Before we get into it I need to post this pic of Al.
Back to our broken saw. The customer wanted to remove the clutch and do some repairs on the oil pump. To remove the clutch you need to prevent the engine from turning over so you can unscrew the clutch from the crankshaft. A popular way of locking the engine is with a piston stop. This could be a special tool, a stopper that replaces the spark plug or even a piece of rope pushed into the cylinder through the spark plug hole.
Our guy tried something else. There was a note on the repair card about the customer using a skrench (that tool you get with some equipment that is a screwdriver and a spark plug socket in one) to hold the piston. At first I didn't realize what was being said but then it was pointed out that he admitted to putting the screwdriver into the spark plug hole, across the top of the piston and into the exhaust port. I'll try to explain better with this pic.
Here you can see where the screwdriver crossed the top of the piston. The burr created from the screwdriver jammed in the port and the pressure applied when removing the clutch created a raised edge and then this scoring. Now the piston ring is seized in the groove and can't seal very well to the cylinder. The engine only develops 90 psi compression and that's not enough for the engine to run.
This saw will get a new piston and cylinder. A costly mistake that you will never make.