ski-doo 583

my buddy put a 89 583 motor in a 85 plus but has crank thread problems.HE said 89 583's had different taper but all tapers since late 70's are 30mm right? he said 1st clutch he put on had wrong taper and shook.2nd clutch he put on using all-thread to hold it.it tossed the clutch(of course) NOW i have to fix it but all bolts i've tried strip.I retapped crank but it just feels so sloppy,the threads look great and I know the crank is hardened(1/2-20 is what i come up with) HELP!! is it screwed? stan

ski-doo 583