Damaging Pistons and Cylinders on 660s

[ericjeeper]

Thanks Eric, I'll have to check my other saws so see what you are talking about but with the saw being cooled off it is a dark brown almost black color.

But if the saw was ran at an idle for very long the plug was last seeing a different fuel to air mixture at that time.

 

[Tree Student]

What are these saws taching out at? Probably set 'em around 12.5k rpm for the knuckle-dragging crowd, 13.5k for the folks who know what they're doing.

What are you using for fuel and premix oil? Who mixes the gas?

Clearly someone is doing something wrong.

There have not been any changes on these two saws that I know of, when I bought them new I took them to the local stihl dealer who has been working on them for 25+ yrs and had them checked out. I never thought to ask about the rpm's.

I am using regular unleaded gas with stihl 2 cycle from the saw shop, one gallon plastic gas can to one small bottle of oil for a gallon mix. I usually mix the gas but have taught my foreman how to mix also so we are the only two.

You're right, there's something wrong and I'm hoping that I'll find a clue here.

 

[Tree Student]

But if the saw was ran at an idle for very long the plug was last seeing a different fuel to air mixture at that time.

When that saw stopped it had been running full throttle cutting firewood for a couple of hours, he let off the trigger to reposition for the next cut and the saw died. Now it's on the shop bench torn apart.

 

[Mad Professor]

There was a report on another site that some batches of "10% ethanol" gas was tested/analyzed and found to have greater than 25% ethanol. That would cook most two strokes unless you had a lot more oil in the mix.

I filled two 55-gal drums with pump premium before the switch to corn fed and am about out of the good stuff. I don't use that much fuel so next time I'm filling up the drums at the airport. If I pay $1.50 more a gallon I'm still ahead if it avoids cooking just one saw. Another plus is the mix and the raw gas itself has a longer shelf life.

If I can sneak some samples in at work I'll try to check some of the local corn fed for alcohol content.

 

[Lakeside53]

If you are using Alcohol containing gas, you will need to re-adjust the H screw richer, which means pulling the limiter cap on the 660. The 066 may not have a limiter cap which makes for easy adjustment.

Since Jan 2007 (?) new Stihl OPE has been adjusted at the factory for 10% ethanol.

 

[Lakeside53]

There was a report on another site that some batches of "10% ethanol" gas was tested/analyzed and found to have greater than 25% ethanol. That would cook most two strokes unless you had a lot more oil in the mix.

Was this a verifiable report or hearsay? I've not heard of anything like this out here.

10% isn't an issue in saws. 25%? That would be a problem.

 

[bcorradi]

What other saws are you running in your fleet that came out unschathed?


If all the saws are serviced and tached at the same shop I find it hard to believe gas being the source of the problem considering all of the other saws are working fine and supposedly running the same gas. If they all pressure tested fine I would have to think either someone made carb adjustments (probably unlikely) on them after comming back from the shop or someone snuck in some straight gas on those 066/660's with malicious intent. Something just doesn't add up imo.

 

[Ray Bennett]

I usually mix the gas but have taught my foreman how to mix also so we are the only two

That may be your problem. I would never trust anyone to mix my gas but me or an experienced saw man with his own equipment. Is there still gas in the saw from the day it blew? That could be your clue. If that is not it did the saws blow up on the same guy? If he is running them hard till they shut off from lack of fuel that will really lean them out as well. It sounds like you have eliminated every thing but user error. I always say "My equipment never breaks when I use it"

 

[Tree Student]

What other saws are you running in your fleet that came out unschathed?


If all the saws are serviced and tached at the same shop I find it hard to believe gas being the source of the problem considering all of the other saws are working fine and supposedly running the same gas. If they all pressure tested fine I would have to think either someone made carb adjustments (probably unlikely) on them after comming back from the shop or someone snuck in some straight gas on those 066/660's with malicious intent. Something just doesn't add up imo.

I've been running an echo CS-300, Stilh 290, 066, and 660 on the same jobs with the same gas can and crew. All of my equipment stays under lock and key when I'm not around unless the foreman is running the crew so malicious intent is not one of the causes that I am considering.

Could use and vibration lead to the carb adjustments moving slightly?

Here are the pics.

 

[bcorradi]

Did you just take those pics? If so, you should go back out there and wind in the high jet (clockwise) on the 066 while counting the turns and then back it out to its original position. Report back on where it is set at.

Vibration may cause them to wind themselves out (making them richer, but thats rare), but not wind themselves in.

 

[Mad Professor]

Was this a verifiable report or hearsay? I've not heard of anything like this out here.

10% isn't an issue in saws. 25%? That would be a problem.

Not sure how reliable the post was on another forum, but as you said if true would be a (unexpected) problem.

I do have the proper equipment at work (gas chromatograph/mass spectrometer) that I can quantify ethanol in fuel. I would need to get several samples (e.g. different brands grades) of corn fed for comparison and find the time to run the samples. Might take a few weeks to put together but will post the results here if I do.

 

[Lakeside53]

I've been running an echo CS-300, Stilh 290, 066, and 660 on the same jobs with the same gas can and crew. All of my equipment stays under lock and key when I'm not around unless the foreman is running the crew so malicious intent is not one of the causes that I am considering.

Could use and vibration lead to the carb adjustments moving slightly?

Here are the pics.

I hate to break it to you but that 066 saw was run on straight gas... Someone is not telling you the entire story... And what's more.. who ever was using it is NOT listening to the saw.... or didn't care.


The 660 failure is different. Could have been a bad carb adjustment or fuel.

 

[kevlar]

I hate to break it to you but that 066 saw was run on straight gas... Someone is not telling your the entire story... And what's more.. who ever was using it is NOT listening to the saw....


The 660 failure is different. Could have been a bad carb adjustment or fuel.

I agree the 066 was smoked! The 660 (poor picture) looks almost like carbon scoring.

 

[OilHead]

What are these saws taching out at? Probably set 'em around 12.5k rpm for the knuckle-dragging crowd, 13.5k for the folks who know what they're doing.

What are you using for fuel and premix oil? Who mixes the gas?

Clearly someone is doing something wrong.

My 066 Book shows max rpm at 13 k. When I purchase my fuel I pump 1 gallon of the best premimum into the vehicle then despence .9 of a gallon into the container so to be sure there isnt some residule low grade left over in the delivery hose & filter at the pump. To that add the bottle . If your using the 2 1/2 gal. bottle despence 2.25 gallon. That should put the mixture around 45-1. Just a little added insurance for just this kind of thing. We have ethanol in the fuel here & it tends to make things run hotter .

 

[yungman]

What are these saws taching out at? Probably set 'em around 12.5k rpm for the knuckle-dragging crowd, 13.5k for the folks who know what they're doing.

What are you using for fuel and premix oil? Who mixes the gas?

Clearly someone is doing something wrong.

Not to change the subject, I like your poster of Hilary!!! you mean your don't like to be in People's Republic of the good old U S of A!!!!!!!:hmm3grin2orange: :hmm3grin2orange: :hmm3grin2orange:

While I am here, might as well ask: You guys mensioned about reading the plug to judge whether the air fuel is out of weck. Does this mean if I see the plug after running full throtle for a little while, shut off while it is wide open, check the plug. If it is medium or dark brown, I am in the ball park, I don't have to worry about the carburetor for a while? If it is light color or white, I need to do something right away?

 

[huskydave]

Those rings are stuck. Don't run that saw. The cylinder might be savable. The piston is finished. Do you clean your exhausts out once and a while? I think carbon gets into the cyl from dirty mufflers and scores pistons. I would try and find out whats going on starting with the carb and set it up a little rich if your running the saws hard. I clean out the mufflers/exhaust ports every 2-3 weeks it prevents scoring in my opinion. Oh and Im with Lake on something is fishy What do the chains look like? I bet they are dull.

 

[bcorradi]

Eventhough its less likely...there really isn't anyway to distinguish that the saw was run on straight gas vs the highspeed jet turned all the way in.

I guess if the tank currently has mixed gas in it you know for sure that it wasn't an accident or if it was an accident they tried to cover it up.

 

[Lakeside53]

While I am here, might as well ask: You guys mensioned about reading the plug to judge whether the air fuel is out of weck. Does this mean if I see the plug after running full throtle for a little while, shut off while it is wide open, check the plug. If it is medium or dark brown, I am in the ball park, I don't have to worry about the carburetor for a while? If it is light color or white, I need to do something right away?

No... Many later moel lean running OPE will show a light or whiteish plug and be fine - MS361 for instance..

Plug reading is "interesting" but not definitive.

 

[Tree Student]

I agree the 066 was smoked! The 660 (poor picture) looks almost like carbon scoring.

If you will notice in the 660 piston pic the top edge of the piston broke off and scored the side of the piston but did not harm the cylinder wall or exhaust port.

I am the only one who sharpens the chains and my foreman is the one that runs saws other than me so he gets his ass reamed for running a dull chain and he has a habit of changing chains before they get to the dull point because we are using such aggressive chains.

I pulled up on site as the saw started acting up so I saw the fuel that was left in the tank and it was a mix, the same mix was then ran for the rest of the day in the 290.

The 066 is now at the saw shop and with all the information that I was able to give it is suspected to have a bad electronic ignition module but he is tearing into it after pressure testing it and I'll get those results this evening.

Thanks for all of the input guys, I'm learning more than I expected already and that was my goal. I suspect that we are not watching the gas mix enough and the atmosphere down here has been rather dry the past few days so maybe a combination of that and running it so hard cutting firewood caused my latest problem.

 

[Andyshine77]

I would suggest mixing your fuel at 40:1 or 32:1 if your crew is running your saws as hard as you say they do. You also need to buy a tachometer and check your rpm's every day, or when the weather changes.

That 066 was run on straight gas, or it had a big time air leak...