Any Chainsaw Guru's ?

[jimmy milnes]

Needing to pick the brains of any chainsaw mechanics please.
So yesterday I was cutting some logs and the saw just stopped dead.
Sthil ms391, initially I thought it'd overheated and nipped up even though it was oiled up to the correct proportions in the petrol.
Going to it this morning and I've pulled the plug and the piston moves freely without any horrible or unusual noise, however it will do a full revolution in either direction but won't pass top dead centre "just feels like a dead stop as if its hittingsomething", I've shook it to see if I'd popped a ring and that was locking it up but nothing rattling or anything, obviously 2t so no valves to hit and as it's tdc where it stops I'm imagining it's not snagging on a port..
I'm lost can anyone shed any light on it please?
Cheers
Jimmy.

 

[Gunner223]

Take the head of and have a good look inside,

 

[Outback]

Is the plug complete ?

 

[gixer1]

You can buy a handy endoscope off Amazon for £30 well worth it for jobs like this!

 

[jimmy milnes]

Is the plug complete ?

Yeah fully intact matey cheers. Maybe the decompress button I suppose but I've not removed that yet

 

[beatie]

have you checked the sprocket and clutch drum

 

[jimmy milnes]

have you checked the sprocket and clutch drum

No beatie thanks for the heads up, I'll have a look at popping that next weekend and see if it still locks up

 

[Outback]

We had a dump truck that wore out one half of a big end shell that then would turn each way and jam in the space against the other shell and the crank .

 

[jimmy milnes]

We had a dump truck that wore out one half of a big end shell that then would turn each way and jam in the space against the other shell and the crank .

Surely I'd feel or hear that as I turned it ?

 

[Outback]

As you turn the crank the piece like a shim moves into the gap between the remaining shell and the journal and jams , turn it back and it free's then jams the other way .

 

[Skogsmannen]

if you haven't alreadh, Whip exhaust off and take a look in from that end as you might be able to see a bit more.

I once encountered an old husky 181 that had lost the little steel pi n that stops the piston ring(s) spinning and that could give symtoms similar to yours if it 's embedded itself in a certain place.

either way it sounds like a cylinder off job, which isn't half as s cary as it mig ht sound

 

[Skogsmannen]

Usually if it's nipping up you'd get some warning before hand - almost like it's running out of fuel

 

[jimmy milnes]

It's official.....
Saws deed,
Hole in piston..
Bits too expensive to make it viable..
Thanks to all who gave advice.
Jimmy

 

[jimmer.13]

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Not to difficult and worth having a bash mate. Plenty of tutorials on YouTube

 

[Skogsmannen]

a non-gen top end would definitely be worth doing but you'd need to work out why it went pop in the first place.

Out of curiosity, hve you a photo of the damage?

 

[countrryboy]

Id echo wot skogs says above or price parts yp on L&S engineers.

Nowadays with saws quite often old is gold, be better than most of the saws ur likely to buy to replace it.
But be worth knowing wot caused it before u spend too much on it.

 

[jimmy milnes]

a non-gen top end would definitely be worth doing but you'd need to work out why it went pop in the first place.

Out of curiosity, hve you a photo of the damage?

Took as good as I could through the exhaust port

 

[foxinmad]

Pull the heed off it matey and have a gander

 

[dropmdead]

I'm not a chainsaw expert but I have an Idea about two strokes.
You can tell (pre)detonation, wrong mixture, dirty getting in etc.
The phrase "they just don't make them like they used to" doesn't occur from nowhere...

Give it a thorough clean and then strip it down and see where it's at. It's a Stihl and it's sold on quality, so replace with a rebuild kit.

As a side note from my two stroke days, it does no harm to inspect the ports in the cylinder for a miniscule chamfer to help with ring engagement and not being snapped. Also, a couple of heat cycles help with the running in..I know - you don't run them in but.

 

[nic531]

If you decide that fixing it is not for you, either sell it on the bay of thieves or if you were local I would happily take it and give it a go at fixing it..... one can never have too many chainsaws when you have no central heating just a woodburner