Harley-Davidson Oil Recommendations


Synthetic Motor Oils

OW-40 (AFF)

Formula 4-Stroke Power Sports Synthetic Motor Oils

10W-40 (MCF)

SAE Synthetic Motorcycle Oil

20W-50 (MCV)

SAE Synthetic Motorcycle Oil

10W-40 (AMF)

Synthetic High Performance Motorcycle Engine Oil

20W-50 (AMV)

Synthetic High Performance Motorcycle Engine Oil


SAE 60 Synthetic Racing Oil

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 longetivity. 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.

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

1. Operational Speed

2. Compression Ratios

3. Horse Power / Displacement Density

4. Variable Engine Cooling

5. Multiple Lubrication Functionality

6. Inactivity

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.

The following paragraphs 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.

The testing used to evaluate the lubricants was done in accordance with American Society for Testing and Materials (ASTM) procedures. 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.

Viscosity Shear Stability

An oil's viscosity can 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. Oil 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, 36% of the oils dropped one viscosity grade to an SAE 30. Within the SAE 50 group, 40% 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.

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 of the oils in their respective groups. Torco T-4SR shared to a SAE 30 and Yamalube sheared to a 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 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 centipoises (cP), which are units of viscosity. The higher the test result, the greater the level of protection offered by the oil.


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 Pennzoil Motorcycle at 1,010 ppm, had identical 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 the lowest zinc level (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.