As a 40+ year chain saw user I must say that in the first place never run a chainsaw with a loose chain. The chain can jump off of the bar, go whipping around, and cause serious personal injury or death. I've always been VERY careful about this, and yet, two years ago I negligently ran a saw without first checking the chain slack. The chain jumped the bar track, and almost cut my gut open. The chain runs with a LOT of torque and, usually, speed. You need to check the slack each time you use the saw. It often needs adjustment. If you don't know how to properly and safely remove links, have a professional do it, or get a new, shorter chain. And always check and adjust for slack before using the saw. A chain saw is one of the most dangerous pieces of equipment that a person can use. MANY things can go wrong if you are not properly trained in its use. No one should operate one without training by someone who really knows how to use one and teach others to use one. Also, constantly check the groove all the way around the bar (that the chain runs in). It can get clogged up with sawdust to the point that the chain does not seat all the way down in the track and will jump off of the track.
