I'm rebuilding an older Mercier and have decided to tackle the bottom bracket. I've read a few articles and watched a few videos on how to remove the crank but none of them look anything like what I've got on this bike.

Basically, there are bolt threads on one side and a 'nub' on the other side that would indicate that this is what I would remove the crank arm with, but I'm not having any luck removing the bolt.

I've attached a picture as I'm sure I'm probably not using the correct terms for some of these parts.enter image description here

1 Answer 1


What you are looking at is called a "Cottered Crank". The shaped cotter pin holds the crank in place and they can be next to impossible to remove without significant effort or a cotter pin press.

Sheldon Brown has an excellent article on removing cottered cranks using a hammer and pipe, which is a method I have used before, albeit multiple decades ago.

When you get it off you may want to consider replacing the bottom bracket and cranks with a more modern design that is easier to maintain, unless this is a restoration job and you want to stay true to the original.

  • You will most likely destroy the cotter getting it out. Bring the cotter or pin to your local bike shop. They come in several sizes and matching it is easier if you have the old one.
    – mikes
    Commented Aug 17, 2012 at 19:54
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    Hmmm, I'm seeing the words "safe distance", "whale away" and "among the most challenging" from Sheldon. I think I'll take this one to the bike shop. It is not a restoration so a proper, modern design will be installed for sure! Thanks!
    – Jason
    Commented Aug 17, 2012 at 20:03
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    Yep, cottered crank, a scheme that largely disappeared about 35 years ago. A cotter pin press is ideal, and gives you some vague hope of not destroying the pin. Otherwise it's a lot of hammering, and possibly having to resort to drilling it out. Soak it for 2-3 days with Liquid Wrench et al before you tackle it. Commented Aug 17, 2012 at 20:04

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