Heat has always worked for me, most come off with the puller and a few encouraging whacks from the hammer but on occasion when necessary I have heated the outer rim of a flywheel with my B tank, when it would melt a 500 F crayon that was a good stopping point, wait a sec or two and hear that ,pop, puller pre tightened up to at least 50 lbs torque. I have not tried an electric heat gun as I doubt it could get the flywheel hot enough, maybe it could but a flywheel will lose heat rapidly due to all the fins on it so I find it needs a hot concentrated heating device.