bmp01

My money is on that. Either run on old pump grade fuel mix or the carb is gunked up. Lots to check, make sure you find something 'coz finding nothing is definitely the wrong answer.

I'm assuming the wire isn't a "design feature" but wrapped itself around the sprocket during a cutting incident. ... The chain running on being a result of the wire pressing on the crank and driving the sprocket (and chain) even when the clutch has disengaged. Happy to be told I'm wrong .... It'll all be fine in a bit though, the wire will soon wear to give running clearance and/or something else will break.

Giving the clutch a helping hand. ...

Oops.... Good inspection of chain required after that or is chain obviously fubarred? Was the "chain running on" the first sign of a problem ? No cutting issues up to then, no strange noises .....?... ???

Oh, ok, I'll go first. ... Other saw is a MS 192T and the box is cardboard like, crumpled news paper packing. And ermmmmm...... they need cleaning ? Nexxxttttt !!!

Here's another version, from a 021 parts list, L&S Engineers....

Private message sent to you regarding carb fix.

White smoke is usually associated with water (or coolant) going through the combustion chamber, not likely with an air cooled 2 stroke unless there is water in the fuel. But I'm guessing you changed the fuel for fresh mix when you did the fuel filter. ... I expect your white smoke is down to the 2 stroke oil you used during the rebuild, it's probably inside the exhaust and needs can good thrash to clean it out. That will have to wait. Have a look at this thread regarding carb problems : https://arbtalk.co.uk/forums/topic/111138-ms181-spluttering-and-bogging-down-at-high-revs/ HTH.

Piston is just as soft as the cylinder. So as Spud said if something has gone through the engine you'd expect to see a damaged piston too. So either piston has been replaced or it's a dodgy cylinder from the off. Could be aftermarket parts, do you know the saws history? Regarding assembly issues - the need to assemble the engine lose and bolt it all up in situe is a truely shite idea. I don't have any respect for Stihl for employing this design. Compound that with making it almost impossible to position the engine in the saw body.... just stupid. I've done a few now and it's not easy, best way I've found is to have the engine upside down and position the body over it. Well, the truth is you're not expected to rebuild these saws. Personally I'd just run it, you've changed and/or inspected all the bits that leak. If it's an old saw expect the carb to be a pain. ... bmp01

Replacement piston? Saw history. My punt - it's the roughness of the cast surface compared with smoothness of machined surfaces. Mr Rainford, is the squish band in the cylinder pitted ? (Squish band is the 2-3 mm wide ring around the periphery of the combustion camber).

Saws in bits already. ...

Right, that's a decent starting point. So this is the normal starting procdure (below), can you confirm at what stage your saw revved up "extremely high" ? This might help people to offer advice. 1) cold saw, so set to choke position, saw cranked, saw coughs at this stage, 2) control set to fast idle, saw cranked, saw starts and revs high (assuming chain brake not applied), 3) throttle trigger squeezed momentarily to disengage fast idle, saw should idle. Your air leak diagnosis could well be right, certainly if the saw revved madly while on choke (1 above). It'll be a big air leak in that case, inspect parts and replace as you are doing. The only example I can think of where this happened was with a MS181 where some of the screws - engIne to saw body came loose. These screws double up to hold the two halves of the crankcase together (clam shell engine) so the air leak was where you have the liquid gasket. There was a lot of grey paste from worn aluminium. ...

It's a bit difficult for peeps to comment on a problem when there's not much info to go on. What exactly was the problem that caused you to pull the saw apart ? I'd expect there to be an oil film inside the engine, especially if it wouldn't start and/or has been "cranked" lots with the choke on. It's typical of 2 stroke fuel to evaporate the petrol and leave the oil behind. .. Similarly, carbon on piston and combustion chamber is normal, within reason. And what is pitted? If it's the combustion chamber, after you've cleaned the carbon off - are we talking about the cast surface? That's normal. If the original piston and cylinder are genuine parts, they need to be wrecked before its worth looking at inferior aftermarket parts. Post some good pictures.

If you look from underneith, you'll see a slot at the operator end of the handle. The top cover has a clip with a barb on it which you can access in that slot. Flat blade screw driver in the slot to release the clip. Be super careful with the front end of the cover, there's a stupid flimsy piece of plastic ...

Put it back together with some Loctite, it'll be fine ? (...or not). I tried separating a knackered crank once (MS180) just for interest, tried all sorts of abuse, mostly involving hammers, couldn't shift it at all. You've been unlucky there. Vaguely remember some story about tuned 2 stroke bike engines being assembled and then welded to stop the crank becoming misaligned with use. Don't suppose you need too many degrees of rotation before the crank would seize on a multi cylinder.

But that wouldn't be truthful. ... I got loadsa 200T bits .... they is blinkin stuck together in one lump. Might be available for an elevated ebay price....?

Does anyone have. ... Or, Has anyone got. .... But not, "Does anyone got. ..." ??? bmp01

Threads in cylinder for the exhaust bolts look a bit suspect too, might need helicoiling... Same logic as above, fix it properly now or it will be unreliable just when you need it.

The carb on the 170 / 180 is completely different to the 171 / 181 / 211. The latter are strato engines and their carbs have 2 ports through them, 1 fuel and air, 2 air only...... (They already have Hi and Lo fuel screws).

Ditto, I really like the old school design and feel of this saw. I think I've now ironed out all the gremlins left behind by previous owners. ..

Carbs on these have an accelerator circuit that turns to sh1t on well used examples....

Bought a DSC6800i for 50 quid as a non runner, that needed a fuel line. Good condition saw too. Still haven't found a saw in a skip though.

...engine too small to drive the chain, buy a bigger, pro model saw....

So thats the whole point. .... Going to 8 tooth will increase chain speed by a multiple of 8/7 but it will reduce the torque by the same ratio. As is the way, you can't have something for nothing.

On an 8 tooth sprocket ?