Originally Posted by
HillRider
Gently? Come on, cotters need a LOT of force to remove and gently won't do it. The OP need to support the crank arm with a pipe or block of wood with a relief hole while whaling away with a BIG hammer to remove the cotter.
Well... cotters are pretty soft. Whacking it with a hammer with any amount of force will usually beat the threads to a pulp. Better make sure you have replacements in hand before you try it. They're pretty cheap:
http://www.bikepartsusa.com/bikeparts/item/01-98554/ . I think you have the most common size: 9.5mm diameter, but measure to make sure.