Thousands of flywheels have successfully been removed as Jim just described. And many crankshaft threads have been damaged doing it. I suggest doing it another way.

Take two nuts, the same size as the shaft, and a short bolt same thread size. The shorter the bolt, the better. Try for about 1" long. Run one nut up on the bolt, start the other one on just a couple of turns, then run the first one back down against the 2nd and tighten them together. Screw the tool on the shaft hand tight, LIFT UPWARD on the flywheel, and give the tool a sharp rap with a hammer. Hit it squarely, so as not to bend it. You are actually driving the shaft out of the flywheel. If it doesn’t come, rap it again. It may take two or three hits, or more. A 12oz hammer is perfect. Put away that sledge and don’t bash it. It’s the shock that loosens the flywheel, not the bash. IT WILL COME OFF, without damage. Believe me, I’ve done it thousands of times, with the very tools shown below.

EDIT: What I just suggested is a redneck way of doing exactly what the special tools sold by Techumseh do. (second picture)

EDIT EDIT: Either tool, the secret is the force is applied to the end of the crankshaft, not on the threads.

screenshot on pc

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A proper tool is the best way but what I described works if there are enough threads engaged. The impact is spread. I have never damaged a crank just the top thread or 2 of the nut. I fix them with a proper size tap. I work on small motors only.