066 wont start

[Sierra_rider]

A tree removal company just dropped off an 066 to my shop today. Foreman said it would run a few minutes and die. I first removed the bar and chain and then checked the compression using the pull cord (hold and let go). It fell all by itself. Not good, I removed the muffler and checked the rings on the exhaust side. No rings remained in sight, so I removed the cylinder and piston. Top of piston was scorched.
Exhaust side of piston:
View attachment 994697Intake side:
View attachment 994698Even the rings on the intake side are almost frozen, what's left of them. Cylinder was worn really badly up near the top. Likely this engine ran hot and wasn't getting a good fuel mix, perhaps even burning straight gas. It only takes one tank to do it. I have no idea how it would even start and run for a short while. Regardless of cause, this engine needs a whole new top end. Not sure what else could have caused this destruction. Comments and suggestions welcome.

Could be lean, lack of oil, or air leak causing a lean condition. The underside of the piston could tell more of the story.

 

[Mad Professor]

A tree removal company just dropped off an 066 to my shop today. Foreman said it would run a few minutes and die. I first removed the bar and chain and then checked the compression using the pull cord (hold and let go). It fell all by itself. Not good, I removed the muffler and checked the rings on the exhaust side. No rings remained in sight, so I removed the cylinder and piston. Top of piston was scorched.
Exhaust side of piston:
View attachment 994697Intake side:
View attachment 994698Even the rings on the intake side are almost frozen, what's left of them. Cylinder was worn really badly up near the top. Likely this engine ran hot and wasn't getting a good fuel mix, perhaps even burning straight gas. It only takes one tank to do it. I have no idea how it would even start and run for a short while. Regardless of cause, this engine needs a whole new top end. Not sure what else could have caused this destruction. Comments and suggestions welcome.

That will buff right out.........just get a set of rings.

Seriously, was that saw caked up with sawdust/crud too?

 

[Wood Doctor]

No caked up sawdust crud was evident. New piston would be required rather than a set of rings. These worn rings are so frozen on the exhaust side that I would probably find it impossible to remove them. I am a bit worried about the lean running condition. But, that usually requires quite a few hours of operation before a carb running a tad lean produces this much damage. Hi and Lo carb settings were at the recommended level. So, it's a bit strange to say the least.

I personally have never burned out a 2-cycle engine chain saw in all my years, but tree service companies can burn them out in nothing flat. I have other pics of straight-gassed pistons and they look a lot like this one. In those cases the owner usually admitted that he made a mistake and dumped in lawnmower gasoline.

 

[Mad Professor]

No caked up sawdust crud was evident. New piston would be required rather than a set of rings. These worn rings are so frozen on the exhaust side that I would probably find it impossible to remove them. I am a bit worried about the lean running condition. But, that usually requires quite a few hours of operation before a carb running a tad lean produces this much damage. Hi and Lo carb settings were at the recommended level. So, it's a bit strange to say the least.

I personally have never burned out a 2-cycle engine chain saw in all my years, but tree service companies can burn them out in nothing flat. I have other pics of straight-gassed pistons and they look a lot like this one. In those cases the owner usually admitted that he made a mistake and dumped in lawnmower gasoline.

Good luck on trying to save the cylinder. For a customer saw it's not worth your time.

 

[Wood Doctor]

Good luck on trying to save the cylinder. For a customer saw it's not worth your time.

I also decided to trash this cylinder. Yes, I agree, it is not worth my time. I have an unused cylinder in stock, and I will try to use it with a new piston, rings, etc. However, my experience has been that the complete P/C kit is usually more successful.

 

[Mad Professor]

I also decided to trash this cylinder. Yes, I agree, it is not worth my time. I have an unused cylinder in stock, and I will try to use it with a new piston, rings, etc. However, my experience has been that the complete P/C kit is usually more successful.

I have put new $tihl P/C kits on my own saws. I'm real carefulabout taking care of those.

I also learned the skill of takin transfer off and making a free Stihl a great runner again, but for me, no profit in it.

$tihl i$ real proud of their part$, but they are quality, at least the NOS OEM.

 

[Sierra_rider]

No caked up sawdust crud was evident. New piston would be required rather than a set of rings. These worn rings are so frozen on the exhaust side that I would probably find it impossible to remove them. I am a bit worried about the lean running condition. But, that usually requires quite a few hours of operation before a carb running a tad lean produces this much damage. Hi and Lo carb settings were at the recommended level. So, it's a bit strange to say the least.

I personally have never burned out a 2-cycle engine chain saw in all my years, but tree service companies can burn them out in nothing flat. I have other pics of straight-gassed pistons and they look a lot like this one. In those cases the owner usually admitted that he made a mistake and dumped in lawnmower gasoline.

I'm the only running my saws, so mine never have catastrophic failures. However, my tree biz buddies, that do it full time, are always burning up saws. The common denominator with all of them is their employees fueled the saw that burnt up. If had employees, I think I'd be in charge of of mixing fuel and fueling up saws lol...

 

[Maintenance supervisor]

I often stop by my local Mom&Pop saw shop for parts and such. A few weeks ago a teen/20 something carried in a mangled MS500i that had crush damage.
His " boss" bought the saw for him to do work clearing property, no safety gear and cheap labour = broke equipment.
People bit@h about cheap knock off saws but cheap uneducated labour probably leads to 90% of saw failures, investing in a well trained employee pays for itself in very short time.

 

[TheRockyMountainKing]

I have yet to try leak/vac test, but it has strong spark, great compression, and its getting fuel, can the flywheel be 180 degrees out of time?

 

[Mad Professor]

I have yet to try leak/vac test, but it has strong spark, great compression, and its getting fuel, can the flywheel be 180 degrees out of time?

Is flywheel key there? It's not a 4-stroke.

 

[Bob Hedgecutter]

I have yet to try leak/vac test, but it has strong spark, great compression, and its getting fuel, can the flywheel be 180 degrees out of time?

Only if it has two cut keyways at 180 degrees from each other and the key is in place.

 

[TheRockyMountainKing]

Yeah ok, dumb question. The flywheel key is there. Im no sure what to try next

 

[Bob Hedgecutter]

Yeah ok, dumb question. The flywheel key is there. Im no sure what to try next

Not too dumb at all- there are 1122 flywheels with two keyways cut into them so they can be used with limited or unlimited coils, depending on which keyway is used. They are not 180 degrees different though and if you pick the wrong keyway for the coil- trying to start the saw will usually let you know you got it wrong.

You say the saw is getting fuel- is it eventually leaking out the muffler after 20-30 rope pulls?

Someone else said it earlier- compression, spark, correct fuel/oil/air mix all coming together in the right area at the right time- thats all it takes and some or one of those is not happening properly on your saw.

Someone else asked you for compression test numbers and report back.

Several others have suggested a pressure and vacuum test post topend renewal.

That gives you some idea of "what to check next"

You have tried a new spark plug eh? Would not be the first time a plug sparked out of the cylinder and earthed- but does not when under compression.

 

[TheRockyMountainKing]

Not too dumb at all- there are 1122 flywheels with two keyways cut into them so they can be used with limited or unlimited coils, depending on which keyway is used. They are not 180 degrees different though and if you pick the wrong keyway for the coil- trying to start the saw will usually let you know you got it wrong.

You say the saw is getting fuel- is it eventually leaking out the muffler after 20-30 rope pulls?

Someone else said it earlier- compression, spark, correct fuel/oil/air mix all coming together in the right area at the right time- thats all it takes and some or one of those is not happening properly on your saw.

Someone else asked you for compression test numbers and report back.

Several others have suggested a pressure and vacuum test post topend renewal.

That gives you some idea of "what to check next"

You have tried a new spark plug eh? Would not be the first time a plug sparked out of the cylinder and earthed- but does not when under compression.

Yes, gas does leak out of the muffler. I have no way to compression test or vac test.

What would cause the plug to lose spark under compression.

 

[Bob Hedgecutter]

Yes, gas does leak out of the muffler. I have no way to compression test or vac test.

What would cause the plug to lose spark under compression.

But you said it failed a test pre teardown and repair?

A faulty spark plug causes that.

Id say a set of crank oil seals might help your cause a long way then. If it is sucking air bad at the seals- it might not fire up. And you said earlier the seals are old.

 

[TheRockyMountainKing]

Can you show us a photo of the worn out rings that failed?
Worn ring usually just = new rings and good to go- you replaced the entire top end, which in turn leads to thinking the top end was roached from an air leak (failed leak down test, seals are old).

Recent carb rebuild- download an 066 IPL and check the carb is assembled correctly.
If it is starved for fuel and not flooding- for some reason the fuel is not reaching the combustion chamber- could be the impulse line is incorrectly or loose fitting and not pulsing the pump diaphragm, was it an OEM replacement line- or fleabay cheapie? Impulse could be blocked. Or the carb assembled incorrectly.
Either way, if it pops, it should run if fuel was dribbled into the carb throat with the choke off, choke moved to "on" and the rope pulled.

I wasnt sure why it failed the leak test, i know it has compression though. My hand is chewed to **** after pulling it so much. I used a genuine stihl carb kit, genuine impulse and fuel lines. I assembled it exactly like it came apart. Impulse is not plugged off for certain.

 

[TheRockyMountainKing]

But you said it failed a test pre teardown and repair?

A faulty spark plug causes that.

Id say a set of crank oil seals might help your cause a long way then. If it is sucking air bad at the seals- it might not fire up. And you said earlier the seals are old.

It did fail a test pre repair, uncles friend or logger buddy did it before i got the saw. Should have clarified that sorry.

Tried old and new plugs, no bueno.

I have a set of seals, ill put them in and try.

 

[Bob Hedgecutter]

I wasnt sure why it failed the leak test, i know it has compression though. My hand is chewed to **** after pulling it so much. I used a genuine stihl carb kit, genuine impulse and fuel lines. I assembled it exactly like it came apart. Impulse is not plugged off for certain.

Well if you are convinced everything is 100%- take it to a shop, get them to compression test it- pressure and vac test it and come back with the results.
Might cost you a few $ but at the moment it is only a door stop not a saw.

 

[TheRockyMountainKing]

Well if you are convinced everything is 100%- take it to a shop, get them to compression test it- pressure and vac test it and come back with the results.
Might cost you a few $ but at the moment it is only a door stop not a saw.

Ill try crank seals first. Labor at the local shop is $$$

 

[lone wolf]

Ill try crank seals first. Labor at the local shop is $$$

You should not assume the carb is good just because you worked on it. What is the history of the saw, the cyl and piston was destroyed? If so what did the piston look like,was one side or both sides scored up? This could help troubleshoot the initial cause whether it was from a possible vac leak or if it was straight gassed.