GS461 unusual scoring, guesses?

[alexcagle]

This Stihl GS461 concrete chainsaw passed vac/press test.
Nothing out of the ordinary.
Clean fuel & air filters, well maintained saw.
Carb settings were correct.
Correct heat plug.
The damage did occur with temps in the upper 90's f
The saw Is about 1-1/2 yrs old and sees sporadic use.
The fuel was premium with Stihl ultra mix, and looks clean considering.
I think it's been overheated, possibly from getting in a bind.
But the damage is unusual to me.

 

[brandonstc6]

This isn't my expertise but was there any foreign debris in the cylinder or in the crankcase. One of those grooves looks really deep


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[davhul]

Is more of the scoring towards the clutch side? That's the hottest part of the cylinder

 

[Thommo]

Looks like something fell off inside there. i would be checking for broken bearing cages or rollers. It could also be a screw fell out of the carby or a broken circlip that has gone through it.

 

[davhul]

Maybe. Should have evidence of beating on top of piston

 

[MnSam]

I'd guess something came up through the lower end. The damage seems like it might line up with the transfers.

 

[davhul]

Could have. What's the cylinder look like

 

[blsnelling]

It's not lined up with the transfers. That is some odd looking damage though. Did the plating in the cylinder turn loose?

 

[davhul]

But you wound know if it overheated. There would be some plastic melted somewhere.

 

[TBS]

It's not lined up with the transfers. That is some odd looking damage though. Did the plating in the cylinder turn loose?

Something passed through the piston window and made a nice mark at the top part of the window opening in the bottom picture and came out on the clutch side tranfer.

 

[alexcagle]

Something passed through the piston window and made a nice mark at the top part of the window opening in the bottom picture and came out on the clutch side tranfer.

I noticed those marks after I posted too. Strange. That had to hit fast and hard to make those marks.

 

[alexcagle]

^^ This is it, after it was just removed. Note that there are no impact marks on the ceiling of the cylinder. ^^ Cleaned up great.^^

It's not lined up with the transfers. That is some odd looking damage though. Did the plating in the cylinder turn loose?

cylinder wasn't that bad, and cleaned up good.

 

[davhul]

Everything looks really dry. I would like to do a ethanol test on the fuel. You almost have 360degree scoring almost on 3 sides. You can see it slightly in that 2nd pic on first post.

 

[alexcagle]

I'd guess something came up through the lower end. The damage seems like it might line up with the transfers.

I suspected that too, but I diligently checked the bearing races, the lower rod bearing for integrity. No piston clips missing, no chunks broken off of the piston, no broken rings. No carb butterfly screws missing. I think I was the first person to take the clean air filters off to vacuum and pressure test the crankcase. For a year and a half of construction life cutting concrete pipe, the inside of this saw looks very clean.
The muffler had only aluminum dust inside.

 

[Andyshine77]

The transfer edges look fine, normally a foreign object will bang up the port edges and snap a ring or two. This may have in fact been caused by too much heat. A foreign object could do this of course, but without finding anything floating around you may never know.

That cylinder look perfectly fine so no worries there. More fuel and oil is never a bad thing IMHO.[emoji16]

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[blsnelling]

Speaking of oil, I wouldn't run that saw with anything less than 32:1. They have to run for long, extended cuts, similar to milling.