JASO (Japanese Automotive Standards Organization) is an organization consisting of major vehicle manufacturers in Japan. It was created as the Japanese equivalent to the API (American Petroleum Institute) specifications because those were not suitable for the unique specification needs of modern Japanese engines. The API specifications are constructed for automobile engines but not for motorcycle engines.
Car oils have been used up to 1998 as the base for most motorcycle oils. But as the technology in cars evolved, the oils were modified to meet those modern needs. As a result, additives were added and friction modifiers were blended with the oil. Although these modifications were positive for use in cars, they were damaging to motorcycles. This was especially the case with motorcycle gearboxes and clutches. Unlike with cars, motorcycles don’t use a separate oil for the gearbox, causing the clutches to slip due to the friction modifiers. It also could attribute to gearbox pitting (localised corrosion and the formation of micro-cracks). Oil in motorcycles and scooters is required to run under more intense conditions than in cars because it has to endure hotter temperatures as well as higher engine speed and a greater power density. These circumstances subject the oil to significant operating stress.
In 1998 JASO T903 was introduced as the globally recognized standard for 4-stroke motorcycle oils. It defines the required performance levels for satisfactory lubrication of the different motorcycle designs.
JASO T903 consists of two performance categories:
- JASO MA: Oils for motorcycles with a wet clutch. These oils deliver the needed friction performance to prevent the clutch from slipping and are therefore non-friction modified. These oils can be used in 4-stroke motorcycle engines where there is one oil system in place for the engine, gearbox and clutch. MA oils are suitable for all applications.
- JASO MB: Oils for motorcycles with an automatic transmission (scooters). These oils deliver the needed friction performance by added friction modifiers which provide fuel economy benefits. These type of oils are ranged as the lowest friction oils in 4-stroke motorcycle oils. MB oils should not be used when a MA oil is required as they could induce clutch slippage in motorcycles and should therefore only be used in scooters. The transmission in scooters is done by use of belts or chains and does therefore not require any oil.
An oil is either MA or MB based on the outcome of the JASO T903 Clutch Friction test. In this test the performance of three friction performance areas is evaluated, making sure the oil is suitable for wet clutch applications.
- Dynamic friction: The feel of the clutch and the power transfer during clutch engagement.
- Static friction: The capacity of the torque handling and the resistance against slipping during breakaway conditions.
- Stop time: How quickly the clutch is engaging.
The main difference between JASO MA and MB is whether the oil is suitable for a wet clutch or not.
In 2006, MA1 and MA2 were added as extra categories within the JASO MA specification. The main difference between these two categories is the higher friction performance MA2 oils are delivering. This meant that from 2006 on, motor oils that meet the T903:2006 standard can be divided into four specifications for 4-stroke motorcycle oils:
- JASO MA: This is the standard specification for oils that are used within one oil system (where the engine, gearbox and clutch use the same oil). These oils don’t contain any friction modifiers.
- JASO MA1: This is a lower standard specification for motorcycles that require different oils for the engine, gearbox and clutch.
- JASO MA2: This is a higher standard specification for modern motorcycles. These oils are suitable for use in motorcycles that have catalytic converters in the exhaust system.
- JASO MB: This is a lower standard specification for scooter engines.
For an oil to meet any of the above mentioned JASO specifications, it has to meet at least one of the following quality levels:
- API SG, SH, SJ, SL, SM
- ILSAC GF-1, GF-2, GF-3
- ACEA A1/B1, A3/B3, A3/B4, A5/B5, C2, C3
Although the above motorcycle oil specifications are by far the most important and worldwide recognised, JASO already introduced a rating system for 2-stroke oils in 1994. The tolerances of modern 2-stroke motorcycles and scooters are much smaller and also require an oil that generates less ash.
The JASO 2-stroke oil classifications are:
- JASO FA: This is the lowest specification that tests lubrication capability, detergency, initial torque, exhaust smoke and exhaust system blocking. This specification has been officially declared obsolete in 2005 although it is still being used.
- JASO FB: This specification is slightly higher than JASO FA and tests the same characteristics. It requires increased lubrication capability, detergency, exhaust smoke and exhaust system blocking. It corresponds with ISO Global Specification EGB.
- JASO FC: This specification requires the same results for the tests of lubrication capability and initial torque as JASO FB but has higher standards for detergency and exhaust smoke and exhaust system blocking. It corresponds with ISO Global Specification EGC.
- JASO FD: This specification has the same standards as JASO FC except for a higher detergency requirement. It corresponds with ISO Global Specification EGD.
Always check the owner’s manual to see which specification is required. If both an API and JASO MA specification are listed, make sure you pick an oil that qualifies for both specifications.
Apart from the above described worldwide recognised specifications JASO also defined the following (partly with API or ACEA correlating) oil specifications.
- JASO DL-1: An oil specially designed for Light Duty Diesel Engines equipped with exhaust after treatment devices.
- JASO DH-1: A high sulphated ash oil designed for the lubrication of Heavy Duty Diesel Engines, not suitable for exhaust after treatment devices.
- JASO DH-2: A low sulphated ash oil designed for the lubrication of Heavy Duty Diesel Engines, particularly when equipped with exhaust after treatment devices.
- JASO GLV-1: An ultra-low viscosity, fuel saving, passenger car engine oil.
- JASO 315-1A: A specification defining a Dexron Vi automatic transmission fluid type. This specification is now renamed to JASO 1-A.