I removed the pins on my cottered crank by loosening the nuts so they were flush with the threaded part, tapping with a hammer to get them lose, remove nuts and press out the rest of the way with my thumb. Install was press the pin in as far as I could and use the nut to draw it the rest of the way. I never had to replace a pin.
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"Whenever I see an adult riding a bicycle, I know there is hope for mankind." (H. G. Wells)