Adjusting the chain tension on your Stihl chainsaw is necessary to prevent damaging the chain and chain bar. It is a safe practice to check the chain tension before each use of the chainsaw. The chain tension weakens each time you use the chainsaw, causing slack in the chain. Adjusting the chain tension on a Stihl chainsaw is generally the same on all their models, though the tensioning screw might be in a different location.
Place the Stihl chainsaw on a level surface. Unplug the spark plug wire from the spark plug. Find the tensioning screw for your Stihl model. Some Stihl models have a tension screw on the front of the engine between the right side of the chain bar and engine. Other models have a tensioning screw visible between the two nuts holding the side cover onto the engine body.
Put on a pair of thick leather work gloves to protect your hands from the sharp edges of the chain. Loosen the two nuts securing the side cover with a wrench. It is only necessary to turn each nut two complete revolutions.
Grab the end of the chain bar with your fingers, and lift the chain bar until it stops. Do not lift the body of the chainsaw when lifting the chain bar.
Turn the tensioning screw clockwise with a flat-head screwdriver until the chain fits snugly over the bottom of the chain bar. Release the chain bar. Tighten the nuts securing the side cover.
Pinch the top of the chain at the top middle of the chain bar with your fingers. Pull the chain forward to ensure it rotates freely without binding. If it binds, loosen the tension slightly and recheck.