In 1947, the Society of Automotive Engineers established a standard for motor oils used in four-cycle engines. The standard was updated and changed in 1970 to reflect improvements in oil quality mandated by engine manufacturers. This current rating system for motor oils has assisted consumers in selecting the proper oil for use in their four-cycle engines.
Until recently, there had been no rating system for oils used in two-cycle, air-cooled engines. In fact, many owners of two-cycle engines were using motor oil designed for four-cycle engines. Motor oil will mix well with gasoline and appears to function as well as two-cycle oils. In this case, appearances are deceiving.
"SP268-I-Oils for 2-Cycle Engines," The University of Tennessee Agricultural Extension Service, SP268I-2M-11/98(Rev) E12-2015-00-049-99, http://trace.tennessee.edu/utk_agexmach/1