When Should You Change a Drive Rim on a Stihl Chainsaw?

Guide Bar and Sprocket

• Guide bars and sprockets work together to keep the chain operational. The chain is driven around the bar by a drive sprocket, a wheel located between the bar and the engine with teeth sized to fit the tangs of the particular chain. The bar guides the chain while it cuts. Efficient and safe cutting depends on both the sprocket and the bar being in smooth operating condition. If the sprocket is worn, the rotation is affected, which puts stress on the bar and the chain's motion.

Rim Sprockets

• A Stihl chainsaw has one of two types of sprockets: a spur sprocket attached permanently to the clutch drum or a rim sprocket, which is mounted on the hub of the clutch drum. The rim sprocket enables the chain to run smoothly; but as a moving part, it's subject to wear and tear over time. Only the rim sprocket has to be replaced when the rim sprocket type of assembly wears down.

When To Change the Rim Sprocket

• The sprockets on Stihl chainsaws are made from wear-resistant precision steel, but the demands put on the bar and chain are great, and a worn sprocket reduces the life of the chain. Stihl recommends that the sprocket be changed after two chains have been used but sooner if the sprocket exhibits wear marks deeper than about 0.02-inch. Check for minute cracks on the sprocket as well. A gauge to check the depth of wear is available from Stihl dealerships.

Parts and Installation

• Stihl manufactures its own chains, bars and sprockets, and the rim sprocket should be replaced with another Stihl sprocket to ensure the chain runs correctly. Replacing the rim sprocket is not complicated and can be done with common household tools. Be careful, when removing and replacing the washer and E-clip that form part of the assembly, as they're small parts. The life of the rim sprocket can be extended by using two chains in rotation.