From FBinNY, multiple previous posts:
It's childlishly easy to remove a crank with a stripped puller thread.
There's the free way that works about half the time. Replace the spindle bolt, but leave it backed off about 1mm. Ride the bike up a steep embankment in a high gear so you really have to stand on the pedal. If you hear a "crack" the crank has popped free, so stop riding immediately, and you're good to go after walking back to the shop.
Or for a few bucks at a good commercial hardware store you can buy a pair of Jacobs Chuck removal wedges.
(see picture) These are thin pieces with shallow tapers, and tapping the pair in from both sides will push a crank off while remaining parallel. Many shops have these, and will do the job for a nominal fee.
BTW- Chuck wedges work so well, that there's no reason not to continue using the crank arm.
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