MS391 wont start

[treesap]

figured as much, ive been looking for anything that would stop it from running

compression has been 90psi since new as far as I know (Checked last year iirc, was 90, saw was almost new, maybe 5 tanks thru it)

time for a new piston? cylinder is fine as far as I can tell

 

[treesap]

It seems you fucked this saw up by asking what is essentially a home owner saw to do something it wasn't built to do...The results. She got crispy hot and you scored the piston. OOPS! Lesson learned?

to be fair, I told my dad milling with it was a bad idea, he still got a mill, and we still used it lol

defiantly coulda thought more first (Both of us), oh well, stuff happens

 

[Jehinten]

time for a new piston? cylinder is fine as far as I can tell

From your description, I'd say yes to the new piston. It's possible that the cylinder is ok, however your looking at the exhaust side of the piston and the intake side of the cylinder. The exhaust side of the cylinder could be damaged as well.


For what its worth, on a ms661. a cylinder, piston, fuel filter and muffler gasket cost $266 from a stihl dealer. I'd think that your saw would be a little cheaper

 

[rico]

to be fair, I told my dad milling with it was a bad idea, he still got a mill, and we still used it lol

defiantly coulda thought more first (Both of us), oh well, stuff happens

Don't feel bad... 1st tree on a new job this week and a dude on the crew missed his lay by 35 ft. My 550XP and my 562XP both fell victim to the 18ft Red...A $1500 fuckup... OOPS.

 

[treesap]

baileys has a piston, cylinder, pin and circlips for $375

hoping for the best lol, I did look at the cylinder from the spark plug hole looking at the exhaust side, it seems ok, as far as I can tell its time for a new piston and rings, about $25 everywhere im seeing them, now I just gotta find out if its a 47 or 49mm bore


fwiw I think a 661 may be in order for milling, I want a bigger saw anyways, dont need one, but I want one lol

 

[treesap]

Don't feel bad... 1st tree on a new job this week and a dude on the crew missed his lay by 35 ft. My 550XP and my 562XP both fell victim to the 18ft Red...A $1500 fuckup... OOPS.

ouch, send him a bill?

also, I wanna know how you miss something by that far, wind pushed it one it broke free? although if he had his holding wood intact it wouldnt push that far, operator error on his part as far as I can tell

 

[treesap]

for sure, speed kills, take your time and make every cut perfect, if you cant figure out how to make the tree go where you want (Notice I said make, not suggest) then you shouldnt be cutting them down

any questions about the job, full stop and figure out the answers, never failed me in the past

 

[Jonny]

Good to know the milling thing was your dad’s idea, and you didn’t just help yourself to his saw.
I had a fine running and clean looking 391 that I sold a friend last summer for 300$.
You’d be nuts to sink 375$ into that saw, in my opinion.

List it yourself or have a friend with a good feedback score list it on eBay, it’s stupid what some beat to shit saws will fetch there. Use them funds towards something new or a used pro saw.

 

[treesap]

selling it wont be an option, unless ive already bought a replacement, im gonna pull it apart soon and see what I can fix, new piston, rings, and wrist pin is $20, and that seems to be what most of the damage is, think it would be a good idea to hone the cylinder?

maybe I can find someone willing to trade for a 462, doubt anyone would make that trade tho

 

[treesap]

note to self, when milling, LET THE SAW COOL DOWN MORE OFTEN

 

[Jehinten]

think it would be a good idea to hone the cylinder?

A lot can be done to revive a cylinder with sandpaper, but doing too much can damage it. If there's any aluminum buildup inside the cylinder, you want to get it off before you start sanding through the chrome of the cylinder wall.

 

[Jehinten]

Start with a more aggressive paper to get the aluminum off quick. Randy Evans (Mastermind saws) said he starts with 80 grit. Not sure what he finishes with or how many steps he does

 

[treesap]

ive got an actually honing tool (3 spring loaded legs with fine grinding stone)
would be better than sandpaper, and worth a shot imo, wont open up the bore enough to where the rings wont seal

how much scoring on the cylinder is too much? there is almost always some, on the piston I was able so get my pinky finger down into the exhaust port and feel the scoring, doesnt look like much but if I can feel it with my fingernail, its way too much

I guess its time to pull it apart and check out the bore