What would cause this?

[neutral4x4]

Maybe running synthetic oil and not dino oil? That would explain the rings not being broken in. Either way, it seems strange to me that an iron ring would still have the lines on it and the harder nikasil cylinder wall is already glazed over where it should still have hone marks.

 

[bwalker]

Buildup like that can be caused by bad gas. Its also a given that it has been run hot.
I have also seen before that some engines just seem to have alot of buildup on the skirts like that for no apparent reason.
I havent fooled around with strato engines very much, but I do have a severely used redmax 8000 blower that's been to hell in back and its has no buildup like that.
If I had to guess I would say what we are seeing is caused by heat and not any sort of ring of cylinder finish issue. The area between the rings is clean so leakage past the top ring, which does most of the sealing is minimal. the intake side of the piston is also fairly clean as well.
I also would also be trying a different oil in it given the operating conditions and would not be afraid to go as high as 20:1 depending on the oil used.

 

[rms61moparman]

Brad,

That piston looks VERY similar to the one someone diagnosed as "milk jug syndrome" recently.
Something to do with the chemical breakdown of certain types of plastic when exposed to fuel mix.

Just a thought.

Mike

 

[blsnelling]

The area between the rings is clean so blow leakage past the top ring, which does most of the sealing is minimal.

Excellent point. You are absolutely correct. I hadn't noticed.

 

[Jacob J.]

Brad,

That piston looks VERY similar to the one someone diagnosed as "milk jug syndrome" recently.
Something to do with the chemical breakdown of certain types of plastic when exposed to fuel mix.

Just a thought.

Mike

That was my thought, or if he's buying gas at one of those rural mom and pop mini marts that don't move a lot of gas, there could be contamination.

 

[blsnelling]

Brad,

That piston looks VERY similar to the one someone diagnosed as "milk jug syndrome" recently.
Something to do with the chemical breakdown of certain types of plastic when exposed to fuel mix.

Just a thought.

Mike

His fuel container is a typical red plastic gasoline container, not disimiliar to my own. Are you talking about something besides a plastic gasoline container?

 

[blsnelling]

That was my thought, or if he's buying gas at one of those rural mom and pop mini marts that don't move a lot of gas, there could be contamination.

Where would that theory leave the obvious signs of obvious excessive heat?

 

[bwalker]

Brad, snap a pic of the pistons dome/ Moght be able to tell more from that.

 

[Metals406]

How are the mufflers on those saws Brad? If it has teeny little ports, that will cause more heat as well.

 

[blsnelling]

Brad, snap a pic of the pistons dome/ Moght be able to tell more from that.

Sorry, I already cleaned it off. It had minimal carbon buildup, with it's greatest concentration along the outer edges of the crown. Same with the combustion chamber. There was minimal buildup in the exhaust port.

 

[rms61moparman]

They are plastic but there are MANY different types of plastic as you well know.
I don't remember where I saw it discussed, but it seems that some of the cheaper jugs are made from a plastic that isn't compatable with fuel mix.
I remember that the worst were milk jugs and windshield washer fluid jugs but some regular gas cans were made of the same type of plastic just thicker.

Mike

 

[blsnelling]

How are the mufflers on those saws Brad? If it has teeny little ports, that will cause more heat as well.

Completely hollow with no baffles. I believe the exit hole is larger than a 460.

 

[bwalker]

Brad what did the areas where the exhaust port is located and where the transfers dump out look like?

 

[Metals406]

Completely hollow with no baffles. I believe the exit hole is larger than a 460.

Hmmmm. . . The more I think about it, the more I suspect the possibility of three things, and all the guys have been mentioning them.

1) Bad or contaminated fuel

2) Improperly tuned carb

And I have to wonder if this saw wasn't sucking air from somewhere and running lean to build so much heat??

 

[blsnelling]

Brad what did the areas where the exhaust port is located and where the transfers dump out look like?

Sorry, but I don't remember. I do remember that I could still see the arrow pointing towards the exhaust port. So that side was relatively clean. There is no errosion of the crown surface.

 

[blsnelling]

Hmmmm. . . The more I think about it, the more I suspect the possibility of three things, and all the guys have been mentioning them.

1) Bad or contaminated fuel

2) Improperly tuned carb

And I have to wonder if this saw wasn't sucking air from somewhere and running lean to build so much heat??

I don't think it would have survived milling if it had an air leak. I think we can also assume that it was tuned too lean for milling at least, since the limiter caps are unmodded. However, I noticed the plug was rather dark when I pulled it. Just something else to complicate things, lol.

 

[Metals406]

I don't think it would have survived milling if it had an air leak. I think we can also assume that it was tuned too lean for milling at least, since the limiter caps are unmodded. However, I noticed the plug was rather dark when I pulled it. Just something else to complicate things, lol.

Not saying it has had an air leak for long, just maybe the last few weeks of use? Lean failures can take a while, sometimes, esp. with good oil.

And now you tell us the plug color was good.

All I can say is, I know the flame itself wasn't traveling down the side of the piston, so the cooking effect was from conducted heat. Aluminum is 6 times more conductive than steel, so it doesn't take much for heat to travel from the top to the skirts.

I was gonna say this earlier but forgot. . . Isn't that saw on the smallish side to be a hardcore milling saw anyway?

 

[bwalker]

Brad, despite what some guys think its almost impossible to tell anything of value by looking at a plug unless done using the plug chop method. And even then you need a spark plug viewer to see the mixture ring.

 

[blsnelling]

I was gonna say this earlier but forgot. . . Isn't that saw on the smallish side to be a hardcore milling saw anyway?

Yes it is. This saw definately earns it's keep.

 

[Metals406]

Brad, despite what some guys think its impossible to tell anything of value by looking at a plug unless done using the plug chop method.

Very true. . .