Four Stroke Cycle Gasoline Engine Oils for Motorcycle 2006-32-0015
Conventionally, the engine oils for passenger cars have been used as four stroke cycle gasoline engine oils for motorcycle from old-time. However, the engine oils for passenger cars have been required to have fuel economy performance, and these engine oils are not fit in the requirement of motorcycles because of low friction and low viscosity. For this reason the four stroke cycle gasoline engine oils for motorcycles have been classified into two categories of ‘MA’ and ‘MB’ based on differences in friction characteristics according to standard of Japan Automobile Standards Organization (hereinafter referred to as ‘JASO’) -JASO T 903:1998. In currently, some engine oils for passenger cars can fit in JASO standard, but the range of friction coefficient in MA category is becoming wider. When such a low-viscosity, low-friction coefficient engine oil is used in four stroke cycle engines for motorcycles in which the same engine oil is commonly used for lubricating of the engine, the clutch and the transmission, the clutch slipping may occur because of the low friction coefficient or the gear durability may be deteriorated because of the low viscosity property in some types of motorcycles. Also, sometimes clutch slipping which appears to be caused by the above reasons have been reported from motorcycle users to motorcycle manufacturers and clutch manufacturers. The revision of JASO T 903 standard was decided to revise for improving of the subjects on the opportunity of periodic revision in 2006. The working group named ‘Motorcycle Four-cycle Engine Oil Standards Revising Working Group’ was organized with motorcycle manufacturers, clutch manufacturers, oil manufacturers and additive manufacturers in Society of Automotive Engineers in Japan, and the contents of the revision were discussed. As a result, the necessity of high friction coefficient in the MA category for wet clutch which require high friction coefficient, became understood, and MA category of JASO T 903 standard was decided to being divided into two categories. In the MA category, the engine oils with a high friction coefficient was defined as ‘MA2’, and the engine oils with a low friction coefficient was defined as ‘MA1’, respectively. Also, the regulation for the viscosity and the stipulation for the amount of phosphorus were revised from the viewpoint of gear durability and fuel economy improvement. This report herein introduces the result of the discussion process and the characteristics of motorcycle engine oil.