If you are using a 16 ounce hammer put it back so you can find it to drive nails. To remove flywheels using the hammer method a 3 lb. hammer will work with a sharp smack but I like a 8 lb. sledge hammer squarely dropped from about a foot .
Flush the nut with the shaft end and use a nail bar etc. to just raise the shaft the thrust distance . Since we aren't trying to pry the flywheel off but are just lifting the shaft and flywheel, about 5 pounds pressure on the end of the bar is plenty .