Best method I have for removing that bolt is to remove the crank pulley and belt. Then thread two bolts back into the dampener adjacent (next to) each other. Place a breaker bar in through those bolts so that it can't turn CCW. Now back the nut off. If it's so tight that you can't hold the breaker bar with enough force, put a really long one in there so that it wedges against the ground.
FWIW, I'm not brave enough to try bumping the motor over to loosen it (and I think it's a bad idea to try), but if you do, remove the coil wire at least so there's no way it can accidently start.
