Drive Sprocket (Part 2)...

In the previous post we looked at removal of the drive sprocket from a Stihl chainsaw, which uses an inboard clutch (which makes removal very simple).

In this post we'll take a look at the slightly more awkward procedure when dealing with machines fitted with an outboard clutch - in this example we'll be using my Husqvarna 350 chainsaw. Find out more, and watch the video, after the jump...

Those chainsaws that use an outboard clutch need to be tackled differently from those fitted with an inboard clutch. Husqvarna, Partner and the Stihl climbing saws all utilise outboard clutches.

The issue with these machines is that the clutch actually prevents you from removing the drive sprocket, and attempting to undo the clutch weights just turns the engine over (let alone the fact that it's threaded the 'wrong' way).

So, remove the drive sprocket from these machines is a bit more involved; here are the steps:

1. Remove the side plate, bar and chain.


2. Remove the engine cover to gain access to the spark plug.


3. Remove the spark plug and fit in a piston stop tool.


4. Knock the clutch weights off (remembering the thread is reversed).


5. With the weights off, the drive sprocket can be removed along with the roller bearing.

The following video, although based on the Husqvarna 350 chainsaw, should be relevant to all chainsaws fitted with an outboard clutch.

Replacing Stihl's Drive Sprocket

I thought I should even up the scores a bit - after doing a short video on taking out a Husqvarna drive sprocket, I thought I should create one for Stihl saws (although due to my own ineptitude you'll see the Husqvarna video in the next post). Watch the video after the jump...

As I mentioned in an earlier post, removal of the drive sprocket from a Stihl ground saw (or indeed most ground saws with an inboard clutch), is particularly easy; and that makes for easier maintenance. So the following video, based on a Stihl MS260, should be relevant for most saws having the same clutch setup. It's about 3mins 30sec long and represents my most advanced video to date! (Although the YouTube quality leaves a little to be desired - I just wish I could show the full MPEG-2 video CD.

Clutches...

The clutch on a chainsaw is of a centrifugal type, so that as the engine spins the clutch weights move out and engage with the inside of the sprocket.

Although there is little maintenance to do to a clutch, read on after the jump to find out a little bit more about the different clutch types...

There are two basic clutch configurations in use:

• Inboard clutch.


• Outboard clutch.

The image to the right shows an example of an inboard clutch as used on Stihl machines, and by Poulan as well, I think - although that's a US-based make rather than UK (interestingly enough Poulan is owned by Husqvarna, who mainly use outboard clutches on their own machines!). This clutch configuration has one great advantage - it's extremely easy to remove / replace the sprocket should you need to.

Outboard clutches, as seen in the picture on the left, are commonly used in Husqvarna and Partner saws, and Stihl climbing saws. This type of clutch makes removal of the drive sprocket much more awkward, but assessing the state of the chain brake band is made much easier.

In the next few posts we'll take a look at the drive sprockets, before returning to check out the clutch weights.