Removing a cottar pin is usually a simple task. You just straighten the tangs and pull the cottar pin out of its hole. Sometimes, rust and dirt combine to tightly lock the cottar pin in the hole. Tools and techniques help, but it can seem impossible to remove the pin.
Removing a Stuck Cotter Pin
Use a cottar pin removal tool--resembling an awl with a bent tip--to loosen a stuck pin. Insert the tip through the loop of the cottar pin and pull the pin out. While pulling on the remover's handle, use the bend in the shank as a fulcrum to increase the pulling power of the tool. Straighten or cut off the tangs of a stuck cottar pin before attempting to remove it.
Instead of a removal tool, you can use a nail and a small screwdriver or a small punch.
Use a hammer and punch if the removal tool fails to extract a stuck cottar pin. Cut or break both ends of the cottar pin flush with the bolt or shaft and use the hammer and a punch to push the remainder of the pin through the hole. The punch should be the same diameter as the pin or slightly smaller.
If the cottar pin is so stuck that no amount of pulling or hammering will remove it, there are two remaining options. Drill out the stuck cottar pin slowly and with minimal pressure on the drill to avoid breaking the bit. The second option is to simply cut off the loop and the tangs and unscrew the nut. This can damage the threads of the bolt and should only be used as a last resort.