Cottered Cranks

Really old bikes use cotter pins to secure the cranks to the bottom bracket spindle, and they can be a little tricky to remove and install. I'll show you my C-clamp method. I think it's pretty simple, and a big C-clamp is a lot cheaper than a cotter press. Consider a large hammer as a last resort option, since it will ruin the cotter pins and can even damage the bottom bracket.

You'll need something to use as a spacer between the crank and the clamp. I like to use a worn out 1/2" socket, but any piece of metal that's at least half an inch thick with a big enough hole going through it should work. The purpose of this spacer is to transfer the clamp's force to the crank rather than the top of the cotter pin, allowing the pin to pop out the other side.

Removal:
To remove a cotter pin, first unscrew the nut until it is flush with the end of the threads. Leave it on however, because the threads are the weakest part of the pin and are likely to bend if they're left unsupported:

Now place the spacer over the round part of the pin and position your clamp over the pin:

Tighten down the clamp until you feel a "pop". This means the cotter pin is free. Now you can remove the nut and pull the pin out of the crank. You might have to push it the rest of the way out with the clamp if it's still tight. Edit: I did have one pin that wouldn't come out no matter how much force I put on the clamp. I removed it by striking the clamp with a hammer in the direction that the pin had to come out. With the added force of the hammer on the clamp, the pin finally popped right out without any damage.

 

With the cotter pin out, the crank should slide right off. If you've been riding around with loose cotters for a very long time you might have to tap the crank off with a hammer if it still won't come off (don't ride with loose cotter pins).

 

Installation:

Installation is the reverse of removal. You will press the pin in from the smooth side, so now you'll have to put the spacer over the threaded end (the nut won't be needed just yet). The flat side of the pin should contact the flat side of the spindle. The pins should also be installed pointing oppositely on either crank so that the crank arms will be 180 degrees apart.

Press the pin in really nice and tight. Remember, it's transmitting all of your pedaling force to the spindle. Only after you pressed the pin tightly into the crank should you install the nut. Never try to use the nut to pull the cotter into the crank (unless you like breaking pins and making life really difficult)..

 

The retaining nut should only be snug tight, since its only job is to hold the pin in place. Cotters are made of soft metal, so the threads won't withstand a lot of force. This is why you can't tighten a loose cotter pin just by tightening the nut.
 

Damaged pins should probably be replaced in pairs to be sure that the cranks stay in the right positions. You might also want to file down any burrs or wear marks on the tapered part of the pins to ensure they will fit properly. You might want to press in your cotter pins one more time after riding around for a while to make sure they remain tight. I've personally had some bad experiences with loose cotter pins which is why I dislike them, but a properly installed set of pins should be trouble free.