Bicycle crank cotter pins are stubborn things. There's a sure-fire way to remove them that does not involve a hammer,[1] but it does require a small mechanic's vise like this one.
That's a 3" vise. That size is big enough to do the job, but small enough that it can be manipulated as a 'hand tool'. I can't recall what I paid for it, but it was on special at Canadian Tire and wasn't expensive. (I've removed the vise's swivel base to lighten it a bit.) Make certain that the vise's screw and screw-head thrust-face are well lubricated.
Cotter Pin Preparation
Loosen the cotter pin's nut, and back it off to where its outer face is just past the end of the threaded stud, like so.
At the head end of the cotter pin, place a 3/8" (9/16" A/F) hex nut that's been bored out to fit over the cotter pin's end (3/8" diameter typically). The nut must be taller than the height of the cotter pin's protruding end.
Now, take the vise and clamp its jaws squarely onto the prepared cotter pin.
You'll need a big adjustable wrench for leverage on the vise.
Now crank on the vise's screw for all you're worth. (You may need to add a suitable length of pipe to the vise's handle for increased leverage.)
Eventually, there'll be a big "POP", and the cotter pin will be free.
* * *
CAUTION
When the pin 'pops', the vise may suddenly fall away. Be clear of its path. Wear eye protection. The force involved in this procedure is huge. Unforeseen stuff can happen.
* * *
And there we are -- the cotter pin is out, and not a single hammer blow was struck.
I can't say that I've done this procedure often, but it has yet to fail me.
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Note:
[1] Hammering setups like the one pictured below are hogwash.
The wooden 'anvil' will absorb much of a hammer blow's force. What's pictured is a recipe for damage and frustration -- it's not a reliable method for removing cotter pins.
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