How to fix an anti vibe buffer on a MS170

[Marc-Antoine]

Why does the exhaust side of the piston get so much abuse? I

Because it's the hottest point in the cylinder / piston assembly. The edges take the most heat and have a hard time to evacuate it. The aluminum is softened and shredded by the sliding. When the piston goes up, it collects the half melted debris or /and the edges collapse in the gap. The debris jam and weld themselves between the cylinder and the piston, creating many hardened points and generating an intense friction, rising even more the temperature and destroying the surfaces. The other sides don't see as much heated burned gas and more over, they are cooled by the incoming fresh gas.

 

[Nutball]

That was a 391 piston for those who overlooked the words in the post. The exhaust side was the worst, but about 80% of the piston was scored half as bad possibly from alignment changing with wear or the lack of oil. And I tried running it too on something like 32:1 or more 20w50 oil and that wasn't enough to plug the gaps and help it start. I don't even want to fix that one, $300 was spent on it used, and it lasted 2 weeks or something, then a new ignition was bought, now it needs $300 for a new P/C which could instead buy a new 271t with warranty and part out the rest for new chains and stuff.

 

[Al Smith]

So then is a 391 a later version of the 039/390 ? I don't know because that's another number I've never even seen let alone worked on .However if it is there's a zillion after market parts for the 039/390 models .Matter of fact all I've ever done on an 039 was repaired a faulty clutch .

 

[Nutball]

The thing that sucks is that the 391 cylinder is way different than the 390 and there are no aftermarket cylinders. The 311 cylinder might fit at a 2mm loss in bore, but it also isn't available in aftermarket parts. Both 311 and 391 cylinder are only available from Bailey's from what I could find for $300. The best I could do is probably get a cylinder for $250 at a dealer and an aftermarket piston for $20-30. A Husqvarna 455 aftermarket kit would be around $35! and I have one that isn't running at full power.

 

[Al Smith]

I looked it up .It's one of those so called low pollution contraptions ,49 cc bore . Throw the parts in a box ,in a given amount of time you'll find the repair parts . BTW using 20/50 wt oil is not a good choice for mix oil .

 

[Nutball]

20w50 oil is an experiment to see if it helps worn out low compression engines run better. It's what I use as bar oil usually, so it was readily available.

 

[Al Smith]

That thing swallowed something .Look at the divet in the top of the piston that pinched off both rings .In addition to that while heavy oil to a certain extend might help a worn out 4 cycle it has little or no effect on a two cycle .In addition to that addition once a piston gets scalded and produces "high spots" these break the surface tension of the oil film and you get metal on metal .

 

[woodworkingboy]

Maybe it swallowed a circlip off the piston pin. Break off a part of the ring and general havoc ensues.

 

[Burnham]

That is what we used to call "beat to shit, and worth as much" .

I'll say it again.

Trash, not worth the moolah in parts to fix that model, imo.

 

[Magnus]

I think the piston shown is overheated. Could be from lack of oil, then it will be scoorings almost all around piston.
Heat damages like this is often from crystallized or carbonized oil. Often you see some broken bits as well as this has in top.