Why you should NOT use car engine oil in your motorcycle engine!

As requested by Brad, a technical article on why you should NOT use car engine oil in your motorcycle engine!

Up to 1998 car oils had been used as the base for many motorcycle oils, so a bike owner would not have experienced problems at that time when using a car oil in his motorcycle. I know, because I used a car oil in my Honda XR 600R which I crossed Africa on in 1995. Solo from Cape Town to Egypt and back again, a 21 000 km journey (pics at the end). As car technology evolved over the years, the oils that cars needed changed and additives were added that weren’t good for motorcycle engines. This was especially the case for motorcycle gearboxes and clutches. Although these modifications were positive for use in cars, they were damaging to motorcycles. This was mainly due to the fact that, unlike most motorcycles, cars use a separate oil for the gearbox. Most motorcycles use one oil system for the engine, gearbox and wet clutch system, where the fluid used therefore needs to be non-friction modified.

Over the past 20 years, car engine oils had to be blended using more and more friction modifiers due to the ever increasing regulatory drive to reduce vehicle emissions and to improve on fuel economy. The purpose of a friction modifier in a combustion engine, is to lower the amount of friction, thereby gaining better fuel economy. Friction modifiers are mild anti-wear additives used to minimize light surface contact, such as sliding and rolling. These can also be referred to as boundary lubrication additives. These additives are used in lubricants to modify the coefficient of friction, hence the name, friction modifiers. This is mainly due to the fact that friction modifiers can prevent direct contact of the solid surfaces thereby reducing friction and wear. This in turn helps improve the fuel economy of the engine.

Friction modifiers include anti-wear (AW) and extreme pressure (EP) additives. Commonly used AW additives in lubricants are zinc dialkyldithiophosphates (ZDDP). Phosphorous, sulphur and molybdenum disulphide are used as (EP) additives. However, friction modifiers, although good for cars, are not good for motorcycles as these friction modifiers can cause clutches to slip at higher revs and cause gearbox pitting, specifically localised corrosion and the formation of micro-cracks. Also, oil used in motorcycle engines is required to run under far more intense conditions than in cars because the oil has to endure higher temperatures as well as higher engine speed (RPM) and a greater power density where power density is the amount of horsepower per litre of oil. These circumstances subject the oil to significant operating stresses. This excluding the fact that in applications where the same oil is used for lubrication of both the engine and transmission, the oil must have excellent shear stability. Otherwise your transmission will shear your once 10w-40 motor oil to a 10w30 and then a 10w-20 and so on…. Motorcycle oils must contain detergents, dispersants and anti-oxidants to offer protection from thermal and/or oxidative oil breakdown which can lead to varnish and deposit formation. They must also contain anti-foam agents to reduce oil foaming and air entrainment under high-speed and/or high-RPM operation. In other words, the manufacturing of modern motorcycle engine oils requires a balanced formulation approach.

In 1998 the Japanese Automotive Standards Organization (or JASO for short) developed a grading system for motorcycle oils. JASO was created as an alternative to the API specifications, as API (American Petroleum Institute) was not able to fulfil the requirements of the Japanese engines. Effectively, JASO came to the rescue of motorcycle engines all over the world. Called JASO T903, it was introduced as a globally recognized standard for 4-stroke motorcycle oils. It defines the required performance levels for satisfactory lubrication of the different motorcycle designs. JASO introduced specifications to solve these problems for motorcycles and to also provide better oil standards for modern Japanese engines. To make sure that the right oil is used, motorcycle manufacturers require the oil to meet one of these JASO standards. The grading system measured (amongst other things) an oils ability to resist clutch friction (or slippage) and protection offered against engine wear and pitting in the gear box.

The friction requirements categorise oils as either high friction JASO MA or low friction JASO MB and are central to the JASO four-stroke standard. JASO introduced 2 ratings for 4 stroke motorcycle oils:

JASO MA – This was the standard for single unit engines where the wet clutch, gearbox and engine used the same oil. JASO-MA oils don’t contain friction modifiers.

JASO MB – This lower standard was for bikes that use separate oils for the engine, clutch and gearbox (e.g. Harley Davidson’s and BMW’s).

Then in 2006, MA1 and MA2 were added as additional categories within the JASO MA specification. This specification was introduced for modern motorcycle engines. As well as being a higher standard of oil the JASO-MA2 approval means the oil is suitable for use in bikes with catalytic converters in the exhaust system.

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 and includes the clutch frictional properties needed for these motorcycles. These oils are also 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/performance 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

The JASO T 903:2023 Clutch Test Friction Properties (JASO MA 2) are as follows

Dynamic Friction Index (DFI) ≥1.50 and ≤2.50

Static Friction Index (SFI) ≥1.60 and ≤2.50

Stop Time Index (STI) ≥1.60 and ≤2.50

The significance of the indices above:

Dynamic Friction Index (DFI) – Measure of clutch feel and how progressively power transfers during clutch engagement

Static Friction Index (SFI) – Measure of closed clutch pack torque handling capacity – resistance to clutch slip under high-torque “break-away” conditions

Stop Time Index (STI) – Measure of how quickly the clutch engages

Although the above motorcycle oil specifications are by far the most important and recognised worldwide, 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. This is however, a subject for another day.

Ravenol motorcycle oils, are JASO MA2 T903:2016 (M049RAV173) approved. As can be seen by the licence number shown (in this case, M049RAV173 which is the licence number for RAVENOL Motobike 4-T Ester SAE 5W-40). Ravenol is approved by JASO and is not just a recommendation, like so many other oil companies show on their oil can (which you as the consumer are expected to believe and trust that the oil complies with the specification claimed).

SUMMARY

As mentioned before, the manufacturing of motorcycle engine oils requires a balanced formulation approach. And not all motorcycle oils are created equally well. However, it’s your bike and your hard-earned money, so only you can make the decision on whether or not to spend the extra money on a brand that provides peace of mind and state-of-the-art performance, or something else?

To see all the pictures mentioned in this article, head over to our Ravenol SA Facebook page!

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