Piston scorch marks Advice

[stumpdaddykane]

Hey y'all,

I have two ms-261's that are both showing some scorch marks at the top of the piston on the exhaust side. They still seem to be running well and have good compression (by feel not with a gauge), and I can't see any scoring in the cylinder or on the piston. My question is, now that I've noticed the scorching, would I likely make this into a more costly repair by continuing to use them? Should I wait till more sypmtoms show up before learning how to dig into the cylinder? I mix the fuel for the crew mostly as 50:1 91 non oxy and Stihl 2 stroke oil. Any advice or suggestions appreciated.

Thanks.

 

[buzz sawyer]

What does the plug look like? How many tanks of fuel? I share your concern but it looks like it's getting plenty of oil. Just to be safe, have you put a tach on it and done a vac/pressure test?

 

[stumpdaddykane]

What does the plug look like? How many tanks of fuel? I share your concern but it looks like it's getting plenty of oil. Just to be safe, have you put a tach on it and done a vac/pressure test?

Thanks for the quick reply!
Plug looked like coffee with cream color which I've been told is good. Lots of tanks run through these. Probably three years old and see daily use through the winter. I have not and don't have one at the shop. Worth getting one?

 

[Tomos770]

Regarding all the goo around the exhaust port.....I saw pictures like that with stihl ultra..... Maybe these are just marks from all the ash/dirt your oil produces during the combustion....?

Change the oil you are using to cleaner burning one (FC/FD rated)

 

[ballisticdoughnut]

If they run good I wouldn't worry about it. Use good fuel mix, sharp chain, and send it all the way.

 

[Husky77]

nothing to worry about with the piston but lots of carbon in the exhaust port so probably on piston crown & combustion chamber too. Personally I would have it apart and give it a good clean, your saw will last longer and run better. Change to a cleaner burning oil also

 

[Patrick1903]

I mix the fuel for the crew mostly as 50:1 91 non oxy and Stihl 2 stroke oil.

Which oil?

 

[bwalker]

Just deposits from mediocre quality oil. These saws Mtronic?

 

[Stihl Learning]

Check the spark arrestor screen, probably carboned up too. I would use the Stihl Ultra 2-stroke oil and add some Seafoam to your mix, that will clean up and reduce the carbon buildup. If you keep running it like you are, the carbon will eventually build up and score the piston.

 

[Maintenance supervisor]

This is exactly why I switched over to Echo red armor, alot less carbon buildup.
Seafoam or Bearymans will clean up the inside of the cylinder and hopefully get the junk out from the rings. The exhaust port needs cleaned out also.

 

[Patrick1903]

The exhaust port needs cleaned out also.

What’s your preferred technique on doing that and not getting carbon back against the piston?

 

[Maintenance supervisor]

What’s your preferred technique on doing that and not getting carbon back against the piston?

I'll put the piston up to block the port soak it with Seafoam and use a sponge with scotch brite on one side and start scrubbing.
You've got alot in there though and the rings would be my main concern, pulling the jug and piston so they could be soaked in degreaser and cleaned would be what I would do if they were mine.
The parts are just fine now but that build up is definitely gonna get them.

 

[stumpdaddykane]

Damn thanks y'all.

Just deposits from mediocre quality oil. These saws Mtronic?

Yeah they're m tronic

 

[stumpdaddykane]

I'll put the piston up to block the port soak it with Seafoam and use a sponge with scotch brite on one side and start scrubbing.
You've got alot in there though and the rings would be my main concern, pulling the jug and piston so they could be soaked in degreaser and cleaned would be what I would do if they were mine.
The parts are just fine now but that build up is definitely gonna get them.

Ok will do. Thanks

 

[stumpdaddykane]

Check the spark arrestor screen, probably carboned up too. I would use the Stihl Ultra 2-stroke oil and add some Seafoam to your mix, that will clean up and reduce the carbon buildup. If you keep running it like you are, the carbon will eventually build up and score the piston.

I'll try the sea foam. Since we use the stihl ultra exclusively, what might that buildup be from if not mediocre oil?

 

[bwalker]

I'll try the sea foam. Since we use the stihl ultra exclusively, what might that buildup be from if not mediocre oil?

It's from Ultra.

 

[bwalker]

As for Seafoam. That stuffs snake oil. Never seen it do a damn thing to remove deposits from a two-stroke. Mercury Marine power tune is a product that will help remove carbon.
In all honesty if you start running a good quality Jaso FD oil it may clean up on its own.

 

[Stihl Learning]

I'll try the sea foam. Since we use the stihl ultra exclusively, what might that buildup be from if not mediocre oil?

How are you measuring your oil/fuel mix, looks like just too much oil. I have used the Seafoam many times and have seen black fluid running out of the muffler.

 

[Fatherwheels]

How are you measuring your oil/fuel mix, looks like just too much oil. I have used the Seafoam many times and have seen black fluid running out of the muffler.

I think its not too much oil, its just the oil he is using, three years with Ultra
and that is the result.
If it was my saw, I would take the cylinder off, clean it, remove the piston
and clean it, and add two new rings, and change to a different oil.
There is no point in waiting until some of the crap gets lodged between the piston and cylinder and causing a melt down, loosening it with snake oil will only result in the same when the deposits get trapped between cylinder and piston.

 

[OM617YOTA]

I'll try the sea foam. Since we use the stihl ultra exclusively, what might that buildup be from if not mediocre oil?

Stihl Ultra is the mediocre oil being discussed.

If they were my saws, I wouldn't tear them down. I'd switch to Echo Red Armor, run them, and monitor the situation, with the expectation that it would clear itself up.