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 using a test apparatus outlined in the methodology. Viscosity measurements are taken at the end of 15, 30 and 90 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.

During engine and transmission operation, air is introduced into the lubricating oil, which may produce foam. In severe cases, foam can increase wear, operating temperatures and oxidation. Oil is non-compressible, but when air passes through loaded areas, the bubbles can collapse and allow the metal surfaces to contact each other. In addition, the oil has a larger surface area exposed to oxygen when air is trapped in the oil, which promotes increased oxidation.

Higher operating speeds and gear systems in motorcycles increase the need for good foam control. While oil cannot prevent the introduc- tion of air, it can control foaming through the use of anti-foam additives.

To determine foaming characteristics, ASTM test methodology D-892 is used. The testing is divided into three individual sequences. In each sequence, air is bubbled through the oil for five minutes and the foam generated is measured in millimeters immediately following the test. At the end of the sequence, the oil is allowed to settle for 10 minutes and the remaining foam is meas- ured again. Both results are reported. The tem- perature is altered for each sequence. Sequence I is conducted at 24° C, Sequence II at 93.5° C and Sequence III after allowing the oil to cool back to 24° C.

The results show the levels of foam present for each sequence immediately following the five- minute bubbling process. In the SAE 40 group, Pennzoil Motorcycle Oil, Lucas High Performance, Royal Purple Max-Cycle and Bel- Ray EXS Superbike failed to meet the foaming requirements of JASO T903:2006 and ISO 24254:2007, which specify a minimum stan- dard of 10/50/10. In the SAE 50 group, Motul 7100 Ester, Bel-Ray V-Twin and Lucas High Performance failed to meet the standards.

Only AMSOIL had oils in both the SAE 40 and SAE 50 groups that exhibited zero mL foam after the five-minute bubbling process.

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This graph shows the initial oil viscosity and the viscosity after the shear test. The SAE J306 high-temperature viscosity requirements (shaded area) for SAE 90 gear lubes are between 13.5 centistokes (a unit of measure for viscosity designat- ed as cSt) and 18.49 cSt @ 100°C (212°F) maximum.

Lucas 75/90 Synthetic, at 22.35 cSt, and Royal Purple Max-Gear 75W-90, at 19.32 cSt, both exceed the maximum 18.49 cSt initial viscosity (red), failing the SAE J306 requirements for SAE 90 gear lubricants. All other gear lubricants were with- in the required high-temperature viscosity range prior to the KRL Shear Stability Test.

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AMSOIL Dominator Synthetic Racing Oil features an additive package heavily fortified with zinc and phosphorus for superior long-term wear protection. Designed for maximum durability, it ensures critical engine components are protected for the duration of the race. Dominator Synthetic Racing Oil’s superior additive technology provides unmatched durability in extreme conditions. In addition, its high levels of zinc and phosphorus additives make it ideal for street rods, muscle cars and other vehicles with flat-tappet cams.

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