Drive Sprocket Info:
An important part of the cutting team on your saw is the drive sprocket. Whether a spur or Powermate sprocket system, there are some things you can do to maximize cutting performance and longer product life.
If you are the type of woodcutter who uses one chain until it's gone and then buys one more, we recommend a new sprocket with every chain. A new chain on a worn sprocket is guaranteed to stretch out of pitch after a few trips around the bar.
If you use more than one chain at a time, then you can use the one-sprocket-for-two-chains process: when you buy two new chains, buy a new sprocket as well. Alternate the chains on the sprocket so both loops wear out at the same time. Then, it's time to go get two new chains and another new sprocket. This procedure saves you money on sprockets and keeps the chains in good shape as well. (Don't forget about the guide bar, too; these same comments apply).
When you change your chain and have the saw opened up, have a look at the sprocket drum. If you see any cracks or missing pieces, it's time for a new drum. At full throttle, the expanding clutch puts tremendous force on the drum, and a failure could be catastrophic.
All sprocket drums have some kind of bearing or bushing. The bearing has to work only at idle, because at full throttle the drum is turning at the same speed as the crankshaft, but if your saw is like most, it spends a good part of its time idling. If the bearing isn't working, the chain may be in motion while the saw is at idle, and this is a safety issue. So, the point is, that bearing or bushing needs a shot of grease periodically; the grease you use for your sprocket-nose bar will do fine.
On the sprocket itself, check for wear. We recommend replacement when the diameter is reduced by .020" or more. That means .010" indentation on each tooth of a spur or rail of a rim. A human hair is about .003", so you've got three hair's worth before it's time for a new sprocket.
A drive sprocket is a lot like the transmission on your car; it's not as exciting as the engine, and not as appealing as the finish, but without it, the car won't go. Check your sprocket often to make sure an important saw component doesn't let you down when you need it most.