The chain tensioner on a Husqvarna chainsaw controls how tight the chain is against the bar. Proper chain tension is needed to cut efficiently and safely. Without the correct chain tension your chain may get thrown easily from the bar, break or get pinched easily. Replacing the chain tensioner is necessary if the screw no longer holds the chain tight against the bar when cutting. Installing a new chain tensioner on your Husqvarna 351 isn't difficult and only requires about a half an hour of time to fix.
Things You'll Need
Leather work gloves
Chain tensioner kit
Turn off the saw and release the chain brake. The chain brake is the plastic handle located on the topside of the saw's body, and is in between the bar and the throttle. With a gloved hand, spin the chain to ensure the chain brake is off.
Use the wrench to loosen the bar nuts until they are finger tight. Use the flathead screwdriver to loosen the bar tensioner screw. This screw is located just beside the bar cover's two metal posts, and can be reached through the small, round hole in the cover's center. The tensioner screw controls the chain's tightness.
Finish loosening the bar nuts and remove the bar cover. Take off the bar and chain; set them aside in a safe place.
Find the chain tensioner apparatus. This will be a flat metal piece located directly underneath the chain tensioner screw, which you removed in the earlier step by taking off the chain's bar cover. It will be in between the clutch housing at the rear and the chain's catchguard in the front.
Use the screwdriver to unscrew the two screws that hold the chain tensioner's cover in place.
Remove the outer plate and you will see a long bolt running in the same direction as the chainsaw's bar, which is connected to another piece that looks like a handgun. This is the chain adjuster tensioner apparatus.
Unscrew these two parts and remove them from the engine housing. Look at the inner plate behind these two parts. If it is cracked or damaged, remove that as well.
Replace the necessary parts from the new chain tensioner kit. Screw them back into the same place you found them. Replace the tensioner screw as well. Most likely this will solve your adjusting problems. If not, it is likely your clutch assembly or sprocket that needs to be replaced.