Marvinlee
ArboristSite Member
I had promised to provide tech reference on one ring pistons. Two of them are SAE reports. The oldest is SAE report # 840183 titled "Some Studies on Two Ring Pistons in Automobile Turbocharged Engines," by Shoichi Furuhama, a noted Japanese scholar in piston and ring research. The second is SAE paper #910435 titled ", by Furuhama and several other researchers. I have read a very recent report in a tribology (study of friction and wear) journal but did not locate it on my most recent library visit.
Several engines have used single compression rings, including the first series Caterpillar 3208 engine, the 2008 Honda 150R motocross motorcycle, the Kawasaki KX 250F, and the 2001 Honda Civic 1.5 liter lean burn engine. These engines span a range from large to small.
Note that the engines listed above are four cycle. A two-ring four cycle piston has, actually, only one compression ring, the same number now being used in some two-cycle engines. From the viewpoint of compression rings, a two-ring four cycle engine is the same as a one-ring two cycle engine.
Concern has been expressed over potentially short piston ring life in one-compression-ring pistons. A shorter ring life is conceivable. It is up to the scrupulous engine designer to ensure that a potential outcome does not become reality. Counter measures for the engine designer to consider include but are not limited to, gas nitriding, steel rings, nodular iron instead of plain cast iron material, chrome or chrome-ceramic ring coatings, more careful distribution of piston ring radial thrust forces, twisted rings (yes, truly), increased cooling fin area to compensate for the reduction of ring area for heat to pass through, improved cylinder liner coating, and closer tolerance control. The latter is more important when only one ring exists to control blow by.
My personal experience with a one-ring 5100S Dolmar has been positive to date, but it is too soon to judge ultimate engine life. In any case, engine life varies widely from one individual to the next, even of the identical design. It is only over a larger population of engines that one can form sound conclusions concerning the effects of a design change.
Considering everything, I believe that a name brand engine using a single ring should not be avoided on that account. Recall that small two-stroke engines are intended to last a relatively short time, perhaps a thousand hours or less, while industrial engines may last more than ten times as long. The EPA requires only 300 hour or less expected life for the engines' emission control, and the EPA tends to link required emission control durability to expected engine durability.
I am not an expert on ring design, and regret if my comments have created that impression. I welcome other views, contradictory to my own or not.
Several engines have used single compression rings, including the first series Caterpillar 3208 engine, the 2008 Honda 150R motocross motorcycle, the Kawasaki KX 250F, and the 2001 Honda Civic 1.5 liter lean burn engine. These engines span a range from large to small.
Note that the engines listed above are four cycle. A two-ring four cycle piston has, actually, only one compression ring, the same number now being used in some two-cycle engines. From the viewpoint of compression rings, a two-ring four cycle engine is the same as a one-ring two cycle engine.
Concern has been expressed over potentially short piston ring life in one-compression-ring pistons. A shorter ring life is conceivable. It is up to the scrupulous engine designer to ensure that a potential outcome does not become reality. Counter measures for the engine designer to consider include but are not limited to, gas nitriding, steel rings, nodular iron instead of plain cast iron material, chrome or chrome-ceramic ring coatings, more careful distribution of piston ring radial thrust forces, twisted rings (yes, truly), increased cooling fin area to compensate for the reduction of ring area for heat to pass through, improved cylinder liner coating, and closer tolerance control. The latter is more important when only one ring exists to control blow by.
My personal experience with a one-ring 5100S Dolmar has been positive to date, but it is too soon to judge ultimate engine life. In any case, engine life varies widely from one individual to the next, even of the identical design. It is only over a larger population of engines that one can form sound conclusions concerning the effects of a design change.
Considering everything, I believe that a name brand engine using a single ring should not be avoided on that account. Recall that small two-stroke engines are intended to last a relatively short time, perhaps a thousand hours or less, while industrial engines may last more than ten times as long. The EPA requires only 300 hour or less expected life for the engines' emission control, and the EPA tends to link required emission control durability to expected engine durability.
I am not an expert on ring design, and regret if my comments have created that impression. I welcome other views, contradictory to my own or not.
