The sprocket on most McCulloch chainsaws comes in a part that's combined with the clutch drum. So when you replace the sprocket, you will need to replace the clutch drum as well. The sprocket and clutch drum can get worn out over time or if you use old or worn out chains. Conversely, you can tell when your sprocket is worn out when it wears out new chains quickly because the chain's guides run over the sprocket when it's spinning. This wears down the guides.
Disconnect the spark plug wire and boot from the end of the spark plug, which is located at the bottom of the cylinder case on a McCulloch. Overlay the socket wrench onto the spark plug and loosen its holder. Pull the spark plug out and remove the socket wrench.
Set the chainsaw with the guide bar and chain pointing up. Use the wrench to loosen the two retaining nuts holding the clutch cover in place. Take the clutch cover off with your fingers. Dislodge the bar and chain from their seat on the sprocket and remove them.
Stick the rubber piston stop tool into the now empty spark plug hole. Turn the clutch by hand so that the piston contacts the stop tool and no longer spins the clutch.
Unscrew the clutch nut with the wrench by turning it clockwise, since McCulloch clutches use a reverse thread for their nut. Take the clutch nut off. Insert the tip of the screwdriver underneath the corner of the dust plate. Pry the dust plate loose and remove it.
Pull the clutch assembly off of the crankshaft, underneath the clutch assembly is the clutch drum and sprocket. Remove the clutch drum and sprocket; also remove the bearing and washer underneath the clutch drum.
Apply about a fingertip worth of engine grease to the bearing. Spread the grease along the inner and outer walls of the bearing. Set the washer and bearing back onto the crankshaft.
Place the new sprocket and clutch drum on top of the bearing. Set the clutch assembly back in place. Secure the dust cover by pushing it onto the clutch assembly. Screw the clutch nut back down by turning it counterclockwise with the wrench.
Remove the piston stop tool; set the bar and chain back onto the sprocket. Install the clutch cover, spark plug and rubber boot.
Remember to grease the bearing every time you remove the sprocket.