A Study of Motorcycle Oils Amsoil Power Sports Group © March 2006, AMSOIL INC. Download a Free Copy of this Report
TABLE OF CONTENTS Overview Purpose Method Scope Review Candidates Physical Properties, Performance Results, and Prices      SAE Viscosity Grade (Initial Viscosity - SAE J300)      Viscosity Index (ASTM D-2270)      Viscosity Shear Stability (ASTM D-6278)      High Temperature / High Shear Viscosity (HT/HS ASTM D-5481)      Zinc Concentration (ppm, ICP)      Wear Protection (4-Ball, ASTM D-4172)      Gear Performance (FZG ASTM D-5182)      Oxidation Stability (TFOUT ASTM D-4742)      Volatility (Evaporation) (ASTM D-5800)      Acid Neutralization and Engine Cleanliness (TBN ASTM D-2896)      Foaming Tendency (ASTM D-892)      Rust Protection (Humidity Cabinet ASTM D-1748)      Pricing      Wet-Clutch Compatibility (JASO T 904-98, limited review) Scoring and Summary Results Conclusion Appendix A      Affidavit of Test Results      References

Overview

Motorcycles have long been used as a popular means of general transportation as well as for recreational use. There are nearly five million registered motorcycles in the United States, with annual sales in excess of three-quarters of a million units. This trend is unlikely to change. As with any vehicle equipped with an internal combustion engine, proper lubrication is essential to insure performance and longevity. It is important to point out that not all internal combustion engines are similarly designed or exposed to the same types of operation. These variations in design and operation place different demands on engine oils. Specifically, the demands placed on motorcycle engine oils are more severe than those placed on automotive engine oils. Therefore, the performance requirements of motorcycle oils are more demanding as well.

Though the degree may be debatable, few will disagree that a difference exists between automotive and motorcycle applications. In which area these differences are and to what degree they alter lubrication requirements are not clear to most motorcycle operators. By comparing some basic equipment information, one can better understand the differences that exist.

The following comparison information offers a general synopsis of both automotive and motorcycle applications.

There are six primary differences between motorcycle and automotive engine applications:

1. Operational Speed - Motorcycles tend to operate at engine speeds significantly higher than automobiles. This places additional stress on engine components, increasing the need for wear protection. It also subjects lubricating oils to higher loading and shear forces. Elevated operating RPMs also promote foaming, which can reduce an oil's load-carrying ability and accelerate oxidation.
2. Compression Ratios - Motorcycles tend to operate with higher engine compression ratios than automobiles. Higher compression ratios place additional stress on engine components and increase engine operating temperatures. Higher demands are placed on the oil to reduce wear. Elevated operating temperatures also promote thermal degradation of the oil, reducing its life expectancy and increasing the formation of internal engine deposits.
3. Horse Power / Displacement Density - Motorcycle engines produce nearly twice the horsepower per cubic inch of displacement of automobile engines. This exposes the lubricating oil to higher temperatures and stress.
4. Variable Engine Cooling - In general, automotive applications use a sophisticated water-cooling system to control engine operating temperature. Similar systems can be found in motorcycle applications, but other designs also exist. Many motorcycles are air-cooled or use a combination air/oil design. Though effective, they result in greater fluctuations in operating temperatures, particularly when motorcycles are operated in stop-and-go traffic. Elevated operating temperature promotes oxidation and causes oils to thin, reducing their load carrying ability.
5. Multiple Lubrication Functionality - In automotive applications, engine oils are required to lubricate only the engine. Other automotive assemblies, such as transmissions, have separate fluid reservoirs that contain a lubricant designed specifically for that component. The requirements of that fluid differ significantly from those of automotive engine oil. Many motorcycles have a common sump supplying oil to both the engine and transmission. In such cases, the oil is required to meet the needs of both the engine and the transmission gears. Many motorcycles also incorporate a frictional clutch within the transmission that uses the same oil.
6. Inactivity - Motorcycles are typically used less frequently than automobiles. Whereas automobiles are used on a daily basis, motorcycle use is usually periodic and in many cases seasonal. These extended periods of inactivity place additional stress on motorcycle oils. In these circumstances, rust and acid corrosion protection are of critical concern.

It is apparent that motorcycle applications place a different set of requirements on lubricating oils. Motorcycle oils, therefore, must be formulated to address this unique set of high stress conditions.

Purpose

The purpose of this paper is to provide information regarding motorcycle applications, their lubrication needs and typical lubricants available to the end user. It is intended to assist the end user in making an educated decision as to the lubricant most suitable for his or her motorcycle application.

Method

The testing used to evaluate the lubricants was done in accordance with American Society for Testing and Materials (ASTM) procedures. Test methodology has been indicated for all data points, allowing for duplication and verification by any analytical laboratory capable of conducting the ASTM tests. A notarized affidavit certifying compliance with ASTM methodology and the accuracy of the test results is included in the appendix of this document.

Scope

This document reviews the physical properties and performance of a number of generally available motorcycle oils. Those areas of review are:

1. An oil's ability to meet the required viscosity grade of an application.
2. An oil's ability to maintain a constant viscosity when exposed to changes in temperature.
3. An oil's ability to retain its viscosity during use.
4. An oil's ability to resist shearing forces and maintain its viscosity at elevated temperatures.
5. An oil's zinc content.
6. An oil's ability to minimize general wear.
7. An oil's ability to minimize gear wear.
8. An oil's ability to minimize deterioration when exposed to elevated temperatures.
9. An oil's ability to resist volatilization when exposed to elevated temperatures.
10. An oil's ability to maintain engine cleanliness and control acid corrosion.
11. An oil's ability to resist foaming.
12. An oil's ability to control rust corrosion.

Individual results have been listed for each category. The results were then combined to provide an overall picture of the ability of each oil to address the many demands required of motorcycle oils.

Review

Two groups of candidate oils were tested, SAE 40 grade oils and SAE 50 grade oils. The oils tested are recommended specifically for motorcycle applications by their manufacturers.

Physical Properties, Performance Results, and Prices

SAE Viscosity Grade (Initial Viscosity - SAE J300)

A lubricant is required to perform a variety of tasks. Foremost is the minimization of wear. An oil's first line of defense is its viscosity (thickness). Lubricating oils are by nature non-compressible and when placed between two moving components will keep the components from contacting each other. With no direct contact between surfaces, wear is eliminated. Though non-compressible, there is a point at which the oil film separating the two components is insufficient and contact occurs. The point at which this occurs is a function of an oil's viscosity. Generally speaking, the more viscous or thicker an oil, the greater the load it will carry. Common sense would suggest use of the most viscous (thickest) oil. However, high viscosity also presents disadvantages. Thicker oils are more difficult to circulate, especially when an engine is cold, and wear protection may be sacrificed, particularly at start-up. Thicker oils also require more energy to circulate, which negatively affects engine performance and fuel economy. Furthermore, the higher internal resistance of thicker oils tends to increase the operating temperature of the engine. There is no advantage to using an oil that has a greater viscosity than that recommended by the equipment manufacturer. An oil too light, however, may not possess sufficient load carrying ability to meet the requirements of the equipment.

From a consumer standpoint, fluid viscometrics can be confusing. To ease selection, the Society of Automotive Engineers (SAE) has developed a grading system based on an oil's viscosity at specific temperatures. Grading numbers have been assigned to ranges of viscosity. The equipment manufacturer determines the most appropriate viscosity for an application and indicates for the consumer which SAE grade is most suitable for a particular piece of equipment. Note that the SAE grading system allows for the review of an oil's viscosity at both low and high temperatures. As motorcycle applications rarely contend with low temperature operation, that area of viscosity is not relevant to this discussion.

The following chart identifies the viscosities of the oils before use. The purpose of testing initial viscosity is to ensure that the SAE grade indicated by the oil manufacturer is representative of the actual SAE grade of the oil, and that it is therefore appropriate for applications requiring such a fluid. The results were obtained using American Society for Testing and Materials (ASTM) test methodology D-445. The fluid test temperature was 100° C and results are reported in centistokes. Using SAE J300 standards, the SAE viscosity grades and grade ranges for each oil were determined and are listed below.

The results show that all of the oils tested except Lucas High Performance Motorcycle 10W-40 have initial viscosities consistent with their indicated SAE viscosity grades. Those oils consistent with their indicated SAE viscosity grades are appropriate for use in applications recommending these grades/viscosities.

Viscosity Index (ASTM D-2270)

The viscosity (thickness) of an oil is affected by temperature changes during use. As the oil's temperature increases, its viscosity will decrease along with its load carrying ability. The degree of change that occurs with temperature is determined by using ASTM test methodology D-2270. Referred to as the oil's Viscosity Index, the methodology compares the viscosity change that occurs between 100° C (212° F) and 40° C (104° F). The higher the viscosity index, the less the oil's viscosity changes with changes in temperature. While a greater viscosity index number is desirable, it does not represent that oil's high temperature viscosity or its load carrying ability. Shearing forces within the engine, and particularly the transmission, can significantly reduce an oil's viscosity. Therefore, oils with a lower viscosity index but higher shear stability (discussed below) can, in fact, have a higher viscosity at operating temperature than one with a higher viscosity index and lower shear stability.

Viscosity Shear Stability (ASTM D-6278)

An oil's viscosity can also be affected through normal use. Mechanical activity creates shearing forces that can cause an oil to thin out, reducing its load carrying ability. Engines operating at high RPMs and those that share a common oil sump with the transmission are particularly subject to high shear rates. Gear sets found in the transmissions are the leading cause of shear-induced viscosity loss in motorcycle applications.

The ASTM D-6278 test methodology is used to determine oil shear stability. First an oil's initial viscosity is determined. The oil is then subjected to shearing forces at 30 cycle intervals. Viscosity measurements are taken at the end of 30, 90 and 120 cycles and compared to the oil's initial viscosity. The oils that perform well are those that show little or no viscosity change. Oils demonstrating a significant loss in viscosity would be subject to concern. The flatter the line on the charts below, the greater the shear stability of the oil. Each SAE grade was split into two or more groups to make the charts easier to reference.

The results point out significant differences between oils and their ability to retain their viscosity. Within the SAE 40 group, 41.6% of the oils dropped one viscosity grade to an SAE 30. Within the SAE 50 group, 43.8% dropped one grade to an SAE 40. Most of the oils losing a viscosity grade did so quickly, within the initial 30 cycles of shearing. Testing revealed that Lucas 10W-40 High Performance Motorcycle oil was the only oil to shear to an SAE 20.

It should be noted that both high and low viscosity index oils exhibited significant amounts of shear and viscosity loss. Two of the oils with the highest viscosity index, Torco T-4SR in the SAE 40 group and Yamalube 4R in the SAE 50 group, had the largest drops in viscosity of all the oils in their respective groups. Torco T-4SR sheared to an SAE 30 and Yamalube sheared to an SAE 40. Valvoline 4-Stroke SAE 50 and Castrol V-Twin SAE 50 had a comparatively low viscosity index and they too lost significant viscosity, shearing down to an SAE 40.

High Temperature / High Shear Viscosity (HT/HS ASTM D-5481)

Shear stability and good high temperature viscosity are critical in motorcycle applications. How these two areas in combination affect the oil is measured using ASTM test methodology D-5481. The test measures an oil's viscosity at high temperature under shearing forces. Shear stable oils that are able to maintain high viscosity at high temperatures perform well in the High Temperature/High Shear Test. The test is revealing as it combines viscosity, shear stability and viscosity index. It is important because bearings require the greatest level of protection during high temperature operation. Test results are indicated in cetipoises (cP), which are units of viscosity. The higher the test result, the greater the level of protection offered by the oil.

Zinc Concentration (ppm, ICP)

Though viscosity is the most critical variable in terms of wear protection, it does have limitations. Component loading can exceed the load carrying ability of the oil. When that occurs, partial or full contact results between components and wear will occur. Chemical additives are added to the oil as the last line of defense to control wear in these conditions. These additives have an attraction to metal surfaces and create a sacrificial coating on engine parts. If contact occurs the additive coating takes the abuse to minimize component wear. The most common additive used in internal combustion engine oils is zinc dithiophosphate (ZDP). A simple way of reviewing ZDP levels within an oil is to measure the zinc content. It should be noted that ZDP defines a group of zinc-containing compounds that vary in composition, quality and performance. Quantity of zinc content alone does not indicate its performance. Therefore, it cannot be assumed that oils with higher concentrations of zinc provide better wear protection. Additional testing must be reviewed to determine an oil's actual ability to prevent wear. The tables below show the levels of zinc present in each of the oils. Results were determined using an inductively coupled plasma (ICP) machine and are reported in parts per million.

Zinc levels varied widely in both the SAE 40 and 50 groups, ranging from as low as 860 ppm to as high as 2,465ppm.

Wear Protection (4-Ball, ASTM D-4172)

The ASTM D-4172 4-Ball Wear Test is a good measure of the existence and robustness of an oil's additive chemistry. It is used to determine an oil's ability to minimize wear in case of metal-to-metal contact. The test consists of a steel ball that sits atop three identical balls that have been placed in a triangular pattern and restrained from moving. All four balls are immersed in the test oil, which is heated and maintained at a constant temperature. The upper ball is then rotated and forced onto the lower three balls with a load measured in kilogram-force (kgf). After a one-hour period of constant load, speed and temperature, the lower three balls are inspected at the point of contact. Any wear will appear as a single scar on each of the lower balls. The diameter of the scar is measured on each of the lower balls and the results are reported as the average of the three scars, expressed in millimeters. The lower the average scar diameter, the better the wear protection of the oil. In this case, the load, speed and temperature used for the test were 40 kg, 1800 RPMs and 150° C respectively.

Interestingly, the SAE 40 oils with the highest and lowest levels of zinc, Maxima Maxum 4 at 2,464 ppm and Lucas High Performance Motorcycle at 860 ppm, had similar mid-range results. Royal Purple, with an average level of zinc (1,474 ppm) had the largest wear scar (nearly 55% larger than the next closest wear scar size). Zinc levels for those oils performing the best, AMSOIL MCF, Mobil 1 MX4T, Motul 300V Sport and Torco T-4SR ranged from 1,061 to 1,762 ppm.

The SAE 50 group showed a similar trend. Golden Spectro 4, with the highest zinc level (2,162 ppm), performed less than average in the 4-Ball Wear Test, while the Motul 300 V Competition, with one of the lowest zinc levels (1,048 ppm), tied with AMSOIL MCV and Torco T-4SR with the best test results.

The results strongly suggest that simply having high levels of zinc is not sufficient to effectively minimize wear.

Gear Performance (FZG ASTM D-5182)

Wear protection is provided by both the oil's viscosity and its chemical additives. The greatest need for both is in the motorcycle transmission gear set. High sliding pressures, shock loading and the shearing forces applied by the gears demand a great deal from a lubricant. Motorcycle applications present a unique situation because many motorcycle engines share a common lubrication sump with the transmission. The same oil lubricates both assemblies, yet engines place different demands on the oil than do transmissions. What may work well for one may not work well for the other. In an attempt to meet both needs, a lubricant's performance can be compromised in both areas.

To examine gear oil performance, the ASTM test methodology D-5182 (FZG) is used. In this test, two hardened steel spur gears are partially immersed in the oil to be tested. The oil is maintained at a constant 90° C and a predetermined load is placed on the pinion gear. The gears are then rotated at 1,450 RPM for 21,700 revolutions. Finally, the gears are inspected for scuffing (adhesive wear). If the total width of wear on the pinion gear teeth exceeds 20 mm, the test is ended. If less than 20 mm of wear is noted, additional load is placed on the pinion gear and the test is run for another 21,700 revolutions. Each time additional load is added, the test oil advances to a higher stage. The highest stage is 13. Results indicate the stage passed by each oil. Wear is reported for the stage at which the oil failed.

The test shows that 58.3% of the SAE 40 grade oils and 75% of the SAE 50 grade oils passed stage 13. Note that in the SAE 40 group, Mobil 1 MX4T, Motul 300V Sport and Torco T-4SR tied with AMSOIL MCF for the best 4-ball result but scored among the lowest in the FZG gear test. In the SAE 50 group, Motul 300V Competition and Torco T-4SR tied with AMSOIL MCV for the best 4-ball result, yet scored among the lowest in the remaining 25%. FZG and 4-ball wear tests measure wear protection differently. High scores in both tests indicate superior wear protection in a variety of applications and conditions. Only AMSOIL MCF (SAE 40) and MCV (SAE 50) placed on top in both wear tests.

Oxidation Stability (TFOUT ASTM D-4742)

Heat can destroy lubricants. High temperatures accelerate oxidation, which shortens the oil life and promotes carbon deposits. Oxidized lubricants can create and react with contaminants such as fuel and water to produce corrosive by-prod-ucts. Oxidation stability is critical in air-cooled and high performance motorcycles.

ASTM test methodology D-4742 is used to determine an oil's ability to resist oxidation by exposing the oil to common conditions found in gasoline fueled engines. These conditions include the presence of fuel; metal catalysts such as iron, lead and copper; water; oxygen and heat. Typically, the initial rate of oxidation is slow and increases with time. At a certain point, the rate of oxidation will increase significantly. The length of time it takes to reach that level of rapid oxidation is measured in minutes.

The test shows that 50% of the SAE 40 group oils and only 37.5% of the SAE 50 group oils achieved the maximum obtainable results of 500 minutes. The results of the remaining oils suggest a faster rate of degradation and shorter service life.

Superior oxidation stability is obtained through a combination of oil base stock and additive technology. In addition to being an anti-wear agent, zinc dithiophosphate (ZDP) is also an oxidation inhibitor. Similar to the discussion on wear, one might assume that oils with higher levels of zinc would provide improved oxidation stability. However, the results show that high ZDP levels were not consistent with good oxidation stability in the TFOUT test.

Volatility (Evaporation) (ASTM D-5800)

When oil is heated, lighter fractio