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pedrobedro
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Clean up your original cylinder and just fit a new piston. OEM cylinders are far better than any after market ones. The plating will be good when all the aluminium transfer is removed with some brick acid then rubbed down with some 240 grit aluminium oxide with WD40.
angellonewolf
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can you take it apart so we can see the scoring in the bore its self ?
8ob
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Aftermarket barrel/pistons are ok if you go for a decent brand like Meteor, they are every bit as good as Stihl https://www.ebay.co.uk/itm/METEOR-C...928105&hash=item5b50d33f09:g:IdIAAOSwPcVVxf37
The question here is why has it partially seized? Could have been the carb, dodgy fuel/oil mix,clagged up cooling or drawing air through crank seals. While its in bits it may be worth looking a bit further.
Bob
The question here is why has it partially seized? Could have been the carb, dodgy fuel/oil mix,clagged up cooling or drawing air through crank seals. While its in bits it may be worth looking a bit further.
Bob
At the moment, I'm running a test on a stihl MS392 I rebuilt to see how long it lasts. The Brother in law gave me one to fix for him, same symptoms as above, first thing I did was pop off the exhaust, bingo screwed barrel, piston & rings.... uneconomic repair for him with it with stihl parts, so he said keep it for spares (I have the same saw). For my business I was interested if these were a real option from OEM, so did a bit of digging and found the "chinesium" equivalent cylinder / piston kit for a quarter of the price. Now I have little faith and expect very little, but we'll give it a go.. only thing non chinese was the bearings, I use skf for that, better than stihl originals anyway.
First thing I noticed, out of the box the chinese cylinder the bearing journals on the cylinder looked like they'd been machined by chainsaw, rough as
... measured them up, and there was nearly half a mm of difference from the original. The crank bearings wouldn't even go in, never mind line up.. We're off to a poor start then, however I managed to dress the journals a wee bit and got round that, all built back up easily enough after that. Had a bit of hassle getting it to run right even though nothing had changed on the carb. Back to basics set it up / tuned it and ran it... ran it in fairly aggressively, and it now runs ok, the question is how long it will last.
Conclusion - is it worth it to use non OEM parts, yes and no. To date it's got about 3- 4 hours on it, so far no issues have raised their head (longest use in one hit was about half an hour). Plenty of compression, and starts well enough, so Yes, it runs right enough, however it's nowhere near as smooth, and seems to bog down more than my original MS392 but at a quarter of the price was it worthwhile for me as my own saw - yes, my time costs nothing, and if it spits the dummy after a few hours then so be it...
Could I afford to use the chinese parts on a customers saw, no way, for paying customers or if you want it to stay at the quality / longevity of Stihl, then stick to OEM.
First thing I noticed, out of the box the chinese cylinder the bearing journals on the cylinder looked like they'd been machined by chainsaw, rough as
... measured them up, and there was nearly half a mm of difference from the original. The crank bearings wouldn't even go in, never mind line up.. We're off to a poor start then, however I managed to dress the journals a wee bit and got round that, all built back up easily enough after that. Had a bit of hassle getting it to run right even though nothing had changed on the carb. Back to basics set it up / tuned it and ran it... ran it in fairly aggressively, and it now runs ok, the question is how long it will last.Conclusion - is it worth it to use non OEM parts, yes and no. To date it's got about 3- 4 hours on it, so far no issues have raised their head (longest use in one hit was about half an hour). Plenty of compression, and starts well enough, so Yes, it runs right enough, however it's nowhere near as smooth, and seems to bog down more than my original MS392 but at a quarter of the price was it worthwhile for me as my own saw - yes, my time costs nothing, and if it spits the dummy after a few hours then so be it...
Could I afford to use the chinese parts on a customers saw, no way, for paying customers or if you want it to stay at the quality / longevity of Stihl, then stick to OEM.
dobbslc
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That's well knackered! The compression you can feel is probably the seizure making it stiff to turn over. Take it apart and see if the barrel will clean up with some acid (I used to do it with the race bikes but cant remember the name of the stuff)
It might clean up well and then you can use a bit of fine emery cloth to take the glaze off.
As people have said above its worth checking everything as it seized for a reason!
Crank seals pulling in air, leaking gasket, blocked air filter making it run lean. You mentioned a 20/1 mix, too much oil can make the mix lean and cause trouble, I run my Husqvarna on Castrol 747 at 40/1 and it seems fine. Husqvarna recommends more oil if its not their own brand but that's just **** covering! Any good quality oil should be fine. 20/1 is "smoky" !
It might clean up well and then you can use a bit of fine emery cloth to take the glaze off.
As people have said above its worth checking everything as it seized for a reason!
Crank seals pulling in air, leaking gasket, blocked air filter making it run lean. You mentioned a 20/1 mix, too much oil can make the mix lean and cause trouble, I run my Husqvarna on Castrol 747 at 40/1 and it seems fine. Husqvarna recommends more oil if its not their own brand but that's just **** covering! Any good quality oil should be fine. 20/1 is "smoky" !
The_Yellow_Ardvark
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I wonder what the bottom end is like?
I have a friend ( must go see him again soon) near Hastings, a Tree surgeon and Gardener, he was having mixing issues.
What we did is a over kill, but it saved his machines and thus cost.
We set up a 20 litre fuel can and marked it with what machine and what mix.
So he has 4 cans, Husky, Skill and cheepo and unmixed.
The fuel is mixed in the correct ratio in the calm of home. Saved so much trouble.
I have a friend ( must go see him again soon) near Hastings, a Tree surgeon and Gardener, he was having mixing issues.
What we did is a over kill, but it saved his machines and thus cost.
We set up a 20 litre fuel can and marked it with what machine and what mix.
So he has 4 cans, Husky, Skill and cheepo and unmixed.
The fuel is mixed in the correct ratio in the calm of home. Saved so much trouble.
8ob
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You wont have any issues with Meteor, they are a quality aftermarket product. Those cheapy barrels are only any good for getting a saw running to sell on, not something I would do but like all this really cheap gear it gets it going and will give reasonable service life in the hands of domestic user.
Bob
Do you have a good source for the Meteor stuff @8ob? I've found a few kits on ebay but will take it all apart before ordering anything as there is mention of 10 and 12 mm pins and it is an old saw. Also curious to show you all what we find!
Happy to spend a decent amount to get a reliable machine. Its only had heavy use in my hands this last year. It could have had all sorts of abuse before that.
Happy to spend a decent amount to get a reliable machine. Its only had heavy use in my hands this last year. It could have had all sorts of abuse before that.
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Migmac
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When I cut professionally, I used to mix enough fuel up for a weeks work. Much easier doing “bulk” than mucking about with a combi cans worth of fuel
pedrobedro
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Mine is a 12mm pin and I bought a cheap piston just to see if it was a viable proposition with the refurbished Stihl cylinder. It's been good ever since and still pulls like a train. The original piston was well chewed. I use Aspen2 alkylate fuel now as it may stand for a month between uses and the fuel will stay in good condition. I use Aspen2 alkylate fuel nowadays, it is expensive but it doesn't go off if I leave it in the saw for a month between uses.
The_Yellow_Ardvark
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I believe my friend will mix 20kts up in one go. I think that will last him a week. The unleaded is kept in a jerry can. The other fuel in 20lt plastic containers.
Head off. Some pics below. Its just the front (exhaust side) of the piston and cylinder that is scored. How do I assess the big end bearing? It has a little side to side movement in the plane of the bearing but no up down so i dont think there is any play there? It turns freely and smoothly.
angellonewolf
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run your finger nail round the scratches on the bore are they light or does your nail dig in there
The_Yellow_Ardvark
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Oh no not gone.
Just camera shy.
Welded into the piston. I guess the piston was forced over by the other side.
Giving rise to some compression impression.
It would suggest the bore is oval, bottom end worn.
But the OP could melt it down and make Feng Shai art, sell it and buy a new saw.
pedrobedro
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The cylinder will not be scored, that is just transfer of aluminium from the piston. The one I did was far worse than that and it cleaned up perfectly and is still running as of Thursday this week. Apply some brick acid and you will see the aluminium fizz, when it stops repeat the procedure till there is no more reaction then neutralise it with some baking soda and rinse it well. Get some 240 grit wet and dry and WD40 sprayed in and rub it round to get the residue off. Fit the new piston and rings with some 2 stroke oil to lube and make sure the arrow on the piston is to the exhaust port side. The Nikasil plating in the bores is tough stuff and lasts for many years. It's usually the exhaust side where the seize happens due to the heat. Get the rod to the top of it's stroke then pull up on it to feel any big end play but it's not often they go. Side to side is normal in 2 strokes.
