Stihl FS450 strimmer 'clutch' problem?

[mcmoonter]

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?

 

Thanks Peter

[doobin]

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?

 

No, you won't feel resistance as it's a centrifugal clutch

 

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? They don't usually just let go like that. I'd take it all apart, check the clutch looks OK (ie. not in three bits) and re-assemble, making sure that the outer shaft is correctly located. Most likely this has come loose, meaning the inner driveshaft is not correctly seated. A manufacturing error leading to cracks in the clutch housing means that this is a common problem in the later FS460s

 

How do I spit the shaft / housing from the engine.

Just undo the two clamps that hold the anti vibe bit on and remove the outer shaft. The anti vibe bit just presses in to the engine on rubber mounts.

Three questions, a bit like the Spanish inquisitors

 

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

 

Thanks Peter

 

 

Hope this helps.

[mcmoonter]

Thanks Doobin.

 

I managed to disconnect the lower portion of the cowl to be left with just the 'bell housing' left still attatched to the engine. I found a PDF which 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.

 

Is there anything you can suggest?

[doobin]

Sstick the outer shaft into the clutch housing (all the way), and then insert the inner shaft. You can leave the antivibe and handlebars off for now. Ideally clamp the shaft in a vice with the head end pointing slightly up, then start the engine. If the shaft turns when you rev it, turn it off, stick the gearhead on and test it again under load.

 

I'd do all that (about 5 mins work) before messing around with the clutch.

[mcmoonter]

The square drives in both he gear head and the visible portion into the bell housing look to be in tact. The inner shaft faces looked to be good at both ends too. Before I stripped it, there was no drive to the gear head at all, the engine just revved like it was in neutral.

 

I will give it a running bench test with the inner shaft visible in the morning.

[doobin]

The square drives in both he gear head and the visible portion into the bell housing look to be in tact. The inner shaft faces looked to be good at both ends too. Before I stripped it, there was no drive to the gear head at all, the engine just revved like it was in neutral.

 

This can happen if the clamp holding the outer shaft to the clutch housing becomes loose- it simply means the inner shaft will not be engaging properly with the output female shaft. You won't notice it's loose as the anti vibe will stop the outer shaft from rotating and mask the extra half inch of length.

[mcmoonter]

Genius. So the drive shaft just slips out. That would save a lot of bother. The machine has never given any indication of clutch wear, so you may well be on to something. I will report back.

[doobin]

Genius. So the drive shaft just slips out. That would save a lot of bother. The machine has never given any indication of clutch wear, so you may well be on to something. I will report back.

 

I did try to explain all this in my first post

 

Hope it works out to be that.

[mcmoonter]

I reassembled everything, ensuring the shaft was properly located and the bolts clamping the to the shaft were tight and it works!

 

Thanks for your help on this.

[doobin]