The flywheel key on a Husqvarna chainsaw connects the flywheel to the crankshaft. This small key, if damaged, will cause the flywheel to spin incorrectly and your engine to fire improperly. Damage can occur to the flywheel key if you hit a rock or other hard surface while cutting; it can also wear down over time. The flywheel is responsible for firing the spark at the right time, so if it’s not connected to the crankshaft you, will probably not be able to use your chainsaw.
Undo the four screws that fasten the starter cover to the engine with a screwdriver. Remove the cover, starter rope and pulley assembly.
Move the ignition switch to the “Off” position. Disconnect the blue lead wire that runs from the ignition switch to the ignition module using your fingers. Disconnect the ground wire from the ignition switch.
Disconnect the high-tension lead wire from the spark plug. Release the high-tension lead wire and the blue lead wire from their cable guide, which runs along the bottom, just below the flywheel. Remove the cable guide.
Unscrew the spark plug from the engine using the socket wrench. Take the spark plug out and insert the piston stop tool into the hole. Rotate the flywheel gently until the piston hits the stopping tool.
Unscrew the ignition module retaining screws or bolts with the screwdriver or wrench depending on model. Lift the ignition module out. Undo the two recoil starter pawls with the wrench and remove them.
Unthread the flywheel nut with the wrench until the bottom edge comes in line with the shaft’s outer end. Set the flywheel puller in place over the crankshaft and flywheel. Tighten the puller’s two outer bolts 10 turns. Hold the handle in your hand and tighten the center bolt until the flywheel comes out.
Take the flywheel puller, nut, washer and flywheel off the crankshaft. Pry loose the flywheel key from the crankshaft using the tip of the screwdriver. Replace the flywheel key.
Set the flywheel back in place over the crankshaft. Turn the flywheel until the key mates with the recess in the shaft. Put the washer and nut back in place. Use the flywheel puller to tighten the bolt to about 18.4 to 22.1 pounds per feet of torque.
Place the ignition module back into the engine but don’t tighten its screws. Turn the flywheel until the flywheel magnet lines up with the ignition module. Insert the feeler gauge in between the flywheel magnet and ignition module to make sure the air gap is set properly.
Take out the feeler gauge once the air gap is set to .3 mm and tighten the two screws to anchor the ignition module. Set the cable guide back in. Secure the high-tension lead wire to the engine. Take the stop tool out and reconnect the high-tension lead wire to the spark plug.
Set the blue lead wire into place under the cable guide and reconnect it to the ignition module. Attach the pawls to the recoil starter using the wrench. Reassemble the recoil starter and cylinder cover and put them back in place. Tighten down the cylinder cover and recoil starter with the screwdriver.