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  1. #1
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    Perenially loose cottered crank

    Hi, I have a 70s road bike that I'm trying to restore and get bike to riding condition. I have everything fixed except the left crank is loose. This is a cottered crank and I have replaced the original cotter pin, installed a new one, and after 5 minutes of riding it would get loose again. Then I would tighten and it would loosen in 5 seconds of riding. Both of these pins had a nice U shaped gash in them on the flat side after I removed them. I put a 3rd one in and didn't tighten it as much as I had the 2nd, and it worked for a day but it is starting to loosen already.
    The crank itself looks ok so I'm wondering if anyone has any suggestions. I'm a novice to bike repair but I've enjoyed fixing these problems.

  2. #2
    Senior Member
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    Take it to a bike shop that has a cotter pin press. Most people think they are only for removal, but a press is the best way to get them so tight they won't loosen up.

  3. #3
    Prefers Cicero cooker's Avatar
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    Quote Originally Posted by theloniouszen
    Hi, I have a 70s road bike that I'm trying to restore and get bike to riding condition. I have everything fixed except the left crank is loose. This is a cottered crank and I have replaced the original cotter pin, installed a new one, and after 5 minutes of riding it would get loose again. Then I would tighten and it would loosen in 5 seconds of riding. Both of these pins had a nice U shaped gash in them on the flat side after I removed them. I put a 3rd one in and didn't tighten it as much as I had the 2nd, and it worked for a day but it is starting to loosen already.
    The crank itself looks ok so I'm wondering if anyone has any suggestions. I'm a novice to bike repair but I've enjoyed fixing these problems.
    Sheldon Brown is an incredible bike resource person...here is some of his info on bikes cotters, which answers your questions. http://www.sheldonbrown.com/cotters.html

  4. #4
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    Now that i've done some research, I can also tell you it's a Centurion Le Mans.

  5. #5
    crusty old wrench
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    Cotter pins come in several different diameters, too. Try a larger one...

    Also, make sure that your crank and spindle are properly align with each other. The "U shaped gash" may be caused by a misaligment, which would also preclude a proper tightening.

    Use a hammer to drive in the pin, too. The bolt and htreaded shaft can easily break if they are used to pull the whole pin in.

    good luck...
    1 speed's all you need.

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