Stihl MS 391cylinder scoring

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Jimmyjam

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Hello all, I have been milling with the ms 391 for the past year and just recently had it fail. It will start go straight to high idle then shut off after about 10 seconds. I have had it for a little for less then a year and I'm being told by the dealer the warranty is void due to the description given by their service dept. As they say it shows signs dirt has passed the air filter and damaged the cylinder. I have been religious about cleaning the saw after each use and also changing the air filter. Either way this is where I'm at. They told me repair and parts would cost approximately $800 which is almost $200 more than what I paid. Hoping to get some advice or direction. I've been milling for several years and never had an issue like this, I have worked on my saws on some minor issues but nothing like replacing the cylinder or piston. The final description is scoring on cylinder and piston. Any advice or video links is much appreciated. From what I've found this sounds to be a common problem with this saw. Thanks
 
Hello all, I have been milling with the ms 391 for the past year and just recently had it fail. It will start go straight to high idle then shut off after about 10 seconds. I have had it for a little for less then a year and I'm being told by the dealer the warranty is void due to the description given by their service dept. As they say it shows signs dirt has passed the air filter and damaged the cylinder. I have been religious about cleaning the saw after each use and also changing the air filter. Either way this is where I'm at. They told me repair and parts would cost approximately $800 which is almost $200 more than what I paid. Hoping to get some advice or direction. I've been milling for several years and never had an issue like this, I have worked on my saws on some minor issues but nothing like replacing the cylinder or piston. The final description is scoring on cylinder and piston. Any advice or video links is much appreciated. From what I've found this sounds to be a common problem with this saw. Thanks
@Jimmyjam i bought a MS391 last year from a guy who bought it specifically to mill with. His failed, but due to straight gassing it. I had a thread on here showing the saw and how I salvaged the cylinder, and just replaced the piston and seals. I was going to replace the cylinder too but decided to experiment with cleaning it up and trying to salvage the Stihl cylinder. I had mostly aluminum transfer from piston to cylinder walls. Otherwise some light scoring. Pics are in thread below. I’ve only run 4 or 5 tanks through it but it’s been strong running. I have an extra piston and cylinder (actually 2 new Hyway cylinders, 1 piston) if you’re interested in rebuilding the top. They’re the 3 bolt design…there are two different designs for this saw IIRC.

Others have said on this site that they clamshell saws can struggle with milling (as far as longevity of the saw) since the design doesn’t allow the saw to absorb heat on the bottom end as well. That was my interpretation anyway.

https://www.arboristsite.com/threads/ms391-top-end-rebuild-project.359708/
 
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