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I am thinking about this issue with cylinder walls lubrication and perhaps why 2T oil works for 4 stroke engines. We all know that most cars have 3 sets of piston rings. 2 for compression and 1 for oil. http://www.federalmogul.com/korihandbook/en/section_8.htm For more info about piston rings, check out the link above. I am thinking that when the piston moves down, the oil scrapper ring will remove most of the oil on the cylinder walls. This means there is very little oil left on the walls. When the piston moves up again, wouldn't there be metal-metal contact since the cylinder walls have hardly any oil? Pistons rings uses high wear resistance materials or coatings/plating (as shown in the link) proves that they do wear out and there is contact and lots of friction. IMHO, why 2T oil works is because when air/fuel mixture enters the combustion chamber, some of the fuel will cling onto the cylinder walls, hence creating a thin layer of lubrication. Hence reducing friction as the piston moves up. What do you guys think?

http://theoildrop.server101.com/forums/sho...ge=0#Post724753 Read and learn why 30wt or 20wt is good enough.