Pour Hydrogen Peroxide in eack CYL and let sit over night. I have used this on many seized engines and it worked every time I used the peroxide. Get the small bottles and pour 1/2 bottle in each cyl. When trying to turn the eng by the damper bolt or flywheel, do it in a back and forth motion a little at a time. Don't try to keep turning the eng the same way. Back and forth little by little.
