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Stihl 261s Scoring Pistons

Started by JaredR, August 06, 2020, 09:15:08 PM

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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!



 

Al_Smith

Although it might be unpopular  i might throw my 2 cents in .First I assume it's a fresh air part transfer and assume it's set up for 50 to one oil to gasoline ratio.
From my perspective firstly 50 to one is too lean .Secondly the saw had to be tuned too lean .Thirdly using fresh air with no oil laden fuel is asking for trouble .Although you might blow most of the fuel out on  fuel laden transfer you leave the oil film on the cylinder .With fresh air it's less oil .
Now I know why they did it because of EPA mandates but that doesn't mean it's a good idea .-2 cents nothing more 

ZeroJunk

I have read the physics on why regular carburated two cycle engines don't like being run at half throttle. It was written before M Tronic etc. had been conceived , so not sure how that applies. But, the carburetors can be quite lean at half throttle. I don't know that it would ever be a problem limbing because the end destruction is heat, so even if it is lean you wouldn't be at a duty cycle high enough to melt the piston. But, if you are just steady cutting a log at half throttle you would.

joe_indi

50:1 on these saws is begging for trouble. Here I recommend customers to go for ' other oils' ratio which is 25:1. Going midway on these two would be a 30:1 for any oil. We don't have Mtronics here but the carburettor versions of stratified saws and usually to be on the safe side I adjust the carb more generously. This prevents over heating. We are working in 34 C temperature and for you to get your piston scoured like this the temperature needs to be much higher or the carb leaner

Ianab

I have heard of chainsaw carving guys having issues due to running the saws at part throttle for extended periods. The carbs on a chainsaw are relatively simple affairs, and are basically set to run at full throttle, or idle, as long as both those work, it's usually OK. They don't have the complicated fuel maps that a fuel infected car engine uses. The mixture might be wrong at 1/2 throttle, but saws don't usually spend much time running like that. 

A richer fuel/air mix and a bit more oil might help, but it's likely down to the operator. They aren't intentionally abusing the saw, but it's just not designed to be run like that. Let it idle, or give it the revs.  You might only be cutting through 2" sticks, but give it a blip of full noise to do it. That way it's not running lean, overheating AND starving for oil. 
Weekend warrior, Peterson JP test pilot, Dolmar 7900 and Stihl MS310 saws and  the usual collection of power tools :)

barbender

Sorry about your saws! While I don't like a 50:1 ratio, I sure doubt that's causing your issue. When I was was brushing and such log building, I tried to just continually blip the throttle, instead of holding it at continuous medium rpms. 
Too many irons in the fire

Spike60

50:1 isn't best for any saw, but it's at that ratio that modern saws will remain emissions compliant. That's why everything is supposed to be run at 50:1. I'm a 40:1 guy for my stuff; both newer AT saws and the old girls in the collection. But the deal here isn't the ratio, it's the constant 1/2 throttle running.

I think that just about every saw's owners manual will say that cutting should be done at full throttle. Probably more of a safety concern than anything. As far as leaning out at constant part throttle use I can see that happening. Every carb has a "lo" speed circuit and a "hi" speed circuit. There is no provision in the carb for low RPM running. At part throttle use, neither the lo or hi speed can operate as they are designed to. And low RPM's results in less cooling air from the flywheel.

Solution here would be a good electric saw run off a generator on the job site. Would also eliminate exhaust fumes as the house starts coming together and you are working in tighter areas. I don't think that you or the dealer would want to take a chance on burning up a 3rd saw.
Husqvarna-Jonsered
Ashokan Turf and Timber
845-657-6395

Patrick NC

I've never had any problems with 50:1. I used it in my ms260 pro for 10 years without a problem. Now I run a Husqvarna 372xtorq and a 550xp mk2 with the same mix. No problem yet. I only use premium synthetic oil ( husqvarna xp+ ) and never mix more than 2.5 gallons at a time. I agree with the theory of running full throttle when cutting. 
Norwood HD36, Husky 372xp xtorq, 550xp mk2 , 460 rancher, Kubota l2501, Case 1845 skid steer,

Al_Smith

Oh goody the oil wars again . 8)

Patrick NC

Quote from: Al_Smith on August 07, 2020, 09:45:24 AM
Oh goody the oil wars again . 8)
Sorry, I wasn't trying to say what was right. Just relaying my experience. If never argue for someone change what works best for them. 
Norwood HD36, Husky 372xp xtorq, 550xp mk2 , 460 rancher, Kubota l2501, Case 1845 skid steer,

Patrick NC

Autocorrect. I meant to say that I'd never argue to change what works for someone else. 
Norwood HD36, Husky 372xp xtorq, 550xp mk2 , 460 rancher, Kubota l2501, Case 1845 skid steer,

Al_Smith

 :D This great debate of oil mix and brand is a long standing type of debate going back as far as the internet and online forums .It can become amusing if you don't take it too seriously .

JaredR

Thanks for all of the replies, guys!

I took the carb one to the dealer this morning and he is going to tear it apart. He's curious if both saws came from the same batch.

As far as cutting with a full throttle, I don't think that applies to brushing. I've been told to run about half throttle and "blip" it as @barbender mentioned.

I'm going to wait to hear back from him, and am hoping that the saw has a defect. If it doesn't I'm not sure what to do as we've been following instructions from more experienced sawyers and builders. I've even asked Robert Chambers about it and we were using it as he recommends.

mike_belben

Saw carbs dont have much in the way of midrange metering circuits like a sled or bike. Its just idle and main jet, the midrange is just drilled passages at best.  

Id richen the mix and increase the idle time for cooldown breaks.  I sawmill with my 395xp at about 3/4 throttle all the time on the 87octane with the cheapest oil i can find, typically 30:1 and tuned fat.  I get a lot of vibration at WOT.  Lot of idle breaks to reject heat. 
Praise The Lord

lxskllr

Is that common knowledge saws shouldn't be run at 1/2 throttle? First I've heard of it. That should probably be put in the manual, with the reason given, instead of a generic "Cuts should be made at full throttle". I've run my mill at half throttle with the intent of letting it cool down a bit before going WOT again. Sounds like that's a bad idea.

gspren

I never heard or at least don't remember the why but my chainsaw mechanic said the throttle should be used like a light switch, all on or off.
Stihl 041, 044 & 261, Kubota 400 RTV, Kubota BX 2670, Ferris Zero turn

JaredR

Quote from: lxskllr on August 07, 2020, 03:02:11 PM
Is that common knowledge saws shouldn't be run at 1/2 throttle? First I've heard of it. That should probably be put in the manual, with the reason given, instead of a generic "Cuts should be made at full throttle". I've run my mill at half throttle with the intent of letting it cool down a bit before going WOT again. Sounds like that's a bad idea.
Same here. I'm also hearing a lot of conflicting info from multiple sources. The manual only says that you shouldn't run WOT until you use about 5 tanks. I didn't see anything about damaging it if used at 1/2. So apparently don't run it WOT or at 1/2, and if you do run it make sure it's under full load at all times. Or chance it burning up.  smiley_furious3 I think I will be seriously looking into battery chainsaws.

Al_Smith

 After I rebuild a saw I tune it fat,run a few tanks like that .Then lean it out and flog it like a rented mule .I don't baby them .

Real1shepherd

On the Swedish saws....no reason to baby them new or after a rebuild. Use a good oil mix and run them like you're gonna use them, hard.

As been said above, an electric saw is less bulky and gets into smaller spaces. Running a chainsaw half throttle most of the time is not getting enough oil mix in the works.

Kevin

JaredR

So are there any log builders here who have some input? How do you run your saws when notching and have you had this issue?

sawguy21

I have seen problems running at part throttle under load, the fan is not directing enough cooling air over the cylinder. The clutch also tends to slip and overheat. This is a real issue with trimmers/brushcutters. Run a 2 stroke like ya stole it, it also reduces the risk of kick back.
old age and treachery will always overcome youth and enthusiasm

ladylake

I've been running my trimmer at half throttle for 30years and it still works great.  Maybe its how they are tuned, I'd bet a little rich low helps, plus a little rich on high also. Too many now days are tuned on the edge of being lean, for sure the auto tune machines as they need to get by the EPA as they're sent out . Steve
Timberking B20  18000  hours +  Case75xt grapple + forks+8" snow bucket + dirt bucket   770 Oliver   Lots(too many) of chainsaws, Like the Echo saws and the Stihl and Husky     W5  Case loader   1  trailers  Wright sharpener     Suffolk  setter Volvo MCT125c skid loader

Al_Smith

On that lean run thing about 2 years ago before I retired I fixed one of those .It was a nearly brand new Echo about 50 cc's that never ran right,box store thing.
It had limiters on the jet screws .It was a simple task to just remove the tabs and tune it correctly . I've heard a dealer can't tamper with them .Last I knew I wasn't a dealer.It was set so lean it didn't have any power .It takes fuel to make power .
For a little saw it really ran pretty good.That little task was so simple the charge on that one was a 12 pack,not a case of beer . ;D

Al_Smith

On the above about an Echo saw don't be fooled by a name .That one was really a nice little saw after I tuned it and I have a nice weed wacker as well ..
I have another which is about 2 cubic inch rear handle chainsaw used by a tree trimmer until it suffered a fall like Humpty Dumpty .Broke the shock mounts .I repaired it ,rebuilt the carb etc .It is not a bad saw at  all,so old it runs 1/4" chain .Never judge a book by it's cover .

lxskllr

My two echos are my favorite saws; especially my 2511t. I like my Stihls a lot, and feel I got what I paid for, but it feels like the echoes(I'm always a little uncertain how to pluralize the brand) gave me more than I paid for.

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