Quote Originally Posted by Trek420
What are Cottered cranks?

I think I know but don't want to sound dumb when I go in to the LBS to talk about the freewheel fixer upper.
It's a way of attaching the crank arms to the bottom bracket spindle with metal pins about 8-9 mm in diameter. One side of the spindle shaft is flattened to match the flat tapered part of the pin. You slide on the crank arms, put the pin through the hole in the arms so the flat side of the pin matches the spindle flat, pound them in lightly, and screw on a nut. Often they would get munged after lots of riding and then the crank arms would develop play. Or they would get stuck and be really hard to get out. And everytime you removed them you had to readjust the front derailleur because the crank ended up in a slightly different place. Sure glad they are a thing of the past. But if you've got an old Motobecane Mixte from around 1970, it probably has them.

Here's a page from Sheldon Brown:
http://sheldonbrown.com/cotters.html