MS260 muffler mod

Hi, there. Bought a second-hand MS 260 Pro in really nice condition, but good enough is never good enough.
Luckily it was one of the 260s that had an adjustable high speed screw (not all do). I hadn't seen this exact muffler mod posted in detail, so I thought I'd take some photos while I went step-by-step.

The muffler cover looks new because I have access to a sandblast cabinet. It really makes things easier to see and work on. This first photo shows the "before" shot of the opening. I'm not sure, but I suspect, that the previous owner may have opened it up a little. "H" mixture screw still had limiter cap, though.



This is the same shot with the hole opened up. Exhaust pulses exit this hole but have to immediately take a 90-degree right turn toward the frame, staining the area near the serial number. More on that later.



This is the outside of the cover showing where the exhaust comes out, but not before getting pushed back toward the opening by the flange of the heat shield. We'll fix that.



This is my first attempt at posting pictures. I hope it's working so far. Post continues below.

MS260 muffler, Part II

Whew! Made is so far!

Besides the hole size in the front of the case, there is another restriction. Part of the heat shield turns up and blocks some of the hole that was just opened up (red circle).



This is the same area ground away. Also notice that the flange from the heat shield that directed the gasses back downward has been bent up (blue arrow) -- away from the saw body.



OK. Now that we have the exhaust coming out with less restriction, now we have to take care of that staining problem. I fashioned a small steel plate to a proper shape to block the gasses from hitting the frame and direct them outward. I brazed the plate onto the outside of the cover.



Muffler cover back in place on the saw. It is hard to tell from this angle, but the brazed-on plate is just under the height of the root of the bumper teeth. It should not interfere with cutting at all.



So that's it! Some black exhaust paint, a twist of the "H" screw and we're good to go.

Hope it helps somebody else.

Looks like a neat job. When I modded my 026/260 mufflers, the power boost was good enough that I now run a 3/8" chain on an 18" bar, instead of the .325 chain. The 3/8" chain throws out larger chips and screams right through those logs. With the adjustable "H" jet you should be able to tune that saw nicely for using a 3/8" chain.

here is a fresh pic of a mod i just did on my 026, the hole is round just took pic on a angle, jus have to paint and bake then off to cuttin i go

West Texas said:

Looks like a neat job. When I modded my 026/260 mufflers, the power boost was good enough that I now run a 3/8" chain on an 18" bar, instead of the .325 chain. The 3/8" chain throws out larger chips and screams right through those logs. With the adjustable "H" jet you should be able to tune that saw nicely for using a 3/8" chain.

Click to expand...

I've timed both 3/8 and .325 square ground chain on my pretty heavily modded 260 and the .325 remains the fastest setup. I tested with .325-8 and a 3/8-7 sprockets. Both chains were Stihl RS that I ground on my Silvey. You can check out my YouTube videos for the proof.