What would cause this?

[blsnelling]

I've got my strong suspicions, but would like to see what you guys think. This P&C is off a good running MS441. Compression cold was about 142 PSI. None of the "marks" in the cylinder can be felt at all. The rings still have the little micro lines in them like new ones.

So two questions here. What caused the marks in the cylinder? What caused all the carbon on the piston?

 

[blsnelling]

 

[BloodOnTheIce]

Hmmmm two strato saws, both with excessive amounts of carbon build up has me baffled. And I've run this saw and it runs really strong.

 

[blsnelling]

Hmmmm two strato saws, both with excessive amounts of carbon build up has me baffled. And I've run this saw and it runs really strong.

I think there's a legitamate explanation for this one.

 

[Metals406]

Plugged (Poorly flowing) muffler, mixed with an overly rich tuning??

Beats me, that's weird.

 

[WoodChuck'r]

That's bizarre. And yeah, I've run the saw as well - he's my neighbor, lol.

I dunno. I've never seen anything quite like it. Running too rich maybe??

What are your guesses Brad??

 

[bwalker]

I think there's a legitamate explanation for this one.

Strato saws run hotter than regular two strokes and use less fuel to boot(ie less coolant). Add to that that most chain saw oils are fairly low in quality and you have a piston looking like the one posted.
FWIW its not that bad.
I havent a clue how that mark of the intake port got there

 

[blsnelling]

Do you have any guesses Brad??

I do, but I want to get honest, unbiased opinions first.

 

[blsnelling]

There was some carbon buildup on the piston crown and in the combustion chamber, but not bad. The saw has had WoodlandPro synthetic oil it until the last 4 tanks when it has Stihl Ultra in it. I don't think oil is the culprit. If anything, I think good oil helped save it.

 

[WoodChuck'r]

This just boggles my mind currently.

Wow am I ever lost.

 

[WoodChuck'r]

****ty gas??

 

[WildnCrazyGuy]

My guess is the factory is setting them leaner and leaner nowadays... Carbon??? No clue.

 

[matt9923]

Interesting, Id have to see the saw and how it was in its "working" condition.

I have an idea.

opcorn:

 

[WoodChuck'r]

The thing that's REALLY confusing me here is I know that saw! I've run it a bunch of times and (since we're neighbors) I hear it running all the time.

It runs strong as hell and doesn't sound strange at all.


Good god this has got me stumped. Frikkin' weird!!

 

[blsnelling]

I'm not trying to play games with you guys, so here's my opinion of what caused this. Plain and simple...heat, and lots of it. The carb on this saw still has the limiter caps on it and has been used for milling, even in 90° heat. I believe this saw has been hot enought to almost seize. I believe a tight piston caused the marks in the cylinder. I also believe extremely high heat is what baked the oil onto the piston. Had this saw not had good synthetic oil in it, I don't think it would have survived. This here is an advertisement for the benefit of using good oil.

 

[WoodChuck'r]

Interesting. Yeah he does mill with it ALL the time.

Makes me curious about my 7900 - I mill with it quite a bit (even hardwood) and sometimes that saw gets HOT!!

 

[Metals406]

I'm not trying to play games with you guys, so here's my opinion of what caused this. Plain and simple...heat, and lots of it. The carb on this saw still has the limiter caps on it and has been used for milling, even in 90° heat. I believe this saw has been hot enought to almost seize. I believe a tight piston caused the marks in the cylinder. I also believe extremely high heat is what baked the oil onto the piston. Had this saw not had good synthetic oil in it, I don't think it would have survived. This here is an advertisement for the benefit of using good oil.

Makes sense to me. . .

 

[buzz sawyer]

I've seen carbon build up like that on 4 cycle from poor fuel and hot soak. Maybe using the choke to shut it down instead of off switch? The residual heat in the engine reduces the excess fuel to the caramel / carbon deposit.

 

[matt9923]

Improperly set up milling saw= Bad.

Surprised it didn't seize even with synthetic. what mix ratio?

 

[blsnelling]

Most saws seem tp be tuned on the lean side for normal bucking. That's way too lean for milling. I think the solution here, is more oil in the mix, and tuned rich enough that it barely quits 4-stroking under load.

BTW, there also appears to have been a fair amount of dirt ingestion. I would suspect this is due to the far dustier conditions of milling. This might be another good application for oil on the filter.