thoughts on my 066

[TJ-Bill]

I was using it this past weekend and it seemed sluggish I had the 26" bar is some 24" maple and it just didn't seem happy. About 1 hr into cutting it died and it didn't sound right when it quit.. I knew it was full of fuel and clean air filter so I put it away and grabbed another saw. To night I started it up and it ran ok but not great, I checked the carb tuning and it seemed good (I'm far from an expert). I put the comp tester on it and I'm getting about 125psi. I pulled the muffler and looked at the piston and found this..

the dark spot on the right is a discoloration not a shadow. You can see it start at the top of the piston.:msp_unsure:

 

[mdavlee]

Time for a pressure/vac test and a new piston looks like. Was it lean on the tune maybe?

 

[medic8852]

That looks almost identical to the 066 i bought that was blown. It pushed about 115 on the tester. Never even tried to fire it, carb needed help and the fuel line was cracked. Ended up with a piston from northwoods saw, a sponser on here, a little time with some muriatic acid, and it runs great now. Ran it with a 28" and rsc on a 40" diameter oak today and it was scary fun. View attachment 260473

 

[cutforfun]

I may be way off but it looks like carbon build up may be part of the problem

 

[shawn022]

What the history on the saw? That scoring looks "old" to me. Maybe it was cleaned up and sold? The reason I say that is because it looks like the ring groove has been opened up where the scoring is.

 

[procarbine2k1]

What the history on the saw? That scoring looks "old" to me. Maybe it was cleaned up and sold? The reason I say that is because it looks like the ring groove has been opened up where the scoring is.

Yes it does, good eye.

 

[fearofpavement]

Whooeee. That baby got hot. Looks like some detonation going on there from the way the piston is pitted and discolored. How does your plug look?

 

[Anthony_Va.]

I'd change the mix I was using before also. Thats a whole lotta carbon buildup. I'd say the cylinder would clean up from the looks of the piston but thats just a guess.

I think it must have been ran too lean. Maybe the carbon buildup could have had something to do with it?

 

[TJ-Bill]

What the history on the saw? That scoring looks "old" to me. Maybe it was cleaned up and sold? The reason I say that is because it looks like the ring groove has been opened up where the scoring is.

That's a good possibility. My cousin Bought the saw used on Ebay. He had no idea what he was buying and never used it because it was to big so I traded for a MS180 and some Jeep parts!

Whooeee. That baby got hot. Looks like some detonation going on there from the way the piston is pitted and discolored. How does your plug look?

Plugged looked ok. nice and brown.

 

[TJ-Bill]

BIGBORE CYLINDER PISTON FITS STIHL 066 650 660 MS650 MS660 CHAINSAW | eBay

 

[064AV]

Hey medic8852...
That orange cover on the starter in your pic is only supposed to be on when temperatures are below something like 15 degrees Fahrenheit. It reduces the airflow available to cool the cylinder. P&C get too hot, and there'll be seizure.