The Japanese Society of Automotive Engineers has updated its JASO T 903 performance specification for four-stroke motorcycle engine oils, incorporating the latest API passenger car motor oil standards in an effort to protect gears and other equipment as the market trends toward lower-viscosity and lower friction products.
The update was published on the Japan Lubricating Oil Society website in May, after adoption by JSAE, and licensing of products meeting it is scheduled to begin in October. The world’s most-used motorcycle oil spec was last updated in 2016.
As with previous versions, the updated spec, officially known as the JASO T 903:2023 or “Motorcycles Four-Stroke Cycle Gasoline Engine Oils,” incorporates requirements of PCMO standards but adds additional parameters, such as a test that measures an oil’s ability to provide the friction performance needed for the motorcycle’s clutch system.
Officials noted that that dependency on passenger car oils has affected the products available for two-wheelers.
“In recent years, engine oils for four-wheel vehicles have tended toward lower viscosity and lower friction to achieve better fuel economy,” according to the JASO T 903:2023 Implementation Manual. “There are concerns that such low friction and low viscosity oils, when used in motorcycles, may cause clutch slippage and transmission gear pitting wear. Field problems have actually been observed that are probably attributable to such problems. Because of this, there was a strong demand by Japanese motorcycle manufacturers to develop new four-cycle oil standards.”
The engineering society improved the level of wear protection by updating the list of incorporated passenger car oil specs, which have raised antiwear performance over the years as viscosity thinned for those products, too. This year’s update removes the two oldest API specs included in the 2016 version – API SG and API SH – and two specs that came to market since 2016, API SN Plus and API SP. The new update also retains API SJ, API SL, API SM and API SN.
“For motorcycles, oil performance above SJ is sufficient,” Miura Tohru, supervisor of Yamaha Motor Co Ltd.’s Platform Vehicle Unit Quality Innovation Engineering Department, Powertrain quality group, told Lube Report. Miura served as chairman of the Society of Automotive Engineers of Japan’s Engine Oil Subcommittee and led the development of the current 2016 JASO standard.
API SN Plus was developed to address the problem of low-speed pre-ignition, which had developed in some passenger cars and was causing sometimes catastrophic engine wear. For the time being, Miura said, “there is no problem with low-speed pre-ignition in motorcycles, and the inclusion of SN Plus is to expand the range of choices. However, there may be a need in the future and in that case, SJ, SL and SN will be removed.”
Other changes include:
● removing references to ILSAC and ACEA passenger car engine oil standards. Until now they could be used instead of API specs to measure performance for core requirements, but applicants for T903 licenses were only using the API specs.
● lowering the maximum limit for phosphorus content from 12% to 10.2%. Reducing phosphorus content improves protection of exhaust catalysts in emissions control systems built to help meet tougher emission standards. The updated spec maintains the lower limit for phosphorus content at 8% in an effort to ensure adequate protection against wear. Phosphorus derivatives are popular antiwear agents.
● changing the reference oils from JAFRE-B16 to JAFRE-B23 to ensure availability.
● replacing the friction plate used in evaluation tests due to concerns about supply availability.
Acceptance of new applications of the JASO T 903:2016 standard will end on September 30 this year, and the current T903:2016 on file data will expire on April 30, 2028. Licensing of the new JASO T903:2023 standard will begin from October 1, 2023.