The sprocket on most McCulloch chainsaws comes attached to the clutch drum as one piece. This sprocket's function is to guide the chain along the bar. Due to the high stress and friction on the sprocket, you will need to replace it after it is worn, grooved or chipped in any manner. If the sprocket sits below the clutch assembly, which it does on most McCulloch chainsaws, you must remove the clutch to access the sprocket. There are some McCulloch models on which the sprocket is located above the clutch.
Things You'll Need
Piston stop tool
Clutch removal tool
Be sure the chainsaw is shut off. Use your fingers to pry off the high-tension lead wire plug that is connected to the spark plug. Detach the spark plug from the engine using the socket wrench.
Place the wrench over the bar nuts and unscrew them counterclockwise. Pry off the clutch cover, pull up the tip of the bar and slide the bar and chain back to disconnect them from the sprocket. Remove the bar and chain.
Insert the rubber piston stop tool into the hole where the spark plug was. Turn the clutch with your hand until it stops spinning after contacting the stop tool. Set the clutch removal tool onto the clutch hub. Attach the wrench to the removal tool and turn the wrench clockwise to free it.
Slide the clutch's washer, dust plate and assembly off the crankshaft stub; underneath is the drive sprocket and clutch drum. If your McCulloch's sprocket is above the clutch, skip the clutch removal steps.
Free the clutch drum and sprocket from the crankshaft stub. Pull the needle bearing out of the center of the clutch drum. Replace the sprocket and clutch drum. Spread a fingertip of engine grease along the inner and outer areas of the needle bearing. Push the needle bearing into the new clutch drum/sprocket.
Push the needle bearing and clutch drum/sprocket down onto the crankshaft and then place the clutch assembly over them. Put down the dust plate and washer. Refit the removal tool and wrench and tighten the clutch hub counterclockwise. Take the stop tool out of the spark plug and reattach the spark plug. Reconnect the bar and chain to the drive sprocket, and put the clutch cover in place.