I built and sold Sachs conversions for a few years and "straightened" several cranks from engines that had suffered those sudden stops caused by contact with terra firma. Cranks don't actually bend but do in fact twist the counterweights on the crankpin caused by the front half of the crank stopping while the back half continues on for a very short distance. This means the front shaft and back shaft are now rotating on two different centers. A press is definitely not the way to fix a crank. A lathe, vice, big hammer and lots of patience is required and it's best to send it back to the engine builder. I've seen many cranks made "perfect" with a press go right back out when reinstalled in the crankcase.