Chainsaw Repair

Well I still haven't had a chance to go over the saw. I got it almost for free because it wouldn't start and was making kind of a rattling sound when you pull it over. When I tried to check compression I took the spark plug out and the ground electrode was broke off the spark plug when I pulled it over it locked up. I think the ground electrode is stuck in a port between piston and port. Maybe a parts saw? Why would the ground electrode break off a spark plug unless it hit the piston? I will take it apart tonight.