Stihl 261 v1 Carbon Scoring

[landlubber]

Hello,
I have a 261 carb saw that I purchased new. The saw has only run Stihl HD Ultra silver bottle at 45:1 or occasionally Stihl MotoMix at 50:1. I was bored and popped off the muffler and found this.

It looks like a piece of carbon has come loose and there is a mark through the lower ring, a groove in the piston and the chunk appears to be embedded between the rings in the piston. The cylinder, when inspected through the spark plug hole shows a corresponding mark that doesn't look like it has depth but the crosshatch is worn through.

This event has me switching oil and mix ratio and I've ordered a tach to tune the saw but I never suspected it of being overly rich. The saws compression is 160psi and the factory headspace looks to be about 0.038"

Options:
1 ) Change oil, mix ratio , tune and run it.
2) Teardown, inspect cyl and break glaze, new rings and buff out the piston
3) Sell it and buy an autotune 261


Thanks,
LB

 

[CR888]

Well I'd stop using full synthetic Stihl ultra oil for starters, that clearly ain't helping. Remove cyclinder, clean out/de-carbon exhaust port, squish area, piston crown. Inspect piston wear, and cylinder but I suspect that won't be bad. New OEM or caber rings & new piston if needed. And find an oil that won't get you into trouble in the future. Also clean spark arrestor with propane torch. Have you done compression test?

 

[Czed]

Can you feel the ridges on it?
If not run it with literally any other brand of oil than stihl.

 

[landlubber]

I've torn it down and cleaned up the piston. There is a score in the piston but the cylinder looks OK. I did a light de-glaze with scotch brite by hand. The compression was 160psi and squish was ~0.038" so I'm going to eliminate the ~0.017" base gasket or replace it with something much thinner.

While the saw is apart I'm considering advancing the timing (I've not done this before) but I'm still investigating what the appropriate change might be. The saw is used to limb and trim mostly so throttle response with a bit more heat would be OK for my use.

 

[Stihl Potlicker]

Hello,
I have a 261 carb saw that I purchased new. The saw has only run Stihl HD Ultra silver bottle at 45:1 or occasionally Stihl MotoMix at 50:1. I was bored and popped off the muffler and found this.

It looks like a piece of carbon has come loose and there is a mark through the lower ring, a groove in the piston and the chunk appears to be embedded between the rings in the piston. The cylinder, when inspected through the spark plug hole shows a corresponding mark that doesn't look like it has depth but the crosshatch is worn through.

This event has me switching oil and mix ratio and I've ordered a tach to tune the saw but I never suspected it of being overly rich. The saws compression is 160psi and the factory headspace looks to be about 0.038"

Options:
1 ) Change oil, mix ratio , tune and run it.
2) Teardown, inspect cyl and break glaze, new rings and buff out the piston
3) Sell it and buy an autotune 261


Thanks,
LB

@Redbull661 has done oil/mix testing. i quit using the Stihl oil, and started using Shaeffers 9000 at 32:1 and 40:1 with Efree 91 gas too. good luck trying to get a 261C my dealers i use ain't got any because of the Chinese Flu lock downs, so they are having a hard time getting the solenoids and such is what a Stihl rep told my dealer. but maybe he was just blowing smoke up his tailpipe.
i would get new rings and piston and do a bit of porting if you have the time too. even a mm will help.

 

[landlubber]

I cleaned everything up and installed new Stihl rings (0.008" end gap), gave the cylinder a quick de-glaze and made a copy paper base gasket (I had planned to eliminate the gasket but the deck had a minor step in it from the crank halves), re-assembled with some Permatex slacker2 and doubled the size of the factory muffler hole. Squish went from 0.037" to 0.026" and compression jumped from 160 to about 170+.

It runs great and sounds a lot more sporting.

 

[RI Chevy]

Cool. Good job. Where's the vids of this saw in wood? Lol
Come on now. You know the rules.

 

[landlubber]

YEAR UPDATE: The saw has seen moderate use and piston inspection show a nice oily piston and no carbon buildup. I have also advanced the timing 5deg.
Red Armour @ 40:1 and tuned to about 14,000RPM.

 

[RI Chevy]

Good deal!

 

[Wonkydonkey]

And still no vids,

errr he's a slacker

 

[PissRev]

I really like Stihl products except 4-mix and their oils. I'm glad the saw is running well.