ok here's what happened....i was riding last year.....machine is a 1990 polaris indy 500 ..about 6000 miles.....machine quit . couldnt pull it over ....so towed it home...this summer i pull hear off and inspect juggs not scored and look factory condition so i spray wd4o let it sit and turn clutch till motor turns over...so i put head back on and it starts up fine...seems to run fine .....has anyone else ever had this problem...?.....looking for an explanation....

Sounds like it simply seized up. Piston got hot for some reason and expanded enough in the bore to lock up. Usually, the pistons should show some signs from this...

At that many miles, there's a good possibility that one of the crank bearings momentarily locked up. Probably the PTO side. If so, get the crank rebuilt ASAP before it spins the bearing outer race and destroys the crankcase, if it hasn't already. Do a crankshaft runnout check with a dial indicator before doing anything. Must be less than .004". The less, the better.