JASO Explained Part 2: 2-Stroke

JASO Explained2.1

JASO Explained PART 2:

JASO 2-Stroke Engine Oil Specification

     The brief history of JASO with regards to 4-stroke requirements was described in JASO Explained: Part 1 and a lot of the same reasons were given for the formation of the JASO M345 specification for 2-stroke oils as were given for the T903 specification. At the time, there was a lack of control for performance levels of available lubricants and JALOS decided to form a specification that was designed specifically for motorcycle applications in the void left by other standards being discontinued. This gave the OEMs a standard to specify for use in their products that ensured their machines would not fail from inadequate lubrication.

     Before the JASO M345:2003 specification, the National Marine Manufacturers Association TC-W performance level was created in the 1960’s but focused on outboard and marine engine oils. The American Petroleum Institute (API) released specifications from API TA to API TC throughout the years, but in 1994 JASO released the JASO FA, FB and FC specifications of varying performance levels. This release of new specifications was partly in response to the API discontinuing any progression to the API 2-stroke specifications ending with API TC in 1993. Specifications made by the International Standards Organization (ISO) are similar to the JASO specifications for 2T engine oils with some minor differences, and I’ll elaborate on those differences later in this article.

     Later on, JALOS introduced the JASO FD specification to advance lubricant technology to an even higher standard and at the same time made the FA specification obsolete. So the three levels of performance currently in place are FB, FC and FD according to the JASO M345:2003 specification.

     The JASO two-stroke specifications are important because they create a benchmark for minimum performance criteria for two-stroke oils. This particular category of products may just have the largest variety of properties and formulations in the motorcycle market. Many lubricant companies have their own methods for formulating 2-stroke oils and in doing so have developed many unique solutions to the main concerns of 2-cycle lubrication. However, regardless of how the performance is accomplished, what they need to accomplish is set by JASO in no uncertain terms.

Figure 1: JASO M345:2003 specification for 2-stroke engine oil performance

     The numbers for Lubricity, Initial Torque, Part Detergency, Exhaust Smoke and Exhaust Smoke Blocking are all index numbers associated with scores associated with performance in each category. For each one, the higher the number is, the better the performance in that category.

The general rule for the different performance levels is this:

  • FB corresponds to high lubricity performance but without any low-smoke technology.
  • FC meets the FB lubricity standards but also is a low-smoke lubricant.
  • FD corresponds to higher detergency properties than the other two grades, meets the lubricity requirements and has low smoke requirements.

     Most of the performance testing is performed using standard test engines and measured by part raters following the JPI-5S-34-91 rating manual. Part rating is a very exact method of evaluating engine parts after use to determine their condition and raters are highly trained to perform this duty. Each of the methods uses specific engines for evaluation.

Figure 2: JASO M345:2003 test methods and test engines
Figure 2: JASO M345:2003 test methods and test engines


  • The M340 test measures the lubricity and friction characteristics of the lubricant. Less friction means less heat generated from friction and may increase component life greatly by doing so. It may also contribute to lower wear, although this is not always the case as friction and wear are different and are often addressed by different parts of the formula.
  • The M341 test measures the detergency of the oil which corresponds to its ability to remove existing deposits and prevent new deposits from forming on internal engine parts.
  • The M342 test evaluates how much smoke is produced by an engine using the test oil. This test is partly for environmental reasons but also affects performance more than some people may be aware.
  • The M343 standard tells us what the exhaust smoke’s effect on engine performance is. With the exhaust system playing a big part in engine output in 2-cycle engines, soot and carbon buildup can affect that performance negatively if not controlled.
  • The sulfated ash measurement assesses the oil’s contribution to ash formation caused by metallic additives that cannot fully burn. Many 2T oils utilize “ash-less” additive systems to eliminate this issue, but they are not required so this measurement is important.
  • Flash point measures the temperature at which the volatile vapors given off by a lubricant are produced at a high enough concentration to ignite with a flame source. This may indicate how well an oil will burn or remain unburned in a combustion chamber. Many oils utilize solvents in their formulas which may give a low result not indicative of the actual lubricating oil so be aware that the reported flash point may not tell the whole story. I would recommend finding the flash point of a 2-stroke oil without its solvent component to get its true contribution to the combustion.
  • Kinematic Viscosity at 100°C is a measurement of the thickness or fluidity of the oil and contributes to film strength.

     The reason JASO M345 is in need of an upgrade is because of those two test engines used in Figure 2. The 2-cycle test engines themselves are being discontinued and spare parts are becoming difficult to source in order to keep those motors running at the necessary performance level. Without standardized parts from the manufacturers, the engines cannot be kept running in adequate condition for the tightly controlled JASO testing.

     New engines are being tested and evaluated for standardization, and the next update is scheduled to go into effect in April of 2018. The original plan was to update the specification with new test engines in April of 2016, JALOS announced that they were pushing back the launch date to 2018 due to repeatability problems. The Yamaha ET-1 engine is currently the leading candidate for inclusion, but testing is still underway to ensure compliance with the strict standards for the indexing of various properties measured by the JASO M345 specification.

Figure 3: Yamaha ET-1 engine. Photo source: http://global.yamaha-motor.com/business/pp/generator/220v-50hz/0-1/et-1/
Figure 3: Yamaha ET-1 engine. Photo source: http://global.yamaha-motor.com/business/pp/generator/220v-50hz/0-1/et-1/

     Because of the uncertainty in this engine’s ability to provide repeatable and reproducible results, the specification is being pushed back until its results can either be verified or a different test engine can be identified, so don’t expect anything new until 2018. It was unclear what kind of performance advancements the new specification would have incorporated before this delay, but it appears there is a plan to separate smaller displacement engines such as brush cutters, chainsaws and other handheld equipment from vehicles with separate criteria. For the time being though, engines and parts are still available for the current test engines so new lubricants can still be evaluated accordingly to the high standards that are already in place.

     Before I finish this article, I do want to briefly mention the differences between the JASO and the ISO specifications for 2T engine oils because it is a distinction worth mentioning.

Figure 4: ISO 13738 specification for 2-stroke engine oil performance

    The ISO L-EGD and JASO FD are the exact same performance specification. The differences between ISO and JASO are in the B and C specifications. The ISO L-EGB and L-EGC specifications each have an additional detergency requirement. This means the ISO L-EGB and L-EGC specifications require higher performance levels than the JASO equivalents, but most oils that meet JASO requirements will also meet the ISO requirements, so there is rarely a difference between an oil claiming ISO or JASO performance levels.

Review –

So after all that your head is probably spinning trying to figure out what all of that means. So to boil it all down I’ll end with a few main points:

  • The JASO specifications indicate increasing performance levels with FB, FC, and FD specifications.
  • The requirements include lubricating ability, cleanliness, smoke potential, and a few physical properties.
  • ISO and JASO are essentially the same with a few minor differences.
  • The performance specifications give machine manufacturers real and tangible minimum requirements to maintain their equipment and ensure high performance.
  • With these specifications, we can look at specific performance differences between products to determine which is the best for our machines without having to rely on uncertain performance claims by lubricant companies.

Useful Links –

JALOS M345:2003 Specification manual

JASO M345 Registered Lubricant List