What is a Chainsaw Sprocket?

The chain sprocket is the driving force behind the chain (this is hidden behind the sprocket cover). Made from wear-resistant steel, this transmits the power from the engine to the chain loop. The chain sprocket teeth then press against the link tanks and the saw rotates. Drive sprockets must always match the saw “pitch” which is being used, this information is normally stamped onto the sprocket.

Sprocket Types:

Spur

A spur chain sprocket is a standard part that is soldered to the clutch drum and usually displays a star shape. A spur sprocket normally has between 6 and 8 teeth. The drive links sit in between the teeth, which drives the chain.

Rim

A rim sprocket is arranged on the clutch drum hub. The chain links are inserted into the rim, which drives the chain. A rim sprocket usually has 6 and 8 points, and when the rim is worn (usually 0.02mm) this can be easily replaced with another rim in comparison to changing the whole sprocket.

(Keep in mind this will be dependent on the machine you have and if they are able to take both types)

What can happen when the Sprocket is worn?

The sprocket is meant to be changed after 2 - 3 chains, so if you continue to use a worn sprocket this will damage the drive links and consequently widen the bar groove reducing cutting performance. This can lead to additional problems with other parts, making a small job into a costly repair.

Stihl recommends checking the condition of the chain sprocket regularly using a control gauge. If the depth of the wear marks reaches about 0.5mm i.e. the wear limit, the chain sprocket must be replaced.

Stihl Wear Control Gauage - 0000 893 4101»

Why are there different amounts of teeth on sprockets?

Changing the number of teeth on your chainsaw’s drive sprocket to change the performance is called gearing. This is done on both spur and rim sprockets, although it’s easier on a rim sprocket due to their functionality. It’s best to stick with the drive sprocket tooth count that came on your chainsaw from the factory.

Spur Sprocket

Rim Sprocket

Gearing Examples:

• More speed will mean a jump in tooth count.
• More strength will mean a lower tooth count.

Both will need factors addressing such as chain gauge and bar length.

(Best tip is to look after your chainsaw and follow the recommended advice from your manufacturer.)

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