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Thread: Cottered Crank

  1. #1
    Uber Goober StephenH's Avatar
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    Cottered Crank

    If you hand-fit a cottered crank together, how much farther will the pin move when fully installed?
    In other words, how do you know if you need to file it down any without driving it in, then back out, then repeat, etc?

  2. #2
    Your mom
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    It should not move too much more. I've learned this the hard way. Pre-fit should be nearly where it sits when finally seated. Of course, someone who's done more of them is probably going to contradict me.

  3. #3
    loser
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    sheldon brown suggests that tightening the nut won't get it tight enough.

    go here and scroll down.

    Good luck!

  4. #4
    My bikes became Vintage OLDYELLR's Avatar
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    You have to hammer it (or use a press) before tightening the nut. If you have cottered cranks, it's good to have a good supply of these cotter pins (just like the other cotter pins [split pins in British parlance], they're expendable).
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    Uber Goober StephenH's Avatar
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    Thanks, y'all.

    I had read the Sheldon Brown articles, otherwise it wouldn't have occurred to me that they might need to be filed- I would have just assumed they had to go in far enough to get the nut on. (Right now, with hand assembly, you can't even start the nut on the threads, so unless they move a good 1/4", the nut won't be fully on.)

  6. #6
    Healthy and active twobikes's Avatar
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    Cotters were once cheap and ubiquitous, but now are hard to find locally. I needed a new one, but did not have any and did not want to wait until I could get some by mail order. The threads were stripped on an old one. I cut off the threaded portion and welded a 1/4" x 20 thd/inch stud to the body of the old cotter. It worked very well. I now have more than 1,000 miles on that welded cotter with no problems. If you have access to a welder, it is also possible to build up the flat surface on a cotter and file or grind it to a new configuration.
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    Where do you mail order your cotters from? I haven't had any luck finding any and I might need some soon.

  8. #8
    Healthy and active twobikes's Avatar
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    You can get them from Harris Cyclery in West Newton, Massachusetts, which is where Sheldon Brown is based. Here is a link to their page on cotters. You probably want the 9.5 mm (3/8") size.
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