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Thread: Broken crank!

  1. #1
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    Broken crank!

    Well I've broken my 1st crank, I was climbing a short steep hill and suddenly the left pedal felt all wobbely, I thought my cleat came loose. After 4 years of racing and riding I guess everything will eventually break (Bontrager Select from 2002 Big Sur):
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    Note that this proves that aluminum does NOT have an infinite life like steel does regarding repeated loads which are all applied with a force well below their yield strength. Sorry, that was the mechanical engineering degree talking. What I meant to say was: Wow, dood That's wicked awesome! You ah like SO my freekin' hero!

    Ian

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    niiiice


    is the crank solid the whole way through?

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    Ya it's solid.

  5. #5
    CURB HUCK!!!!!!
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    WOW, think about all these new hollow cranks out, i wonder what kind of life they're going to have
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    about the same as a solid crank because the material close to the neutral axis has very little effect on the strength.

  7. #7
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    Quote Originally Posted by frknlitebike
    about the same as a solid crank because the material close to the neutral axis has very little effect on the strength.
    Agreed. That failure is likely the cause of a surface ding / gouge that eventually carried through.

    Given the condition of the crank arm (pretty banged up all around), this isn't so inconceivable. However, given the location of the start of the failure (on the "backside" of the non-driveside crank, close to the bottom bracket), that's pretty friggin' odd.

    AJ, do you recall any significant dents or scratches in this location prior to the failure? Honestly, that's creepy! How'd you ride out?
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    possibly a hard landing with the cranks horizontal and taking all the body weight caused the initial stress?


    I have to say, i've never considered a crank as a fail component if you know what i mean. I've always assumed the frame would break first.

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    Quote Originally Posted by Speedub.Nate
    Agreed. That failure is likely the cause of a surface ding / gouge that eventually carried through.

    Given the condition of the crank arm (pretty banged up all around), this isn't so inconceivable. However, given the location of the start of the failure (on the "backside" of the non-driveside crank, close to the bottom bracket), that's pretty friggin' odd.

    AJ, do you recall any significant dents or scratches in this location prior to the failure? Honestly, that's creepy! How'd you ride out?
    There is a small ding that is 2mm away from the start of the crack.
    No large or noticeable dings where the crack started.

    I do find it odd the crack is 40 mm from the centre of the bottom bracket and it is a 175 mm crank. What I mean is it is so close to the centre, you would think it would crack further out.

    I rode with one leg when I was on the flats and walked up the hills. The crank is actually still quite solid - I can't bend it with my bare hands.

  10. #10
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    My LX hollowtechs from 2002 with 12000km on em just gave way. The spider is moving around 2-3 mm on the crank... So yea there is another example of fatiguing cranks

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