-244-9772 FAX 617-244-1041 http://harriscyclery.com Hard-to-find parts shipped Worldwide
    http://captainbike.com http://sheldonbrown.com
     
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