Did you strip the hole in the crank that retains the balancer or a hole in the balancer that retains the crank pulley? I didn't get a clear image of what you are working with.
If the crank, you might have just pulled the first couple of threads, clean it up (if you can find a tap that size or buy another bolt and use that as a tap) as 67 427 said. If you tried to "pull" the balancer on the crank with the bolt, that's probably what happened. If it is worse, find someone with experience with helicoils to help out. Finding a drill bit, tap or helicoil kit to fit a 3/4" or whatever size thread that is may be a challenge, also having a drill to run that bit at the right speed may be tough as well.
If you stripped one of the bolt holes in the balancer, I would just drill and tap to the next size thread 3/8-16 or whatever.