Officials noted that that dependency on passenger car engine oils has affected the products available for use in two-wheeled vehicles.

“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.”

Furthermore, the continuing charge toward lower emissions has led to significant changes to motorcycle engine technology over the years. “As motorcycle markets around the world continue to legislate for tighter and tougher emissions standards, the move from carburetor to port fuel injection technology has been widely adopted by OEMs as an enabling technology for lower emission hardware,” according to an article published by major additive supplier Lubrizol earlier this year. “This change has also enabled increased engine power densities, resulting in more severe engine oil operating conditions. As a consequence, there is a need for increasingly robust piston cleanliness performance as well as improved oxidative and thermal stability.” 

What’s New?

The engineering society improved the level of wear protection by updating the list of incorporated passenger car engine oil specifications, which have raised antiwear performance over the years as viscosity thinned for those products, too. This year’s update removes the two oldest API specifications included in the 2016 iteration of the motorcycle oil specification—API SG and API SH—and two specifications that have hit the 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 a reporter for Lubes’n’Greases’ Lube Report in early July. Miura served as chairman of the Society of Automotive Engineers of Japan’s Engine Oil Subcommittee and led the charge for the development of the current 2016 JASO standard.

API SN Plus was developed to address the problem of low-speed pre-ignition, which was a phenomenon that had developed in some passenger cars that 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.”

Figure 1. Specifications and Quality Categories

Other notable revisions to the Japanese motorcycle oil specification include the following:

• The revised specification will remove references to ILSAC and ACEA passenger car engine oil standards. Until recently, they could be used instead of API specifications to measure performance for core requirements, but applicants for T903 licenses were using just the API standards. 
• The updated JASO specification will lower the maximum limit for phosphorus content from 12% to 10.2%. Reducing phosphorus content improves protection of exhaust catalysts in emissions control systems designed to help vehicles meet increasingly stringent emission standards. The updated specification maintains the lower limit for phosphorus content at 8% in an effort to ensure adequate protection against wear. Phosphorus derivatives are popular antiwear agents.
• The JASO T 903:2023 standard will change the reference oils from JAFRE-B16 to JAFRE-B23 to ensure ready availability.
• Finally, the revised specification will replace the friction plate used in evaluation tests to mitigate concerns about supply availability.

Formulation Challenges

The new requirements set out by the new JASO specification will ensure better protection of modern hardware. However, the more robust standard comes with some formulation challenges. According to Lubrizol, additive selection and concentration are a bit tricky under JASO T 903:2023. 

Figure 2. New Limits

“The trend toward use of lighter viscosity oils for increased fuel efficiency reduces oil film strength and places increased stress on the additive antiwear system,” the company explained on its website. “This has the potential to give rise to wear durability issues; however, formulating to counter this is made more challenging by increased restrictions in phosphorus content. The need to deliver enhanced catalyst compatibility effectively limits the use of conventional antiwear chemistry. This requires the use of novel antiwear components and a different formulating approach to ensure a balanced approach to deliver the performance, efficiency, durability and catalyst compatibility required by the latest hardware.”

Let the Licensing Begin

Any formulations registered under the T903:2011 version of the motorcycle oil specification expired in April 2021, according to the JASO Engine Oil Standards Implementation Panel. 

Acceptance of new applications for 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 latest JASO T903:2023 standard will begin from October 1, 2023.  

Lam Lye Ching and George Gill contributed to this article.

Sydney Moore is managing editor of Lubes’n’Greases magazine. Contact her at Sydney@LubesnGreases.com