266 Scored Piston

[Wildwinger]

Here's the piston from exhaust side..

my dad gave me this saw, it's a 1983. We replaced the carb, retuned it (by his ear) and ran a couple tanks through it

This saw has been used with 32:1 mix all it's life. Pretty much just a firewood saw (8-12 cord/year). I doubt it's ever been cleaned thoroughly (I try to blow everything out with compressed air after I cut but I know it didn't always get that…and there's a bit of gunk on the fins/everywhere)

No compression gauge, but it does fall when held by starter. Not straight down, but it doesn't stay up for more than a second. A couple pauses on the way down.

I'm pretty new to engine work: does this look like it's caused by carbon buildup? I can see three little pieces that could make their way into the cylinder, who knows how many already did

Also, there was an amount of fine dust on the carb inlet throat, I replaced the air filter (mesh) with another mesh one and didn't see an improvement. Would dust do something like this?

Anyway, seems like a good excuse to make myself a 272...

 

[High-Wall]

Check your cyl. - if it isn't scored I would put a meteor piston in it. If cyl. won't clean up go the 272 route. Keep fan and fins clean, 266's live longer when cool. Carbon concern will prolly go away w/ 40-1 Stihl Ultra mix. '83 model may have the smaller tillotson. I hope you need a new crank rope after the rebuild!

 

[drf255]

Does the saw run? Were you just interested so you pulled that muffler?

That piston isn't that bad looking. I'd wanna see pics when out. It still may be usable with a new ring and some slight polishing. Gotta see when it's apart.

 

[jughead500]

Doesn't look like the ring has been hurt.i believe that is just carbon smearing.
I would take the top end off,decarbonize,polish,rering etc.

 

[Wildwinger]

The saw starts and runs fine, but pulls quite easily which is why I checked

I'll pull it apart tonight, thanks for looking!!

 

[nmurph]

Doesn't look like the ring has been hurt.i believe that is just carbon smearing.
I would take the top end off,decarbonize,polish,rering etc.

This!

 

[jughead500]

This!

Also take a little time after decarbonizing and polish that exhaust port for good measure.kinda helps with future build up along with good oil.

 

[SawTroll]

my dad gave me this saw, it's a 1983. We replaced the carb, retuned it (by his ear) and ran a couple tanks through it

This saw has been used with 32:1 mix all it's life. ....

A steady diet of 32:1, maybe with inferior quality oil, may well be the culprit.

What carb model is the replacement carb?

 

[SawTroll]

Check your cyl. - if it isn't scored I would put a meteor piston in it. If cyl. won't clean up go the 272 route. Keep fan and fins clean, 266's live longer when cool. Carbon concern will prolly go away w/ 40-1 Stihl Ultra mix. '83 model may have the smaller tillotson. I hope you need a new crank rope after the rebuild!

Yes, either HS-163 or an equally small Walbro.

 

[Flat47]

That's not scored. Put a new ring in it and run it for another 30 years.

 

[Big_Wood]

i'd clean it up and run it with all the original parts. you run that ring or a new one and i bet the compression doesn't change at all. that ring is already broken into the cylinder walls.

 

[Wildwinger]

I think the

Yes, either HS-163 or an equally small Walbro.

I think it's the HS-163A but I'm not sure. Here's the new one:




And the old. They're different but they seem to be the same size from what I can tell, but I can't tell very much!

 

[burnses]

I wouldn't lose too much sleep over that one...what made ya pull the muffler....down on power....

 

[Wildwinger]

I wouldn't lose too much sleep over that one...what made ya pull the muffler....down on power....

Low compression based on a starter rope test, the saw cuts like a boss

 

[nmurph]

That's why the starter rope test is worthless. Variables such as saw weight, amount of rope on starter, size of rope on starter, size of rotor, time since saw was last run (and others I'm sure I'm forgetting), can affect the validity of this test. I can tell a good bit by just turning the motor over slowly with the starter and feeling compression and let-off.

 

[jughead500]

That's why the starter rope test is worthless. Variables such as saw weight, amount of rope on starter, size of rope on starter, size of rotor, time since saw was last run (and others I'm sure I'm forgetting), can affect the validity of this test. I can tell a good bit by just turning the motor over slowly with the starter and feeling compression and let-off.

Yeap what neal said.

 

[drf255]

Low compression based on a starter rope test, the saw cuts like a boss

Then clean that giant chunk of carbon out of it with the piston all the way up and run the saw.

Unless you're looking to mess with a perfectly fine saw for performance gains (which I needlessly do all the time), leave it be.

 

[Wildwinger]

So - a long overdue update


Finally got around to checking the compression. Using a super old gauge (that read 150psi on my 246 and 044, so I'd say it's sort of accurate) I pulled 180+psi on the old 266.

No wonder it cuts like a boss...

 

[kz1000]

That sucks! I would box it up and send it my way before your dad sees it in that condition.