Griesel, I have refined the post. It never occured to me that someone would try rolling the engine with the starter with the chain off.
The head will only loosen. Not lift off the engine exactly. First I would try the hitting the head with the head under tension. If that failed then the compressed air making sure the cylinder used was at the bottom of its bore. A lot of times a person has missed a fastener when trying to get something apart. One has to be positive they are all acounted for before using real force.