How do I remove the bottom bolt to replace the PTO. The crankshaft keeps rotating with the bolt. Is there a special tool to keep the shaft from moving.

You can buy a piston stop that screws in the spark plug hole , or if you have access to a impact gun.
Luck

Hi,
A cheaper way is remove the spark plug and insert a doubled length of rope. Acts like a piston stop and causes no damage.
I prefer those air tools myself.
Peace,
Clarke