Stihl 261s Scoring the Cylinder

[JaredR]

Hi all,

I'm new to the forum and looking for some answers. We recently started building handcrafted log homes so I went to the local Stihl dealer and bought a 261 C-M for our notching and small saw work. After using it a few days (less than 10 hours on the saw) it wasn't starting and obviously had a problem. Took it back to the dealer and he takes the muffler off and the cylinder and piston are scored badly (see photo) and he said the only time he had seen that happen was from unmixed fuel. However, we are running Stihl mixture at the suggested ratio and because we have built a good relationship with him he decided to look into it further instead of just saying we ran straight gas in it. He called his "higher-up" who asked what we were using it for and when he heard it was for log building he said immediately that the usage was too light and the saw had somehow self-adjusted and was over-revving, burning itself up. (We do a lot of brushing and light cutting, running it at half throttle). Apparently they had ran into this before with the smaller C-M models and log builders.

While he is replacing the piston and cylinder under warranty I went ahead and bought a regular carburated 261 which we have been using and it's been running great. However, this afternoon my brother sent me a photo of the piston on the new one and said it's scored and not starting. I have no idea what is causing this. Do Stihls seriously self-destruct if not ran under constant load? I'll be taking the saw back to dealer tomorrow as well as our 15gal tank of mixed gas that we have been using but would like to get some outside thoughts on this.

Thanks very much and I hope this is in the correct forum.

 

[John Lyngdal]

OUCH....
You're using Stihl canned fuel in these saws? I think that fuel has fuel stabilizers mixed in, so the "bad, stale" gas cause isn't as likely of a cause.
Since the carburetor isn't self adjusting on the non-M saw, it might have been adjusted too lean which can lead to piston damage.
The good news is that it's likely only the piston is damaged.
If they were my saws, I'd be running Ethanol-free pump gas and Amsoil Saber at 40:1
Just haven't been that impressed with Stihl Ultra oil reports.

 

[Maintenance supervisor]

If stihls self destructed every internet hero " piss revving " one for the camera would blow one up every ten minutes!
That type of scoring is usually caused by an air leak or strait gas.
Was the fuel mixed? Like really mixed?
Has it been sitting around for weeks?
Could it be sabotage, ex- employee?
Dealer selling you remans?

 

[JaredR]

OUCH....
You're using Stihl canned fuel in these saws? I think that fuel has fuel stabilizers mixed in, so the "bad, stale" gas cause isn't as likely of a cause.
Since the carburetor isn't self adjusting on the non-M saw, it might have been adjusted too lean which can lead to piston damage.
The good news is that it's likely only the piston is damaged.
If they were my saws, I'd be running Ethanol-free pump gas and Amsoil Saber at 40:1
Just haven't been that impressed with Stihl Ultra oil reports.

Thanks for the reply!
We bought a gallon of the premixed gas and then went to buying the small containers and mixing it ourselves. So the C-M ran some pre-mixed and then 87 octane with the mix added in.
The saw non-M saw was setup by the dealer and I was going to take it in next week for a checkup/tuneup (I bought it last Friday).
I'll definitely check out that oil and we have been using premium (91 octane?) fuel in the new saw.
Incidentally we have been running the same fuel in our new 661 C-M with no issues, but it is usually ran under load.

If stihls self destructed every internet hero " piss revving " one for the camera would blow one up every ten minutes!
That type of scoring is usually caused by an air leak or strait gas.
Was the fuel mixed? Like really mixed?
Has it been sitting around for weeks?
Could it be sabotage, ex- employee?
Dealer selling you remans?

Thanks for replying!
The fuel has all been mixed. I mean, we don't stir it, but it gets put in a gallon can and shaken around or recently we started using a 15gal tank and added the mix then filled it with gas then it rode in the back of the truck for a couple of miles.
Most of the fuel is being used within a week of being bought and mixed. All of it within two weeks.
The fuel is being mixed by myself or my brother. My other two employees are a sister-in-law and a close friend and I have never had an issue with them. No ex-employees and it's all in a locked yard and shop.
I don't get the feeling that the dealer is the type to do that and he honored the warranty on the C-M. Haven't taken the non-M one in yet.

I am not a pro logger but I have ran saws before and my brother has run them quite a bit and we've never seen this happen.

 

[ammoaddict]

That's just crazy.

Sent from my moto g(7) power using Tapatalk

 

[sean donato]

I bet it has something to do with the half throttle operation. I'd be keen to see what the dealer has to say about the non mtronic saw. I've heard of carbed saws having issues running part throttle, but how I understand the mtronic is it leans the saw out every now and then and looks at the rpm fluctuations to determine if its fuel ratio is good. Thus it shouldn't be able to purposely run lean at any rpm..... but I have also been told that a new mtronic saw needs worked to calibrate the electronics properly.

 

[grizz55chev]

I just worked on a Husky 135 that came to me because it wouldnt idle no matter how i adjusted the throttle stop screw. This saw was bought from a dealer in town that doesnt service, just sells em. Customer took the saw to a shop that works on and sells Huskys, they said they could look at it under warranty next month, so i took a look at as a favor. this is a model i havent had any previous experience with, so i tore into it thinking its gotta be a fuel delivery problem, maybe a bad fuel line or clogged screen in the carb, both checked out fine. for anyone that gets one of these little homeowner saws, beware! that carb was a sob to get off as its a stratto model and its stuffed in there pretty tight. After a full inspection of the fuel system and finding nothing wrong, the next step was to attempt an adjustment of the low end screw to see if it was in fact set lean at the factory, sure enough, after backing the screw out ( it has the splined screws that are a pain to adjust without the proper tool, which i dont ), i finally got it sorted out. I figure it was finally broken in and badly needed a tune , so maybe your saws are in a similar situation?

 

[sean donato]

That would make sense for the second saw, but not his mtronic saw, should adjust itself.

 

[JaredR]

I bet it has something to do with the half throttle operation. I'd be keen to see what the dealer has to say about the non mtronic saw. I've heard of carbed saws having issues running part throttle, but how I understand the mtronic is it leans the saw out every now and then and looks at the rpm fluctuations to determine if its fuel ratio is good. Thus it shouldn't be able to purposely run lean at any rpm..... but I have also been told that a new mtronic saw needs worked to calibrate the electronics properly.

According to his "higher-up" in Denver if you run the M-Tronics lightly they somehow keep adjusting themselves to run faster and will eventually burn up. They first had that issue with landscapers who were just cutting bushes and light stuff and then again when log builders started buy them. Which I'm sorry, but that seems like a flawed design.

I just worked on a Husky 135 that came to me because it wouldnt idle no matter how i adjusted the throttle stop screw. This saw was bought from a dealer in town that doesnt service, just sells em. Customer took the saw to a shop that works on and sells Huskys, they said they could look at it under warranty next month, so i took a look at as a favor. this is a model i havent had any previous experience with, so i tore into it thinking its gotta be a fuel delivery problem, maybe a bad fuel line or clogged screen in the carb, both checked out fine. for anyone that gets one of these little homeowner saws, beware! that carb was a sob to get off as its a stratto model and its stuffed in there pretty tight. After a full inspection of the fuel system and finding nothing wrong, the next step was to attempt an adjustment of the low end screw to see if it was in fact set lean at the factory, sure enough, after backing the screw out ( it has the splined screws that are a pain to adjust without the proper tool, which i dont ), i finally got it sorted out. I figure it was finally broken in and badly needed a tune , so maybe your saws are in a similar situation?

Apparently we can't even run the long enough to break in. We cut some firewood for about an hour with the carbed model but now it's having issues.

That would make sense for the second saw, but not his mtronic saw, should adjust itself.

See my reply to your other post.

 

[Maintenance supervisor]

Ok so I just read about twelve "break in" threads and alot of people who are long timers on the site who actually use saws (not just internet cruisers) say to avoid wot with no load for the first 10 tanks or so.
Not sure how your running the saws but if its being run wide open from start to stop brand new maybe its more of a cold seize problem?
I've trained guys on chainsaw who the second the saw starts they grab that trigger and dont let go! But the saws are usually pretty old and beat already.

 

[sean donato]

Normally that's a 4 point seize. And no shouldn't piss rev them cold, they need warmed up a bit first. Then put to work. Rings needs dynamic load to seat, ie worked. just light revving wont help anything. What your dealer have to say about the new saw?

 

[JaredR]

Ok so I just read about twelve "break in" threads and alot of people who are long timers on the site who actually use saws (not just internet cruisers) say to avoid wot with no load for the first 10 tanks or so.
Not sure how your running the saws but if its being run wide open from start to stop brand new maybe its more of a cold seize problem?
I've trained guys on chainsaw who the second the saw starts they grab that trigger and dont let go! But the saws are usually pretty old and beat already.

Ok. Well, we aren't running them wot but they do get half throttle with low load.
I guess I'm going to have to cut several cords of wood before using the saws as needed.

Normally that's a 4 point seize. And no shouldn't piss rev them cold, they need warmed up a bit first. Then put to work. Rings needs dynamic load to seat, ie worked. just light revving wont help anything. What your dealer have to say about the new saw?

I've always seen saws started and then revved a couple of times before being loaded, but I know that doesn't mean it's correct. That's why I'm here learning. I will be taking it in this morning so I'll let you guys know what he says. I think I'm going to need to run a richer mixture.

 

[cuinrearview]

Ok. Well, we aren't running them wot but they do get half throttle with low load.
I guess I'm going to have to cut several cords of wood before using the saws as needed.



I've always seen saws started and then revved a couple of times before being loaded, but I know that doesn't mean it's correct. That's why I'm here learning. I will be taking it in this morning so I'll let you guys know what he says. I think I'm going to need to run a richer mixture.

A richer mixture creates an even leaner air/fuel mix.

 

[JaredR]

So I took the carb one in this morning and he is going to take it apart. He started out saying we had to be running a lean mixture but after we talked some more and I told him he can test the fuel and I would even bring the tank we are using over he wants to take it apart. He's curious to see if both saws are from the same batch and maybe there's some kind of defect.

 

[JaredR]

A richer mixture creates an even leaner air/fuel mix.

Ok. Well, that's why I used the premixed then the recommended mix. Still pretty new and learning a lot.

 

[Maintenance supervisor]

A richer mixture creates an even leaner air/fuel mix.

You mean the oil to gas mix ratio or adjustment of the needle?

 

[cuinrearview]

You mean the oil to gas mix ratio or adjustment of the needle?

Both. More oil at the needle equals less fuel to air into the engine.

 

[CR888]

While running a saw at half throttle for prolonged periods is asking for trouble, to burn up 2 saws in such a short time for me rings an alarm bell that its fuel related. You say you get your gas from a 15gal mix container. That's pretty big how do you mix the oil into that container properly? How does it stay fresh? Is it stored outside? Just remember if they test your gas and its got water in it, they'll likely not warranty the expensive repair. I'd test your gas yourself first.

 

[sean donato]

I run 40 to 1, never cared for 50 to 1. Guess it because I remember 25 to 1 then 30 to 1, and when we used straight 30 weight engine oil to mix. Besides t stroke oil refinement and the advent of synthetic oils, the epa has been the main reason for such low oil ratios. (Not trying to get into a debate over oil ratio or types here) It's a simple carb adjustment, and the mtronic/ auto tune carbs I've ran havent had an issue adjusting to the new ratio. But you are 100% correct, more oil leans the fuel mix at the same needle setting.

 

[JaredR]

While running a saw at half throttle for prolonged periods is asking for trouble, to burn up 2 saws in such a short time for me rings an alarm bell that its fuel related. You say you get your gas from a 15gal mix container. That's pretty big how do you mix the oil into that container properly? How does it stay fresh? Is it stored outside? Just remember if they test your gas and its got water in it, they'll likely not warranty the expensive repair. I'd test your gas yourself first.

That first picture is from the CM saw and it only used Stihl premixed fuel and then Stihl mix in 87 octane fuel mixed in a 1gal can at a 50:1 ratio.

The second saw used Stihl mix at a 50:1 (actually slightly richer) ratio with 91 octane fuel. 6 6.4oz bottles we're poured in, then it was filled at a gas station moving the nozzle around to mix it up then rode in the back of the truck sloshing around. The hose for this tank is near the bottom.

For everyone thinking this is a fuel issue (I know, that's the most obvious thing), the exact same fuel used in both of these saws has been used in a 661 CM with twice as many hours as they had and it has had no issues.