Kick myself in the butt! 371XP smoked

[bitzer]

I get bark to the point that it is smoldering all the time with my 440. dont look like it was "heat blistered" to me, never heard that term before when talking about a spark plug, color looks typical to me. not lean and not hot.

I believe it, just never seen it actually light. Heres a spark plug chart that mentions blistered on the overheated plug. The picture is not great, but there are several other charts if you search online that mention blistering. Don't know how common this would be in chainsaws though. Just my thoughts.

I don't think ethanol would be a major contributor to this, but it definetely wouldn't help anything.

 

[bitzer]

I just found this series of pages from NGK spark plugs regarding spark plug color, fuel additives in low quality fuels and effects of altitude that cause certain plug conditions to occur. Interesting and worth the read. I could see how a lean mix and certain fuels and additives could cause lots of problems.

http://ngksparkplugs.com/tech_support/spark_plugs/index.asp?mode=nml

 

[scootr]

Interesting!

Cool link Bitzercreek! I know my saw was not running lean at high altitude. I talked to the fuuel delivery man today, he said they started the winter blend last month. Now after reading about additives, some things are becoming more clear.

Fuel Type / Quality

* Low quality and/or low octane fuel can cause knock which will elevate cylinder temperatures. The increased cylinder temperature will cause the temperature of the combustion chamber components (spark plug, valves, piston, etc.) to rise, and will lead to pre-ignition if the knock is uncontrolled.
* When using an ethanol blend fuel with high ethanol content in high performance applications, a colder heat range may be necessary. The spark timing can be advanced further because ethanol blend fuel has a higher resistance to knock (higher octane). Due to the decreased knock, there will be less audible “warning” from knock before the spark plug overheats and pre-ignites.
Some types of fuel additives in lower quality fuels can cause spark plug deposits that can lead to misfires, pre-ignition, etc.

 

[scootr]

More info

Ambient Air Temperature / Humidity

* As the air temperature or humidity decreases, the air density increases, requiring a richer air-fuel mixture. If the air-fuel mixture is not properly richened, and the mixture is too lean, higher cylinder pressures / temperatures, knocking, and the subsequent increase in the spark plug tip temperatures can result.
* As the air temperature or humidity increases, the air density decreases, requiring a leaner air-fuel mixture. If the air-fuel mixture is too rich, decreased performance and/or carbon fouling can result.

Barometric Pressure / Altitude

* Air (atmospheric) pressure and cylinder pressure decrease as altitude increases. As a result, spark plug tip temperature will also decrease.
* Fouling can occur more easily if the air-fuel mixture is not adjusted to compensate for the altitude. Higher altitude = less air = less fuel.

 

[Terry Syd]

detonation

I've seen plugs where the engine has been detonating and the center electrode will show bits of carbon burnt on that were blasted from the combustion chamber. I can't really make out from the picture if that condition exists on the electrode.

You were putting the engine into a high load situation, so perhaps there was some detonation going on. If so, once the engine starts to detonate the temperatures rise very rapidly.

A picture of the piston may give us a better indication of what happened. If it went into detonation and heat seized, then the crown may give us a clue.

 

[scootr]

Piston pics

Here is some pics of the piston. I'm thinking it was a combination of things. Lower altitude, cooler temps, crappy gas and Heavy load (detonation). It is getting new seals along with the piston. All the lines were in good shape, and everything was tight. I WILL check for 4 stroking every time I use it, from now on.

Oh yea, carb is getting rebuilt also, making sure it gets plenty of fuel. Speaking of fuel, how long does Av-gas keep?

 

[bitzer]

Here is some pics of the piston. I'm thinking it was a combination of things. Lower altitude, cooler temps, crappy gas and Heavy load (detonation). It is getting new seals along with the piston. All the lines were in good shape, and everything was tight. I WILL check for 4 stroking every time I use it, from now on.

Oh yea, carb is getting rebuilt also, making sure it gets plenty of fuel. Speaking of fuel, how long does Av-gas keep?

So the jugs gunna make it? Not too bad then. Piston is ROUGH! I check my saws often, but gunna check all my saws for tune when I use them from now on too! Its simple and only takes a minute or two and it is worth it. Good luck man!

 

[litefoot]

So altitude and temp are directly proportional. As they go up, a saw will run more rich. As they go down, it will run more lean.

Good lesson, but maybe the greater lesson is to not tune a saw to the ragged edge of performance...then you don't have to worry about temp and altitude so much.

 

[mtngun]

Boy, that wasn't just a little lean, it was way off. Makes you wonder about other things like the quality of pump gas these days.

 

[scootr]

Good article

Here is link to a good article on fuel for saws. I was keeping my fuel in a plastic can, in the back of the truck. Not good, I found another read that said this causes water to accumulate with ethanol fuels. I think it was a combo of bad things.

http://www.madsens1.com/saw fuelmix.htm

 

[constantine]

Here is link to a good article on fuel for saws. I was keeping my fuel in a plastic can, in the back of the truck. Not good, I found another read that said this causes water to accumulate with ethanol fuels. I think it was a combo of bad things.

http://www.madsens1.com/saw fuelmix.htm

Great article! I'm going to get a metal can for my fuel.

 

[blsnelling]

Looks to me like it was just way too lean. Gasoline with ethanol runs fine. It just has to be tuned for it. I'm constantly listening to my saws when working with them.

 

[Evan]

when i saw the pic of the piston the first thought through my head was straight gas

 

[blsnelling]

when i saw the pic of the piston the first thought through my head was straight gas

Well...I suppose it could be. I'm not an expert on reading the difference.

 

[parrisw]

Man that thing is hosed good. I've only seen so far, straight gas do that much of a number on a piston.

 

[volks-man]

scootr:

is that a fairly well blocked filter pictured behind the piston in your post above?

 

[Justsaws]

when i saw the pic of the piston the first thought through my head was straight gas

Gas with zero oil mixed in will usually damage the entire circumference of the piston.

That piston looks as though it was on the edge of lean and then pushed over. Not an un-common results from a saw that is tuned severely lean. The slightest air leak/etc. occurs and damage is accumulated fast and typically not noticed until the saw operator returns the saw to idle or shuts it off and tries to restart.

That piston under went a drastic change in the last moments of its functional life.

 

[mtngun]

Gasoline with ethanol runs fine. It just has to be tuned for it. I'm constantly listening to my saws when working with them.

Ethanol runs fine in saws ? Uh, not really. Boils like crazy in the summer. But what I meant was that the ethanol content of pump gas varies, supposedly it is 10% but there are stories of 18% ethanol. Then there are issues with water absorption and oil separation. If the saw was tuned for 10% and then fueled with 18%, or with watery gas, all bets are off.

Like you, I listen to my saws. I carry a tuning screwdriver in my field kit, and if the saw doesn't sound right or act right, I check the "H" setting. I try to err on the rich side. So far I've been lucky (not counting the 066 that choked on sawdust, or the 064 that spit a circlip ).

 

[Justsaws]

Ethanol does not kill saws, people kill saws.

 

[wigglesworth]

Ethanol does not kill saws, people kill saws.