How to Replace a Cottered Crank

Mount the bicycle securely in a stand so that the cotters are easy to get to. The cotters are small pins that are pressure-fitted into holes in the crank arm, then tightened and held in place by a nut. Remove this nut and its washer before attempting to remove the cotter.

Start with a cotter press if one is available. You can buy a press online from BikesmithDesign for about $60 including shipping as of January 2010. At one time Park Tool made a press for removing cotters; you might find one of these on the used market. Line up the press on the cotter pin, attach a wrench then tighten the press to push the cotter out of the crank arm.

Use the hammer method if a press isn't available. The late bicycle mechanic/repair guru Sheldon Brown favored the carpenter's claw hammer over the ball-peen hammer for this purpose. He said the trick was to line up the hammer and deliver a good heavy blow to the cotter to drive it out rather than tapping at it with successively harder blows.

Move to a punch and hammer combination if you have a really stubborn cotter. Hold the punch with a pair of pliers and deliver a sharp blow with the hammer. If the punch method isn't working, try drilling the cotter out with a 1/4-inch drill bit. Drill the length of the cotter so that the pin will collapse and be easier to drive out with the punch.

Heat the cotter pin with a propane torch if nothing else is working. Don̵7;t overdo it: get the cotter to a point where it is too hot to touch but not hot enough so that the metal begins to change color. Then drive the pin out with a hammer or hammer and punch combination.

Save the cotter pin for reuse if you were successful in removing it with the press or a few quick hammer blows. Look for any grooves that have been cut into the body of the pin by the axle. If grooves have been worn into the pin, you should replace it. Check online with BikesmithDesign or HarrisCyclery for replacement cotter pins.

Install the cotter by inserting it into the hole and tapping its blunt end with a hammer. The pins are tapered, and the taper should be reversed on the opposite crank arms. Once the cotter is through the hole far enough, place the washer and nut onto the pin. Tighten the nut, then tap the cotter pin, tighten the nut again and continue until the cotter is tight. Don't tighten too far because the cotter is made of soft metal, and you can easily strip the threads if you get it too tight.