Understanding JASO T 903 and JASO T 904 Engine Oil Standards

Passenger vehicles often integrate friction modifiers to enhance fuel efficiency, a feature not suitable for wet clutch systems. Unlike cars, motorcycles typically employ the same oil for both engine and clutch, necessitating precise frictional properties to prevent clutch slippage. The JASO classifications, namely JASO T 903 and JASO T 904, address this need.

What is JASO T 903?

JASO T 903, established by the Japan Automobile Standards Organization (JASO) in 1998, serves as the benchmark for motorcycle 4-stroke engine oil. While standards like API, ILSAC, and ACEA cater mainly to the automotive sector, prioritizing lower viscosity and friction for better fuel economy, they may not suit motorcycles. The use of low-viscosity, low-friction oil in motorcycles can lead to clutch slippage and transmission damage due to lubricating multiple components with the same oil. To address this, JASO T 903 was introduced as a motorcycle-specific standard.

According to JASO T 903, the oil must meet specific requirements:

• Minimum Friction Characteristic: Crucial to prevent clutch slippage.
• Maximum Viscosity Degradation: Ensures oil maintains its viscosity under severe shear forces between transmission gears.

JASO T 904

JASO T 904 evaluates the friction property of a wet clutch in motorcycle systems. It comprises two standards: MB and MA. MB, the basic standard, is suitable for low-power scooters but may cause clutch slippage. MA offers improved performance, with subclasses MA1 and MA2 introduced in 2006 to refine the classification further.

• MA1: Provides minimal slippage, suitable for various applications.
• MA2: Offers enhanced frictional performance and clutch engagement, allowing manufacturers to tailor formulations for specific requirements.