Patent ID: 7600323

Claim:
A chain saw comprising an auto chain tensioner, the auto chain tensioner comprising: a guide bar for providing a tension or a relaxation to a saw chain running along the guide bar, a single chain cover fixing means for pressing and holding the guide bar between an engine case and a chain cover and for fixing the chain cover to the engine case, a slider piece which is disposed between the chain cover and the guide bar and slides linearly along back and forth moving direction of the guide bar, a tensioner which is slidable along a sliding direction of the slider piece, and a spring for connecting the slider piece and the tensioner, wherein the chain cover fixing means further includes a rotatable disk having a sliding mechanism for allowing one of the slider piece and the tensioner to slide along the back and forth moving direction of the guide bar, and the sliding mechanism forms a spiral guide groove on the disk, said spiral guide groove being engaged with a protrusion provided in one of the slider piece and tensioner, wherein the other one of the tensioner and the slider piece is engaged with the guide bar, and wherein said spring for connecting the slider piece and the tensioner is a coil spring, one end of the coil spring is fixed to the tensioner, and the other end of the coil spring is coupled to the guide bar with a screw portion coupled to the slider piece directly or via a screw portion attached to the end of the coil spring, said screw portion having a screw head accessible to allow external rotational operation, said screw portion moving axially with said slider piece upon rotation of said disk, and rotation of said screw head causing the other end of the coil spring to advance along said screw portion.