Development of Lubricants for High-Performance Two-Stroke Cycle Engines

This paper presents a review of the lubricant development for the air and water-cooled two-stroke cycle engines manufactured by the McCulloch Corp. The differences in engine designs, field operating conditions, and test procedures are discussed.

Major emphasis is placed on lubricant development for mixture ratios greater than 20:1 in order to improve starting, idling, and spark plug life and to reduce exhaust smoke. It was found that these leaner mixture ratios necessitated higher detergent levels to maintain the same engine cleanliness. Eliminating the bright stock from the oils decreased the carbonaceous deposits, but increased susceptibility to piston seizure in the aircooled engines. Addition of a high molecular weight polymeric thickener decreased this seizure tendency without causing additional deposits.