Sorry about that. I had a man in the shop last summer that though his electric PTO clutch screwed off like his chainsaw did. You need an impact gun. That will knock it loose before the engine has a chance to turn. You can try taking the blower housing off and locking now the flywheel. Now there is an old shade tree trick that can be used to lock the engine down. First remove the spark plug and then turn the engine over until the piston is at the bottom. Then take about 5 feet of small rope like the type used for pull cords. Tie a knot in the every end of it, there is a reason for the knot. Then poke the cord in to the spark plug hole until you can not get any more in but remember to leave some to pull it back out by. then turn the bolt you are trying to remove. When the piston comes up to top it jams against the cord and you can remove the bolt. When done remove the cord and look for the knot at the end. When you see the knot you know that all of the cord is out. On 4 cycles the knot is not that necessary but when the cord trick is used on 2 cycles it can get cut in to on the ports and the knot tells you if it is all there or not. The cord trick is an old trick you will not find in any book but it does work and it gives you some to to use when all esle fails. Good luck.
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