bwdbrn1· Super Moderator
Welcome to the forum kents99. Try taking the spark plug out and stuff a length of rope into the cylinder. As you turn the nut, the rope will compress in the cylinder against the top of the piston acting as a stop, and keeps the pto shaft from turning. You might try an impact on the nut too. I have one of these in my tool box, and use it fairly often. It's pretty inexpensive, and gets the job done. For those not familiar with this sort of impact wrench, you twist it in the direction you want to apply force, in this case to loosen, and strike the end of the impact with a hammer. It may take several blows to loosen the nut.