Stator Rotor spinning on the crank

I cant keep the rotor from spinning on the shaft when I crank the starter. I had a problem long ago where the rotor came loose and now it wont stay tight to the crankshaft. I dont know how the rotor stays in place without a key of some sort, even being conicle; which makes it a lot harder to broach and key. Anyone got any backyard solution to this problem? Overtorque? retap with reverse threads? I really want to avoid pulling the motor apart to machine it. Has anyone else had this problem?

1978 KZ1000 mostly stock aside from pistons, cams, ignition, fuel system, etc.

It's a taper fit, and it sounds like the taper is messed up.

Shadetree/backyard/cheap fix is to use Loctite stud and bearing mount on the shaft, worked for me anyway