MS391 found in trash..

[Tumleweed66]

A few years ago, I ran across a Stihl ms391 someone had discarded, it shows signs of being ran with no oil in the gas ( I'm no expert). I guess my question is do I put a cylinder kit and bearings/ seals in it or do I part it out? It looks lightly used other t6han the piston and cylinder..

 

[Huntaholic]

Id HAVE to fix that one! Clean the transfer out of the cylinder, clean and flush the crankcase, grab a new meteor piston with caber rings, and have a DANDY saw!

 

[cookies]

replace all the internal bearings and inspect the crank really really carefully if it was straight gassed, even the crank seals could be damaged. Looking at that piston it ran a while before coming to a suddenly halting demise.

 

[Tumleweed66]

A few years ago, I ran across a Stihl ms391 someone had discarded, it shows signs of being ran with no oil in the gas ( I'm no expert). I guess my question is do I put a cylinder kit and bearings/ seals in it or do I part it out? It looks lightly used other t6han the piston and cylinder..View attachment 962482View attachment 962483View attachment 962484

i'm sorry... screwed up my first post. It's an ms311, if rebuilt will be an ms391

 

[sawfan123]

That looks more like detonation than no oil. And it’s been going on for awhile.

 

[Tumleweed66]

Id HAVE to fix that one! Clean the transfer out of the cylinder, clean and flush the crankcase, grab a new meteor piston with caber rings, and have a DANDY saw!

the cylinder is ate up pretty good

 

[Tumleweed66]

That looks more like detonation than no oil. And it’s been going on for awhile.

it's funny cause the bearings have the plastic cages and they look and feel good. what would cause detonation like that?

 

[Wood Doctor]

the cylinder is ate up pretty good

Probably. You likely need to rebuild both the piston and cylinder. Add them together and these parts are not cheap. I doubt that the piston and rings alone would fix the problem. Lots of 291, 311, and 391 are sitting around unfixed because the replacement parts cost too much to fix them.

 

[Tumleweed66]

Probably. You likely need to rebuild both the piston and cylinder. Add them together and these parts are not cheap. I doubt that the piston and rings alone would fix the problem. Lots of 291, 311, and 391 are sitting around unfixed because the replacement parts cost too much to fix them.

that's why it's been in a box torn apart for a few years now but there is an oem piston and cylinder on the web for a few hundred alot better than 400

 

[Wood Doctor]

that's why it's been in a box torn apart for a few years now but there is an oem piston and cylinder on the web for a few hundred alot better than 400

That's still a bucket of cash. I can rebuild a 290 and/or 310 to a 390 for less than a $100 in parts these days. Time is on your side if you can simply wait longer. Even the dealers tell me that the OEM engine parts on these new Farm Boss saws are priced way too high.

 

[sawfan123]

it's funny cause the bearings have the plastic cages and they look and feel good. what would cause detonation like that?

Low octane.You don’t hear detonation on a 2 stroke.
It’s suppose to overload bottom end. Unless it doesn’t

 

[pioneerguy600]

i'm sorry... screwed up my first post. It's an ms311, if rebuilt will be an ms391

What would you like the title changed to? I can fix it for you.

 

[mountainlake]

Running lean. Steve

 

[Tumleweed66]

What would you like the title changed to? I can fix it for you.

ms 311. thanks

 

[bwalker]

That saw detonated for sure and wasn't straight gassed. Bravo! Never seen that in a saw.
As for causes. Crappy fuel. Running lean also makes detonation much more likely, although in a saw the compression ratios are so low that the engine typically seizes well before it detonates that badly.
I'm wondering if someone ran something like Coleman fuel through it?

 

[Patrick1903]

@Tumleweed66 Did you replace the piston/cylinder on this? I have a MS391 needing a new top end and was wondering how yours turned out.

 

[a. palmer jr.]

The Chinese haven't gotten around to cloning parts for that model of saw so there's no aftermarket for that one yet. Give them a few years and they'll flood the market with cheap parts..

 

[Patrick1903]

The Chinese haven't gotten around to cloning parts for that model of saw so there's no aftermarket for that one yet. Give them a few years and they'll flood the market with cheap parts..

Seems like a less popular model. Maybe its
My imagination but I don’t see or hear about them as much as many others online.

 

[hawkins111]

Yes, a 290, 310, 390 are all the same frame. However I don't think 291, 311, 391 are interchangeable! I could be wrong????

 

[Wood Doctor]

Yes, a 290, 310, 390 are all the same frame. However I don't think 291, 311, 391 are interchangeable! I could be wrong????

You are mostly right. The 311 and 391 have more interchangeable parts. These two models almost said good bye to the 291. Upgrading a 291 to a 391 is history. That party is over.