Stihl 066 Operator Said, "It Stopped Dead."

[redtractor]

Wood Doctor, OP, any damage to piston or obvious seize situation gets a pressure/vac test before it's torn down. That eliminates a large chunk of guess work and shines a light on the little gremlins that may otherwise go unnoticed.

Backyard Lumberjack, these are WOT type of machines. They do their best work & best cooling like that and you are doing them a favor by treating them so. Had a cust tell us he only ran his mowers an hour at a time so they wouldn't become overheated. It seemed logical to him. We explained otherwise. I don't think he believed us.

edit.. Don't mean anything with the blue print. Must've hit a wrong button and can't correct it.

 

[Brush Ape]

Don't take pictures with a potato.

 

[Deets066]

lesson to be learned here...

since too lean is detrimental to chainsaw piston life... maybe check that H setting more often. each tank full, at least the slot's position? the mixture adjustments can vibrate inward... my 019T started acting like an unfriendly cousin... I wasn't happy! so, started the research... finally got into the LA, L and H... etc... tweaked the L and the LA... and got it back on course... then H. now once running will sit there and idle with chain just creeping... pop-pop-pop! with an "Let's get this show on the road!" attitude... and throttle response is crisp up to cutting rpm... each to his own, but I never run my saws on a steady WOT when cutting... oh sure WOT but I momentarily lighten cutting load and back off, just to change rpm, let piston cool bit, cyl oil up, skirts oil up... then back to work... etc. I was taught this procedure by my Dad at a young age... he was a well-trained very experience engine mechanic... A&P type... and was an air-cooled engine specialist... very mechanically inclined! not saying it's gospel, just sharing what I do.

darn!, guess I will loose the chainsaw race! lol

too lean hurts: I picked up my 044 from an owner/operator/arborist... used it every day. day after day! over two years he owned it! ran fine. one day all day, fine. next morning on the job 15 mins and stopped. had no idea what was wrong with it, and sold it. I got it next day still with full tanks of fresh fuel and oil for chain/bar... back at shop, when I got the muffler off, i could see he had scored bad the piston exh side and stuck the rings hard! that saw had had it. lol... no doubt he had not checked H lately, and it leaned out on him and in the excitement and noise of running hard... Murphy showed up! as I got into it, was relieved the cyl looked very serviceable once cleaned up... speaks very well for Nikasil - but alas, not so the piston and rings!

this 044 piston has seen better days!

View attachment 10878

rings on exh side stuck hard!

View attachment 10879

intake side; rings still loose in lands...

View attachment 10880

and the winner is!:

View attachment 10881

Letting off the throttle will not cool anything, air cooled two strokes can be cooled by "air" from the flywheel cooling fins. The faster they are spinning the more cooling. The piston is cooled by the fuel oil mix. You get the most fuel oil mix at WOT. For you want more cooling after a long cut blip the throttle to WOT in a few short bursts.

Not trying to discredit anything your dad taught you, but this is what I've been taught and what I believe

 

[Deets066]

To me it isn't necessary to check the screw locations. You should be able to tell plain as day if it starts to run lean.

 

[Wood Doctor]

I have a couple of other ideas to consider. The fuel tank is about half full. There is so much damage from heat that it's amazing to me that the engine even started and then ran a half tank of fuel out. My experience has been that a lean mixture from the carb usually requires several tanks of fuel before it can cause this much damage, but a straight gassing can do it in a tank or less. Therefore, is it possible this was both a lean mixture supplied by the carb AND a straight gas at the same time, both producing enormous heat that fried the rings, piston, and cylinder?

I recall reading somewhere that you can check the fuel to see if any oil mixture is present. Can you advise me on this procedure? That way we can at least determine if the gas is straight or was mixed OK. TIA.

 

[Moparmyway]

Fastest way to cool down an OPE 2 stroke is to hold WOT unloaded for a few seconds, then shut off the saw while holding the throttle WOT.

 

[TJ the Chainsaw Mechanic]

I'm going with to lean a mixture on the 2 stroke oil. Usually 1 tank of straight gas does enough damage to seize up. Unless these jugs are stinkin tough.

 

[Nitroman]

Stick your finger into the gas tank and pull it out and see if it is slippery once it evaporates.

 

[Fifelaker]

I check fuel by dipping a finger in it, then rub it against my thumb. Mixed gas will be smooth, straight gas will feel gritty. You cannot tell what ratio, but you can tell if it has oil in it.

 

[Wood Doctor]

OK, I did the "slippery finger" test. The fuel in the 066 tank appears mixed based on that alone. Second, I checked the color of the 066 tank fuel against my personal mixed fuel. Both were the same green color. In addition, my can of straight gas that I poured into another jar is almost clear. So, it looks like the half tank of fuel remaining in the 066 tank was mixed OK and only a little more cloudy than my mixed fuel.

This experiment at least reveals that the damage over time was not cause by running straight gas, unless it was done on an earlier tank of fuel. Most likely, the lean mixture from the carb caused it all, building up over time. It is amazing to me that this operator was even able to start and run this engine through a half tank of mixed fuel.

My thanks to all who have responded to this thread thus far.

 

[redtractor]

The carb has these plastic limiters on it, so it's possible that the setscrew was not all the way closed.

Regardless, that worries me. I'm ready to pull out that limiter. These things drive me bonkers.

The limiter not letting the needle be closed all the way is why I'm thinking more like an air leak.

I found out that once I got hooked on tuning these carbs for myself, the only good limiter was a disabled limiter!

 

[Wood Doctor]

It's time for some good news. I installed the new top end and the engine is running once again. I discovered another flaw that could have stopped the saw dead. There was no spark. I tried three plugs and none worked. So, I removed the ignition module, cleaned it up, and reset the gap at 0.011". The spark came to life immediately using any of the plugs that I had tried before.

Compression measures 165 psi on a warm engine. Idle is steady, acceleration is smooth. I backed the hi-speed set screw 3/4 turn out. All systems are go and ready for initial break in period.

 

[Backyard Lumberjack]

I have a couple of other ideas to consider. The fuel tank is about half full. There is so much damage from heat that it's amazing to me that the engine even started and then ran a half tank of fuel out. My experience has been that a lean mixture from the carb usually requires several tanks of fuel before it can cause this much damage, but a straight gassing can do it in a tank or less. Therefore, is it possible this was both a lean mixture supplied by the carb AND a straight gas at the same time, both producing enormous heat that fried the rings, piston, and cylinder?

I recall reading somewhere that you can check the fuel to see if any oil mixture is present. Can you advise me on this procedure? That way we can at least determine if the gas is straight or was mixed OK. TIA.

in reading this thread on this saw's demise... I am a bit confused on how a H screw could or would go to full closed. especially since it has a spring on the needle. since I don't run my saws WOT in neutral, well other than tuning... lol... maybe someone can tell me. if u have a big saw like that, and you are cutting wood... and u start to the close H... will it keep running until fully closed? or as the needle gets turn in, or vibrates in (doubt that) will the saw keep running, then quit before once fully closed? me, personally, I don't think the damage took place over 3-4 tanks... I don't think a chainsaw will run very long with an infinity to one air/fuel ration... one being the fuel...

I think there may be facts not disclosed. how long did it run before quit? first run of day? anybody have access to it, sabotage? I know as a rule, I don't ck my carb's setting... so if closed how would one know, if not ckd... until the damage had taken place? don't think they could have... other than by sound... but if they could not 'read' the sound... no need to think otherwise... just like my arborist pal who stuck the 044's rings...

 

[Backyard Lumberjack]

Wood Doctor, OP, any damage to piston or obvious seize situation gets a pressure/vac test before it's torn down. That eliminates a large chunk of guess work and shines a light on the little gremlins that may otherwise go unnoticed.

Backyard Lumberjack, these are WOT type of machines. They do their best work & best cooling like that and you are doing them a favor by treating them so. Had a cust tell us he only ran his mowers an hour at a time so they wouldn't become overheated. It seemed logical to him. We explained otherwise. I don't think he believed us.

edit.. Don't mean anything with the blue print. Must've hit a wrong button and can't correct it.

blue, red, or purple... font color don't bother me... but why can't you correct it? u have Edit at bottom of post. and a font color's change is ez, unless on fone and app wont allow. but any color is ok by me, even though black is the rule of thumb...

 

[redtractor]

I tried highlighting the whole phrase, then found the menu item above for color but nothing helped. My computer at home is going downhill so that may be it. I get downtime at work and they have folks fix theirs so its more reliable. And using their data package saves more for me at home.

 

[Backyard Lumberjack]

r

Letting off the throttle will not cool anything, air cooled two strokes can be cooled by "air" from the flywheel cooling fins. The faster they are spinning the more cooling. The piston is cooled by the fuel oil mix. You get the most fuel oil mix at WOT. For you want more cooling after a long cut blip the throttle to WOT in a few short bursts. Not trying to discredit anything your dad taught you, but this is what I've been taught and what I believe

oh you are not. but thanks for the clarification. I certainly agree with you that there is a lot of air that moves off the flywheel's fan blades spinning... faster it spins higher the cfm... however the heat the piston and rings are absorbing from direct contact with the combustion process is incredible. not sure what is more beneficial the cooling fins on cyl or flywheel... I do know an air-cooled aircraft engine has no flywheel cooling each cylinder, although it does have an airstream once in air and some effect off prop, but at hub of prop & 1/3 up while taxiing not much... ... and at WOT there is an incredible amount of heat taxing the 50:1 ratio (or whatever u run at) lubrication process. speaking of taxes, its kinda like this to me:

Joe Blough just got back from his taxman's office... and says... wow...my taxman really got me some good tax savings on my return. well, in the land of federal taxation returns... the tax savings never equates to the cash flow required to obtain them. at the cost of WOT cooling, a lot of heat is produced.

I do enjoy reading other's comments and ways of doing things especially when it comes to engines. one poster's ideal cooling technique is run saw WOT, then turn OFF for ideal cooling. you know what is going to freeze over first... before I choose that method. not saying his method is not ok, right or preferred. just not in my camp... I always set my saws down after cutting... and let them idle some... let them cast off their heat in a swirling bath of cool air flow for slower running clearance changes. in 2-stroke aircraft engines... often as not... pilots will get to the holdshort line, do a run up, and note: "all gauges in GREEN!"... and off they go... only to have an engine out at 1100' on departure... needles in green vs full heat soak are not the same condition. as you all know alum and iron expand at dif rates...

all I know is that after almost 20 years use of my saws, all stihl running strong, no scored pistons! oh... and one echo!

imo... fun stuff all this is, no doubt a swell clan of wood cutters and smart engine people, too!

 

[Wood Doctor]

in reading this thread on this saw's demise... I am a bit confused on how a H screw could or would go to full closed. especially since it has a spring on the needle. since I don't run my saws WOT in neutral, well other than tuning... lol... maybe someone can tell me. if u have a big saw like that, and you are cutting wood... and u start to the close H... will it keep running until fully closed? or as the needle gets turn in, or vibrates in (doubt that) will the saw keep running, then quit before once fully closed? me, personally, I don't think the damage took place over 3-4 tanks... I don't think a chainsaw will run very long with an infinity to one air/fuel ration... one being the fuel...

I think there may be facts not disclosed. how long did it run before quit? first run of day? anybody have access to it, sabotage? I know as a rule, I don't ck my carb's setting... so if closed how would one know, if not ckd... until the damage had taken place? don't think they could have... other than by sound... but if they could not 'read' the sound... no need to think otherwise... just like my arborist pal who stuck the 044's rings...

As for the fully closed hi-speed set screw, that can vary from one saw to the next. My MS361 will not run long if fully closed and it has no plastic limiters. This saw has them, and I have to think that the limit switch would prevent a full closure, but it did allow for excessively lean running.

I also agree that it could have been tampered with and sabotaged. This saw is used at a sawmill and is somewhat unrestricted. I believe it was the first run of the day, but I will find out for sure. What I will tell the operator is that he has to start being careful about where he stores this saw.

Perhaps the biggest mystery I have now is why the spark shut down also when the fried piston locked up. That's a chicken vs. the egg problem. Which came first? Usually a failing ignition module quits slowly, kind of like a sputtering engine running out of fuel. This one quit delivering a spark but only needed a regap and is now back in business.

 

[Moparmyway]

Fastest way to cool down an OPE 2 stroke is to hold WOT unloaded for a few seconds, then shut off the saw while holding the throttle WOT.

one poster's ideal cooling technique is run saw WOT, then turn OFF for ideal cooling. you know what is going to freeze over first... before I choose that method. not saying his method is not ok, right or preferred.

Big difference between "fastest" and "ideal"

When you jump to conclusions, the landings can get rough

 

[jmssaws]

To me it isn't necessary to check the screw locations. You should be able to tell plain as day if it starts to run lean.

Indeed.
A saw needs tuned every day and you should know by the sound that it does

 

[Moparmyway]

To me it isn't necessary to check the screw locations. You should be able to tell plain as day if it starts to run lean.

Indeed.
A saw needs tuned every day and you should know by the sound that it does

In the first minute or so of warming up I can tell if any of mine need adjusting, and I can hear as well as feel a difference as the day warms up, the saws are allways getting adjusted