Use a knocker. You can buy one, or you can make your own for pennies. You need two nuts, same size as flywheel nut, plus a short bolt, same thread, and as short as possible. Screw one nut up on bolt, then second one on only a turn or two. Now run the first nut down against the second and jam them together. You just made yourself a special tool.
To use, screw the tool onto the shaft hand tight, pry upwardly moderately on the flywheel with a screwdriver, and give the knocker a whack on the end with a hammer. Put the sledge hammer away!!!! A 12 oz hammer is ideal. 16 oz at very most. It is the shock that does the job, not the bash.
DO NOT attempt this using only the flywheel nut!! That almost always damages the crankshaft threads. The knocker applies the shock to the end of the shaft, not to the threads.
This also works on lawn mowers and chainsaws.
