Brown (combustion gas) stains on piston getting past the rings. Normal?

[777funk]

I notice near the exhaust port on my 026 that the piston has some brown (not black) varnish burning past the rings. On my FS81 weed trimmer it has the same but on the sides of the piston.

Here's what I'm seeing on the side of the FS81 piston (pictured):

Does this mean the rings are shot?

 

[link]

That's on the side, not in front where the exhaust port is.

 

[777funk]

That's on the side, not in front of the exhaust.

Correct. I'm referring to two different machines here (026 and an FS81) with similar combustion varnish on the piston. Pictured is the FS81.

I notice near the exhaust port on my 026 that the piston has some brown (not black) varnish burning past the rings. On my FS81 weed trimmer it has the same but on the sides of the piston.

Here's what I'm seeing on the side of the FS81 piston (pictured):

Does this mean the rings are shot?

 

[link]

That's original Stihl rings those lasts for 20+ years, not likely your problem.
I'd say that's residue from the exhaust getting in to the transfer ports before blowing back up in to the cylinder.
You could widen your exhaust port at the upper range before your transfers open to help that I guess.
Would gain some hp at high rpm too I would guess.

The compression exits the exhaust port, but moments later the transfer ports opens also. If the exhaust compression is not fully released when your transfer ports opens, the exhaust is going down the transfers before returning back in to the cylinder. That's what you see.

 

[Sepia]

You could also do a simple muffler mod to reduce the back pressure at the exhaust port.

 

[ericm979]

It's normal. I have seen that on a lot of two strokes.

 

[KASH]

Totally normal.
Kash