Things You'll Need
The sprocket on a STIHL chainsaw is the toothed wheel located between the guide bar and the engine, which drives the saw chain. To maintain the service life of your saw chain, STIHL recommends that you replace the sprocket on your chainsaw after you have gone through two chains or sooner if the sprocket shows more than 0.5 mm of wear. STIHL advises alternating between the two saw chains to help keep the sprocket from wearing out prematurely.
Unscrew the sprocket cover nut and remove the cover. Turn the guide bar tension screw counterclockwise to release the chain tension, and then remove the chain and guide bar. Pull the hand guard against the handle to release the chain brake.
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Remove the E-clip from over the sprocket, along with the washer and rim sprocket. Remove the clutch drum and/or spur chain sprocket, followed by the needle cage underneath.
Clean and lubricate the crankshaft and needle cage. Put the needle cage back on the crankshaft.
Put the new clutch drum and/or spur chain sprocket on the crankshaft and turn for approximately one full turn until the carrier for the oil pump drive engages.
Put the rim sprocket back on and make sure that the cavities face out. Replace the washer and E-clip.