Damaging Pistons and Cylinders on 660s

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Tree Student

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Has anyone had a problem with 066's or 660's that score the piston and cylinder?

I've had two in the past month while cutting firewood, fuel mixture is correct and used in other saws with no issue but most damage seems to be on the exhaust port side. Will add pictures this evening.

Any input or suggestions are appreciated.
 
Tree Student said:
Has anyone had a problem with 066's or 660's that score the piston and cylinder?

I've had two in the past month while cutting firewood, fuel mixture is correct and used in other saws with no issue but most damage seems to be on the exhaust port side. Will add pictures this evening.

Any input or suggestions are appreciated.
Click to expand...
I believe your 066/660 is running too lean. If the fuel mix is correct like you say, I would double check your other saws to make sure they aren't running too lean or else its going to get more expensive in a hurry.

If the 066/660 is running erratically it could possibly be other issues like an air leak specific to that saw.
 
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bcorradi said:
I believe your 066/660 is running too lean. If the fuel mix is correct like you say, I would double check your other saws to make sure they aren't running too lean or else its going to get more expensive in a hurry.

If the 066/660 is running erratically it could possibly be other issues like an air leak specific to that saw.
Click to expand...

Each time the saw is running fine then it won't idle and it's hard to start.

Guess tomorrow is going to be inspection day instead of cutting firewood.
 
Mad Professor said:
If mix is correct ,check plug(s) to see if carb mixture setting is O.K.

Are you running fresh mix? Also crap gas with ethanol degrades mix much faster.
Click to expand...

Fresh mix every few days at a minimum, it's not an exact mix but very close.

Please explain what I am looking for on the plug to see if the carb mix setting is OK.
 
The 066/660 doesn't have a problem. If you have multiple saws doing the same thing, it's either fuel, mix oil, or the H setting on your carbs. This assumes you change your fuel filter at least once a year.. and don't use metal cans with rust in the bottom..

Unless you have experience, ignore the plug. If you have a limiter cap carb the H adjuster should be fully Counter-clockwise.
 
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Lakeside53 said:
The 066/660 doesn't have a problem. If you have multiple saws doing the same thing, it's either fuel, mix oil, or the H setting on your carbs. This assumes you change your fuel filter at least once a year.. and don't use metal cans with rust in the bottom..
Click to expand...

Plastic can only for fuel, can't stand the rust. Did major servicing such as changing all filters and spark plugs in Oct.

The 64/66/660's are my only saws to have this issue so far, 066 and 660 happened recently and the 064 had worn out jets in the old carb.

I have experience in running saws for years but we always had the local saw shop do all the maintenance and repairs, trying to learn more about doing my own servicing now. 4 cycle engines I can do but haven't had enough experience with working on 2 cycle engines yet.
 
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Ok the hard starting could be due to a lack of compression because of the scoring. The erratic idle could also be due to this, but its really hard to diagnose it without more information. Your best bet would be to get the saw pressure tested. There are a few guys on here from texas that I believe have affiliation with stihl dealers so maybe they could help you out.
 
Are we talking multiple saws or the same saw?

If it's happened TWICE on the SAME saw, then you need to look really carefully at the carb, etc..

Are you sure you guys aren't "tweaking" the carb??
 
Lakeside53 said:
Are we talking multiple saws or the same saw?

If it's happened TWICE on the SAME saw, then you need to look really carefully at the carb, etc..

Are you sure you guys aren't "tweaking" the carb??
Click to expand...

Two different saws, one 660 before and a 066 today, my crew doesn't have anything small enough to adjust the carb and I check on them often and work with them when I am not bidding jobs or running errands.
 
On a saw before it is to late

To read a plug. It can not be a brand spanking new plug it has to have some deposits on it to read effectively. Warm up the saw for a few minutes by cutting.Then go full throttle into wood cut a good ways through then hit the kill switch while it is wide open throttle. Then remove the plug.Look at the plug in the daylight. It should be a carhart brown in color., In your case dark brown to black would be better.. Seeing how you have other people running the life out of your saws. If the plug is white you are way to lean. Back the H needle out. and try it again.If the plug is aluminum in color,(basically coated you are a day late)
 
ericjeeper said:
To read a plug. It can not be a brand spanking new plug it has to have some deposits on it to read effectively. Warm up the saw for a few minutes by cutting.Then go full throttle into wood cut a good ways through then hit the kill switch while it is wide open throttle. Then remove the plug.Look at the plug in the daylight. It should be a carhart brown in color., In your case dark brown to black would be better.. Seeing how you have other people running the life out of your saws. If the plug is white you are way to lean. Back the H needle out. and try it again.If the plug is aluminum in color,(basically coated you are a day late)
Click to expand...

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.
 
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.
 

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