The chain tensioner is a short threaded screw that runs parallel to the blade or bar of the chainsaw and makes it possible to tighten the tension on the chain as it loosens over time. The construction of a chainsaw chain allows the chain to flex, which causes it to stretch over time, requiring periodic adjustment to allow for the best cut. The tensioner is located inside the bar cover in front of the chain sprocket. It is simple to access and can be replaced in a few minutes.
Turn the saw off, and pull the spark plug wire boot free from the spark plug to prevent accidental starting. Lay the saw on a sturdy surface with the bar side up.
Use a socket wrench to loosen and remove the bar cover bolts. There are two bolts at the front of the cover, where the bar enters into the housing. Turn them counterclockwise to remove. Lift the cover from the saw to expose the blade tensioner screw assembly.
Use the combination wrench that came with your saw to turn the screw counterclockwise to loosen the bar. Shift the bar toward the back of the saw and remove the chain and bar. Locate the chain tensioner, which is a flat metal plate under the tensioner screw. Use a screwdriver to remove the two screws holding it in place, and lift from the motor housing.
Position the new tensioner, and insert the mounting screws. Tighten them with a screwdriver. Replace the tensioner screw and thread it in lightly, just one or two turns. Replace the bar over the bar bolts, and fit the chain over the sprocket and the end of the bar. Slide the blade toward the front of the saw to snug the chain up.
Replace the bar cover and tighten the bar nuts finger tight. Turn the tensioner screw clockwise to tighten the chain as much as desired. Consult your owner's manual for more specifics on tensioning for your model. Tighten the bar nuts with the socket wrench to complete the repair.