JASO Explained Part 1: 4-Stroke

JASO Explained1

JASO Explained PART 1:

JASO 4-Stroke Engine Oil Specification

       The Japanese Lubricating Oil Society or JALOS is the organization that regulates the performance of various motorcycle specific engine oils. JALOS is the organization that regulates and oversees the implementation of the JASO motorcycle engine oil specifications. For motorbike applications, there are two separate JASO categories for 4-stroke and 2-stroke applications with numerous subdivisions within each category. I am going to split this article into two parts to focus on each main category separately.

       Let’s begin with a quick background of the 4-stroke JASO specification. In 1998, JALOS organized the first widely accepted standard for evaluating performance of motorcycle engine lubricants. This was necessary due to an increasing number of automotive oils meeting the energy conserving and resource conserving specifications through the technology of friction modifiers. Because these friction modifiers are not designed for compatibility of wet clutches, problems were occurring in motorcycles utilizing a common oil sump for both the engine and transmission. The MA specification was launched in 1998 with the attempt to differentiate between products that were suitable for wet clutch applications and those that weren’t. This was done in collaboration with the major motorcycle manufacturers of Japan at the time so it was a fairly industry-wide desire to identify the products that worked most effectively. The first two categories introduce by JALOS were the JASO MA and the JASO MB performance specifications. The MA category was originally meant for good clutch compatibility and MB was for products not compatible with wet clutches, or in other words; products that contain friction modifiers and cause clutch slip.

       In 2006 the T903:1998 specification was replaced by the T903:2006 specification which underwent a big change to the clutch friction test results and their interpretation. The specification for JASO performance in wet clutch applications was further broken down into three oddly distinct yet overlapping categories. In 2011 the T903:2006 specification was replaced by the T903:2011 specification in order to further refine those friction result ranges for each category. The charts below lay out the exact ranges for each category during each update and make it simple to see how they are currently broken down.

JASO T903 1998 chart
Figure 1: JASO T903:1998 Clutch Friction Specification
JASO T903 2006 chart
Figure 2: JASO T903:2006 Clutch Friction Specification
JASO T903 2011 chart
Figure 3: JASO T903:2011 Clutch Friction Specification
Figure 4: JASO T903:2016 Clutch Friction Specification
  • MB – To be classified as MB, at least one of the three results needs to be within the MB ranges. It can be any one of the three, it could be two of three or it could be all three, but at long as at least one result is within the MB range, the entire oil performance is considered MB.
  • MA1 – To be classified as an MA1 oil, all three of the results must be within the MA1 range.
  • MA2 – To be classified as an MA2 oil, all three of the results must be within the MA2 range.
  • MA –  To be considered MA, all three results must be within the MA range. Since the MA range encompasses both the MA1 and the MA2 specifications, it can become a little confusing. Technically, if a particular oil meets the MA1 specification, a lubricant marketer can call it an MA oil and the same applies to an oil that meets the MA2 specification. If an oil’s results are mixed and some of the results are within the MA1 range and some are within the MA2 range, then it can only be classified as MA.

       So that is how the clutch compatibility is currently tested. The SAE #2 bench test is the most current testing protocol to determine performance at the time I am writing this article. To put it simply, MA covers the entire clutch compatible range, MA1 is the lower friction half of that specification and MA2 is the higher friction half of that specification. These friction test results are the only differences between the four JASO categories for 4-stroke motorcycle engine oil.

       The result names of DFI, SFI and STI are kind of nondescript and difficult to assign a practical property to. It took me quite a long time before I found a detailed enough description of each one to fully understand each result. Here is a basic description of what each one means:

  • Dynamic Friction Index (DFI) – Is a measurement of how power is transferred while being operated under slipping conditions or in other words, how the clutch feels as it is engaged when already spinning.
  • Static Friction Index (STI) – A measure of how much torque can be applied to an already fully engaged clutch before slipping occurs.
  • Stop Time Index (STI) – A measurement of how much time it takes for the clutch to engage when the lever is released.

    There is another series of tests that are required for JASO compliance that relate to performance characteristics other than wet clutch compatibility. Here is the exact specification followed by a brief description of each item. (Many of the tests are already listed in MotoTribology’s glossary.)

Figure 4: JASO T903:2011 laboratory bench testing requirements. Thesespecifications control the chemical and physical properties of motorcycle specific oils.
Figure 5: JASO T903:2011 laboratory bench testing requirements. These specifications control the chemical and physical properties of motorcycle specific oils.
  • Density – A measurement of mass per given volume
  • Flash Point – A way to measure the flammability characteristics of a fluid. It is measured by determining the temperature at which the oil vaporizes rapidly enough to make the volume of air directly above the liquid flammable.
  • Kinematic Viscosity – A measurement indicating a fluids ability to flow. The more viscous oil is, the thicker it is. This is sometimes referred to as low shear viscosity. While the result at 40°C only needs to be reported, the result at 100°C must correlate to the designated SAE viscosity grade on file for the product.
  • Viscosity Index – A number which is calculated using the kinematic viscosity of a fluid at varying temperatures. Simply put, it is a measure of how stable the viscosity is over a wide temperature range. The higher the viscosity index number is, the more stable a fluid is with regards to viscosity.
  • Low-Temp Viscosity, CCS – The low temperature viscosity of an oil in high shear rate conditions.
  • High Temp. High Shear Rate Viscosity at 150°C (HTHS) – The high temperature viscosity of an oil in high shear rate conditions.
  • Sulfated Ash – The metallic ash content of an oil after it burns. This is a part of how to evaluate an oil’s cleanliness.
  • Acid Number – The acidity of an oil. This is sometimes referred to as Total Acid Number.
  • Base Number – The alkalinity of an oil. This is sometimes referred to as Total Base Number.
  • Evaporative Loss – The mass of oil that will evaporate at a specified temperature. This relates to oil consumption rate and an oil’s viscosity stability.
  • Foaming TendencyThe resistance an oil has to a head of foam both forming and persisting on its surface measured at three different temperature conditions.
  • Shear StabilityThe resistance for an oil’s molecules to be sheared or reduced. This property relates to viscosity stability.
  • Color – I sincerely hope this needs no description
  • Elemental Analysis A quantitative measurement of the concentration of chemical elements in a material. Phosphorus is the only element that is controlled or limited by JASO.
  • Infrared Absorption Spectrum Analysis (IR Scan) – A type of scan that identifies chemical bonds.
Figure 5: Example of an IR scan
Figure 6: Example of an IR scan

       If any of the descriptions of the tests are lacking for you and you are confused as to what it means, check the site glossary for a more in depth description. If you are still left unsatisfied, leave a comment or send me an email and I will do all that is in my power to explain it to you personally.

      You may have noticed that most of the tests on this list are only reported to JASO and don’t actually have any required values. This is because many of these tests are simply used as identifiers. JALOS periodically does “secret shopper” testing and pulls products off the shelves to make sure that the oil being sold complies with what was filed with JALOS. This has the dual purpose of ensuring that the originally filed results were accurately reported and that formula changes were not performed without requalifying the oil with JALOS. With so many different properties being reported, it would be easy to identify a simple manufacturing variance compared to an actual formula change, so it effectively keeps lubricant marketers from being dishonest when advertising a JASO registration.

    So that is the entire JASO 4-stroke engine oil specification minus the labeling requirements and then all it takes is a deposit of ¥40,000 (approximately $400) to the JALOS bank account to be added to their list and to display a JASO box such as the one below on the back label of an oil.

Figure 6: JASO registration box for rear labels of motorcycle engine oils.
Figure 7: JASO registration box for rear labels of motorcycle engine oils.

Only products that are officially registered with JASO and are included on the JASO filed engine oil list are permitted to display this box on their label so if you see the box, you should be able to look it up on the list to confirm its registration. You can also find the company that owns each formula and if you read the oil code you can tell exactly what country that product is manufactured in. By looking at digits two, three and four of the oil code, which are specified by a corresponding country code in Appendix 3 (Page 19) of the JASO T903:2011 specification document, you can tell the exact country of origin for every product on the list.

Figure 7: JASO oil code example.
Figure 8: JASO oil code example.

Why JASO is Important

Now you may be asking yourself, is registration really that important? It is true that registration is not required to market a product for 4-stroke motorcycle use, but the fact that a product is registered does give assurance from an independent third party that a product does perform as claimed. There are many many brands and products out there that claim to “meet JASO MA requirements” or they may say “meets JASO performance specifications” or something else along that same line. If there is only a claim and no box, then you simply need to take that company’s word for it that they comply, and if there is no official registration, it is only that company’s promise that they are formulating honestly. The products that claim to meet JASO requirements more than likely do, but there is certainly a higher chance that a company that does not register may not be testing to ensure that performance.

Registering with JASO does have a downside. It makes it difficult to improve formulas any more frequently than once every few years because of the cost involved for each reformulation, so it can make it difficult to adapt to quickly advancing technologies.

The JASO specifications give a benchmark for motorcycle specific oils that highlights the performance needs that are different from standard automotive oils. If you would like a reminder of those differences, the article “Motorcycle Specific Oil?” gives a quick overview of those needs. By addressing those differences and working with both motorcycle manufacturers and lubricant manufacturers, JASO continues to update the specification every five years or so to remain in step with the most up-to-date technologies; by keeping up-to-date with the technology advancements always happening, it makes sure that oils are able to advance without risking the loss of their JASO registration simply for trying to improve or do things maybe outside the ordinary to create a uniquely performing product.

What’s Next?


 The T903:2016 specification was released in April, 2016 and is now implemented. There was an attempt to bring in a new test to quantify gear protection, but there were problems validating the test procedure so it is not planned to go into effect until 2021 now.

The clutch test was revised to give a more accurate differentiation between the categories. So the updated ranges and test pieces now offer a more precise and useful test.

As mentioned above, gear pitting is an issue they want to address. It was not able to be implemented in the 2016 specification but it is still of interest for eventual inclusion into the specification.

The FZG Gear Test was the original test considered to analyze gear pitting performance. Unfortunately the FZG test method proposed for measuring pitting protection has been deemed too unreliable to be standardized. There is a lack of repeatability between laboratories performing the test and the cost of each test was determined to be too costly in the end.

An alternative test called the Thrust Needle Bearing Test has been suggested as an alternative to the FZG as an indicator of gear pitting protection. The test result has a close correlation to the FZG results and is very cheap to run relative to the FZG gear test. Unfortunately this test is also experiencing a lack of repeatability between laboratories at this time.

Unfortunately before the specification can include a new test, the test must display a strong correlation between facilities and a highly repeatable test method. Different users and laboratories must be able to obtain results within a reasonable margin of error, but until that happens, this new test will not be part of the specification. By 2021, they may have a new procedure developed that can work for this purpose.

       I already have a link to the JALOS website in the “Outside Links” page, but below this article you can find references directly to the JALOS documents regarding the JASO 4-stroke motorcycle engine oil specification. The full specification is publicly available though somewhat difficult to get through, so if you see something in there that was not adequately explained in this article, leave a comment on the article or send an email directly to Admin@mototribology.com with your question.

The JASO Registered 4-Stroke Engine Oil List

The JASO T903:2011 Specification

The JASO T903:2016 Specification

Read Part 2: 2-Strokes Here!