Jim,
What issue are you having? Have you damaged the threads of the nut?
To install, the taper must be impeccably clean and bone dry. We usually wipe the shaft and the bore with acetone or lacquer thinner. The key must of course be properly aligned. Then start the nut by hand, and a cordless impact gun should provide enough torque to seat the flywheel.
To pull the flywheel, unlock the nut a couple of threads with the cordless impact, then attach a harmonic balancer puller, and pop the flywheel. Then finally remove the nut and lift the flywheel off.
