Cottered cranks

Never needed a cotter press in my bike-fixing life - which goes back to 1952.

The secret to getting them out isn't complicated:
1: Undo nut, remove washer. Spray both ends with penetrating oil or WD40. Leave for some hours.
2: Replace nut, without the washer. But leave it loose, so its top face is level with the end of the pin.
3: Remove the bike's wheels.
4: Find a steel tube (I use a tube spanner) that is a loose fit around the head of the pin, and longer than half the diameter of the chainwheel.
5: Perch the bike on the tube, so the head of the cotterpin is inside the end of the tube, and the bike's weight is sitting on the crank head, on the tube. Which is on a solid concrete floor.
6: Take a large round punch, that covers both the end of the pin thread, and the nut.
7: Hit it once, VERY hard, with a 2lb. hammer.
8: Remove the nut (this will ease out any thread distortion caused by the punch)
9: Continue with the punch, directly on the cotterpin. It should now come out without much more force.

NB. Yes, as you'll have noticed, this does need four hands. So you need an assistant.

The key point is to take the force of the hammer-blow directly from the crank head to something solid, NOT passing it through the bb bearings and the frame. Apart from wrecking the bearings, that robs the hammer-blow of most of its impact force.

If you have to do this frequently, there are two more specialised methods:

1: Make up a ''closed sleeve nut'' - that screws onto the cotter in place of the normal nut, is closed at the top, and is slim enough to fit into the cotter-hole in the crank head. Make sure the thread in the nut has enough 'headroom' that the end of the nut bears directly onto the unthreaded shank of the cotter.

2: Use an ultrasonic driver, holding it directly on each end of the pin in turn.

 – remember Doctor Who's Ultrasonic Screwdriver?  Well, this is it!