Using a screwdriver, remove the cover that hides the flywheel sprocket located on the chain saw housing. This not only exposes the sprocket, it exposes the two bolts that hold the chain saw bar onto the chain saw motor.
Remove the chain from the sprocket and inspect it for any noticeable defects such as a broken chain link or for bends that keep the chain from resting flat on a tabletop. If you notice defects, purchase a replacement chain.
Remove the two bolts that secure the chain saw bar to the chain saw motor with a wrench. Place the bar flat on a table and inspect it for bends. If bent, purchase a replacement chain saw bar. If the chain saw bar is straight, clean the groove around the perimeter of the bar with a wire brush to remove any debris.
Place the chain saw bar back onto the chain saw motor and then tighten the bolts as tight as you can with your fingers. Slide the bar as far back toward the motor as possible.
Place the chain on the sprocket and then place the chain around the chain saw bar. The edge of the chain rests in the groove on the perimeter of the bar.
Pull the bar out away from the motor to create tension on the chain and then tighten the two bolts as tight as possible with the wrench.
Reinstall the cover over the sprocket.