Too lean/air leak most likely caused it. The piston seems loose because the lack of lube wore the piston down. There's no compression because the rings are most likely stuck, have alm. transfer on them, or simply wore for lack of lube.
Uneven Piston Wear on MS 660
- Thread starter Wood Doctor
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watsonr
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Higher than normal levels of Ethanol in any level of octane are saw killers, not just low octane rated fuel. Every drop of that crap attracts water and could cause a lean seize just like this one. Could have been the fuel, high level of ethanol, no oil, water or an air leak. My fuel is rated at 10% ethanol in EVERY product... 87, 89, 91, and 93 and is no lower in one or the other. Running a minimum of 89 is recommended. I've run 87 octane non-E fuel without any issues for years!
You gave the answer in the comments above.... Ethanol will do terrible things... more so than octane rating, octane did not kill this saw.
Fabulous Article
Madsens looks like they have it all together. I purposely did not touch the carb settings when I took down the saw and did not look at them until now. These carb screws have the "idiot-proof" plastic blocks on them. However, the high speed setting was under 1/4 turn open. In my book, this engine must have been running too lean. I have no idea who set it at that level, but I recall setting the high a full turn open before I returned the saw to Andy last spring. He usually adjusts nothing, but somehow this saw was running lean.
I suppose there are other possibilities, including too much water vapor due to a sudden change in weather conditions. This saw is always stored in an unheated garage or in the bed of a pickup truck. However, I doubt that was the cause. I also doubt that any major air leak existed because the engine idled correctly until the day it died. Air leaks usually prevent the saw from dropping down to normal idle speed. The engine will siimply shut down below 5000 RPM.
Summary: Based on the high speed setting at only 1/4 turn open, I think the lean fuel mixture ruined the piston, the rings, and the cylinder, with practically all the damage on the exhaust port side. The cylinder is beyond repair, literally reamed out. I have another one in the shop to compare it with. The engine could likely have been running this way for a dozen hours or more and eventually there was insufficient compression for combustion.
Thanks men, and especially Madsens for a terrific article and Wheelman for the URL to the site.
Madsens looks like they have it all together. I purposely did not touch the carb settings when I took down the saw and did not look at them until now. These carb screws have the "idiot-proof" plastic blocks on them. However, the high speed setting was under 1/4 turn open. In my book, this engine must have been running too lean. I have no idea who set it at that level, but I recall setting the high a full turn open before I returned the saw to Andy last spring. He usually adjusts nothing, but somehow this saw was running lean.
I suppose there are other possibilities, including too much water vapor due to a sudden change in weather conditions. This saw is always stored in an unheated garage or in the bed of a pickup truck. However, I doubt that was the cause. I also doubt that any major air leak existed because the engine idled correctly until the day it died. Air leaks usually prevent the saw from dropping down to normal idle speed. The engine will siimply shut down below 5000 RPM.
Summary: Based on the high speed setting at only 1/4 turn open, I think the lean fuel mixture ruined the piston, the rings, and the cylinder, with practically all the damage on the exhaust port side. The cylinder is beyond repair, literally reamed out. I have another one in the shop to compare it with. The engine could likely have been running this way for a dozen hours or more and eventually there was insufficient compression for combustion.
Thanks men, and especially Madsens for a terrific article and Wheelman for the URL to the site.
