MS260 cylinder score?

[MaddBomber]

It's an '08, put it's 204th tank through it today. Yes, I'm that OCD that I keep track. Anyway, I stripped and cleaned it thoroughly. It sees 90% hardwoods.
Well maintained. 40:1Stihl HP Ultra


Theine between the top of the piston and top ring? Did it just chew up a wood chips or do I have an issue?
*plus the top left edge.



Lovely amber varnish. Switching to Saber oil ASAP.


Not a bad looking saw for how much she's been used. She's limbed many thousands of trees.

Any input on what caused the marks on the piston would be greatly appreciated.

 

[drf255]

Kinda looks like a crack.

Don’t think it’s scored because it doesn’t follow through to the rest of the slug.

Get some more pics, see if you can get the edge of the crown to see if it follows through like a crack would.

Probably just a carbon scratch from that Stihl Ultra.

 

[jltrent]

Looks like it has been running to rich, probably has a little carbon scoring judging from the buildup I can see in the pic.

 

[MaddBomber]

Okay, I pulled the cylinder. The mark on the piston does not appear to be on the top. Definitely think I've got an issue with carbon build up.



Definitely some light scoring.




Odd wear pattern on both intake and exhaust sides. (The flecks are lint from towel).
Any advice on removing the carbon? Or just replace the piston?

 

[Mad Professor]

Running way rich. What oil/gas mix and how is carb tuned?

There are OEM stihl pistons (no pins) listed on ebay for $35. Clean up cylinder

 

[MaddBomber]

Running way rich. What oil/gas mix and how is carb tuned?

There are OEM stihl pistons (no pins) listed on ebay for $35. Clean up cylinder

40:1 Stihl HP Ultra is 95% of mix used. Tuning is obviously my fault. Thought that running her fat would lengthen life... Guess that plan backfired! Lol.

I plan on lightly honing the cylinder and cleaning up the exhaust port with Dremel. Definitely going to get one of those pistons. Thank you for the tip!


FWIW... The MS261/MS362 dawgs fit the 260/026. They're a bit more aggressive than the anemic original, without being crazy left coast style.

 

[drf255]

Don’t hone it with anything but scotchbrite.

Thats a good looking cylinder.

Tune it by ear and nix the Ultra, it sucks. Pick another quality oil.

 

[MaddBomber]

Don’t hone it with anything but scotchbrite.

Thats a good looking cylinder.

Tune it by ear and nix the Ultra, it sucks. Pick another quality oil.

Will do. Thank you!

 

[rupedoggy]

204 tanks and now you want to change something. ARE YOU CRAZY

 

[dmb2613]

The Ultra is great if you run it 50 to one , it will carbon up at 40 to one. Follow the directions on bottle. If you want to run 40 to one use the orange bottle, I am a Stihl Dealer and I run 40 to one orange bottle.

 

[MaddBomber]

204 tanks and now you want to change something. ARE YOU CRAZY

Yes, as a matter of fact I am. Even got the paperwork to prove it! Lol.
But seriously, I love this little saw. I have more hours on it than any other (a lot of limbing in New England hardwoods). I had planned on doing a full inspection and partial rebuild for awhile. The carb has been a bit wonky (probably due to the horrid filtration), and she might have a vac/pressure leak.
Definitely a new piston, port cleaning, carb rebuild, filters and fuel lines.

 

[MaddBomber]

The Ultra is great if you run it 50 to one , it will carbon up at 40 to one. Follow the directions on bottle. If you want to run 40 to one use the orange bottle, I am a Stihl Dealer and I run 40 to one orange bottle.

I just may do that. I've got 12 bottles of Ultra (1gal mix) that I bought for the extended warranty on a blower and trimmer. I'm fully depending on my MS362c, and I've heard that M-Tronic saws do better on 50:1.

 

[Tinman204]

I used to run stihl oil exclusivly but i find its bad for carbon build up even at 50:1.

Switched to optimol and have zero carbon issues since.

No more stihl oil for this guy..