no way are you going to be torquing it to double, thats either going to stretch and yield the bolt best case, or pull the crank thread out (thats bad)
I agree the intial issue is likely caused by not having crank bolt tight enough. Plenty of engines dont have key on the crankshaft at all.
if it was me, and I didnt want to do it properly I would lean in on the dodginess and loctite the balancer on. Then in the future hate myself but thats future Ben's problem.