Ms660 compression?

[300zx_tt]

I've had my 660 for about a year and a half now and it's been awesome. Bought it used from a big tree service. It ran very well, compression was about 155psi if I remember correctly, it was definitely higher than 150psi. Fast forward to last weekend, I was milling a 32" white oak that's 13' long. Saw was bogging down when it wouldn't normally. I used to be able to let it idle in the cut for 10 minutes if I wanted to, it shut off within 20 seconds when I tried to let it idle on Saturday. Everything was the same, same bar oil same 2 stroke oil same mix ratio, the only thing I changed was I got gas at gulf instead of at Sunoco where I normally get it. The saw was just off, so I backed it out of the cut, brought it home and compression tested it. It wasn't hot when I tested it and read 105psi. I took the muffler off and looked inside, I can see what I'd describe as light gouges on the exhaust side of the piston, and 2 light scores on the back of the cylinder wall .

Now my questions:
- what could have caused the scoring I have?
-How bad does the scoring have to be to affect the compression?
- does low compression cause the issues I'm having?
- where's the best place to buy parts?
- do I need any specialized tools to replace the cylinder, piston and rings?

Also if anyone has pictures of their piston and cylinder they'd like to share that would be awesome.

 

[s sidewall]

Don't know much about Stihl but sounds like you got a vacuum leak somewhere that caused a lean condition to take out the piston.

Steve

 

[s sidewall]

And yes you will have low compression for your piston being scored up, possibly transferred aluminum to cylinder.

Steve

 

[blsnelling]

To little oil and too lean of a tune for milling. You should be running at least 32:1 and you'll have to remove the limiting cap on the carb needles and tune it richer.

 

[ironman_gq]

Milling is about as hard on a saw as things can get, long hot pulls at full throttle under high load makes for a lot of heat. To combat the heat and make the saw stay alive you use more oil and tune them a little richer. Extra fuel helps pull heat out of the cylinder and more importantly it insulates the top of the piston. Sounds like you got hot and might have had some piston to cylinder rubbing and maybe some aluminum transfer.

 

[rupedoggy]

You cooked it

 

[s sidewall]

To bad no one makes a water cooled cylinder kit for milling.

Steve

 

[ironman_gq]

Now that would be something for someone to look into making!

 

[300zx_tt]

Milling is about as hard on a saw as things can get, long hot pulls at full throttle under high load makes for a lot of heat. To combat the heat and make the saw stay alive you use more oil and tune them a little richer. Extra fuel helps pull heat out of the cylinder and more importantly it insulates the top of the piston. Sounds like you got hot and might have had some piston to cylinder rubbing and maybe some aluminum transfer.

To little oil and too lean of a tune for milling. You should be running at least 32:1 and you'll have to remove the limiting cap on the carb needles and tune it richer.

I run 30:1 and I took it to my loacal dealer to have the carb tuned to run 30:1. Only use stihl hp ultra 2 stroke oil.

 

[blsnelling]

You need a much richer tune than normal for milling.

 

[300zx_tt]

You need a much richer tune than normal for milling.

I had the carb tuned for milling, specifically to run 30:1 mix and to mill.

 

[rupedoggy]

Maybe Sonoco has no alcohol but the other does. Any alcohol dilutes the settings and needs re-adjustment. Compared to Gasoline, Alcohol takes twice as much in an engine for proper adjustment if each is run straight.

 

[pioneerguy600]

Its cooked, have it pressure and vac tested first before removing the cylinder. Most likely cause though was improper fuel mix ratio or tuned too lean for milling no matter what the dealer set it at the damage is done.

 

[CR888]

I think learning to tune a saw well has more benefits that just having a crisp nice running saw. It teaches you to early detect a lean condition, also to know what's appropriately rich for milling. When milling it only takes a poor shake of the gas can, a change in conditions to put you on a bad path. Hopefully it will only cost you a sore finger from rubbing wet&dry sandpaper and a set of rings to get you up & running. I'd do it yourself with the aid of the forum. A dealer don't like removing transfer and are more into replacing parts which will most likely be a piston/cylinder kit + labor. Costly to say the least. If your gonna mill you may as well start learning this chainsaw stuff.

 

[drf255]

Pull jug and report back.

I run 24:1 to mill and make sure there’s still some burble in cut.

 

[JTM]

I had the carb tuned for milling, specifically to run 30:1 mix and to mill.

What was the temperature in the shop when he tuned it and what was the temperature outside when you were milling?

 

[300zx_tt]

I think learning to tune a saw well has more benefits that just having a crisp nice running saw. It teaches you to early detect a lean condition, also to know what's appropriately rich for milling. When milling it only takes a poor shake of the gas can, a change in conditions to put you on a bad path. Hopefully it will only cost you a sore finger from rubbing wet&dry sandpaper and a set of rings to get you up & running. I'd do it yourself with the aid of the forum. A dealer don't like removing transfer and are more into replacing parts which will most likely be a piston/cylinder kit + labor. Costly to say the least. If your gonna mill you may as well start learning this chainsaw stuff.

I'm on this site to learn, I'm young and I have a limited amount of knowledge. I'll be the first to admit that. After reading posts here is when I decided to buy an ms660 and start milling, instead of hacking everything up for firewood. Before I milled I took it to a local reputable shop and had the carb tuned. Told him what I was doing and he said he'd take care of me. I've since found a better shop a little farther away but it's worth the drive.

What was the temperature in the shop when he tuned it and what was the temperature outside when you were milling?

I got the saw and had the carb work done in February, so 45-50 in the shop vs last weekend in 85 and full sun.

I usually tend to hang out in the milling and firewood sections of this forum, clearly I should have been in here researching. I'm beating myself up because I THOUGHT I was doing everything right, turns out I wasn't! Bummer!

 

[rupedoggy]

Education sometimes costs

 

[Tin-knocker]

The best way to learn is by making mistakes. Find the cause and make sure it doesn't happen twice!
+1 on vac testing and leak down testing. Better to double check before you start tearing things apart.

 

[Canyon Angler]

What was the temperature in the shop when he tuned it and what was the temperature outside when you were milling?

Just out of curiosity, as the air temperature goes up, would you usually want to richen, or lean out, the mixture?

On one hand, as the temperature goes up, the amount of oxygen in a given volume of air decreases, so that suggests to me that you would want to lean the carb ... but fuel also cools the engine, and cooling becomes more critical as the temperature goes up, so I'm not sure...my hunch says, "As temp increases, richen the carb." So which is it?

Just trying to learn here. I've always had my saw guy set and check my tuning, but I want to learn to do it myself better.