I posted this over on Arbtalk, but thought it might be worth trying here too.

I was using the strimmer today and it very briefly started to vibrate then the head stopped revolving and the revs went up.

I thought immediately that the gearbox had gone at the head. I removed it and it seems to be fine. I also pulled out the long drive shaft and it too seems to be in tact.

When I revolve it inside the long housing there is no resistance at the engine suggesting that clutch has broken. Is this a fair assessment?

I set to removing the cowling at the engine along with the carb. I pulled the four screws which hold the plastic / rubber vibration mounting from the engine, but I can’t seem to split it.

Two questions. Am I along the right lines with the clutch diagnosis? How do I spit the shaft / housing from the engine.

Three questions, a bit like the Spanish inquisitors

Will I need any special tools to remove and refit the clutch?

[video]http://youtu.be/vt0Y39eMvpI[/video]

But I’d be off to a Stihl dealer to have it fixed I think. Will cost less than you expect.

This any use?

http://www.motoculture-jean.fr/upload/pdf/FS400_FS450_FS480.pdf

But I’d be off to a Stihl dealer to have it fixed I think. Will cost less than you expect.

Where is the job satisfaction in that?

I managed to disconnect the lower portion of the cowl to be left with just the ‘bell housing’ left still attatched to the engine. Geoff’s PDF showed a bearing mounted into the bell housing retained by a circlip. I removed the circlip but can’t see a way to pull the bell housing clear to reveal the clutch.

Any suggestions from the evening crowd?

Flog it for spares and buy an Echo; enjoy a new fresh world of professional brushcutting.

If you get to the point of removing the clutch from the crank you will need a dummy spark plug to lock the crank – like a long plug which stops the crank turning over so you can unscrew the clutch unit.

If you get to the point of removing the clutch from the crank you will need a dummy spark plug to lock the crank – like a long plug which stops the crank turning over so you can unscrew the clutch unit.

I might have one among my chainsaw tools.

I just remove spark plug & stuff some blue plastic rope into chamber,turn motor over till it locks undo clutch housing ,sort then after tightening up new clutch or what ever pull out rope 🙂 simples

Just bear in mind the clutch could well have a left hand thread.

Saying that, looking at the pdf you shouldn’t need to remove it unless you have to replace the springs. If the springs have gone they tend to drag the clutch at low revs which can make them hard to start and obviously the clutch may not disengage during idle.

Current thinking is the drive shaft may have slipped out of the output square drive due to a loose clamp screw. Clutch might be ok, will test in the morning.

The clutch should only engage when the engine is running, so there should be no resistance in the shaft or head anyway. If the clutch is broken the head will revolve when you pull the starter cord. As you currently think, there is a missing link in the drive train.

Yay! The clutch was ok, it was just the driveshaft that had slipped out. The bonus of taking something apart is that I now know how it works.