Motorcycle Oil, Primary Fluid & Transmission Fluid: WHAT’S THE DIFFERENCE?

Author: AMSOIL USA / Chris Bergner  Date Posted:12 August 2019 

Some V-twin motorcycles, like modern Indian* and Victory* bikes, use a shared sump, meaning they use the same lubricant in the engine, transmission and primary chaincase. Most Harley-Davidson motorcycles, however, use a separate sump for each lubricant. This presents Harley owners with a choice: Use the same lubricant in all three areas of the bike, or use a separate lubricant formulated and labelled for each area.

For the record, AMSOIL recommends AMSOIL 20W-50 Synthetic V-Twin Motorcycle Oil (MCV) or AMSOIL 4T MC5 20W-50 100% Synthetic Performance Motorcycle Oil MC5 in the engine, transmission and primary chaincase on most Harleys (consult the Motorcycle Product Guide at for specific recommendations).


The Reasons behind this are:

• Convenience. Buy and install one lubricant. This reduces cost and results in fewer half-used bottles of oil lying around the garage.

• Simplicity. Remembering to buy one lubricant is far easier than remembering three.

• Great all-around performance in all three areas of the bike. We formulate 20W-50 Synthetic V-Twin Motorcycle Oil to be an excellent all-around lubricant. It delivers outstanding engine protection due to its proven ability to fight wear, reduce heat, maintain cleanliness and prevent corrosion during storage. Synthetic V-Twin Motorcycle Oil also boasts a shear-stable formulation. It resists viscosity loss despite the intense pressure and churning action of high rpm transmission gears, allowing it to deliver reliable transmission protection. Synthetic V-Twin Motorcycle Oil meets JASO MA/MA2 standards and is wet-clutch compatible for excellent performance in the primary chaincase. Its frictional properties are dialled-in to allow the clutch plates to engage and disengage without loading or slipping for smooth shifts. 

Despite these benefits, some riders question the practice of using one lubricant in all three areas of their bikes. These riders are precisely why we offer Synthetic V-Twin Transmission Fluid (MVT) and Synthetic V-Twin Primary Fluid (MVP).


So what are the differences?

In essence, Synthetic V-Twin Transmission Fluid and Synthetic V-Twin Primary Fluid are formulated to protect just one area of your bike rather than three. This specificity allows us to engineer each lubricant for its precise application. Synthetic V-Twin Transmission Fluid has a higher viscosity than 20W-50 Synthetic V-Twin Motorcycle Oil. A higher-viscosity, or “thicker,” lubricant can help quiet noisy transmission gears and enable smooth shifts. The lubricant develops a slightly thicker fluid film on gears, which provides cushion to help diminish loud “thunks” and gear noise.

Likewise, AMSOIL Synthetic V-Twin Primary Fluid is designed only to protect primary chaincase components. Its viscosity is similar to an SAE 50 motor oil. Formulating it as a straight-weight lubricant naturally offers an advantage in shear stability over other multi-viscosity lubricants. (AMSOIL 20W-50 Synthetic V-Twin Motorcycle Oil is absolutely shear stable and will not thin out from mechanical activity.) This helps the fluid remain thicker, which helps it cling to the compensator without being “flung off” as easily for maximum protection. In Harleys, the compensator acts as a shock absorber to prevent engine vibration from affecting the transmission. Compensator wear often leads to a knocking or ticking noise. Synthetic V-Twin Primary Fluid also clings well to the chain for excellent wear protection. And its wet-clutch-compatible formulation meets JASO MA/MA2 requirements.


One oil or three? So, which is the better route for Harley owners? 

For riders who desire the simplicity and convenience of using one lubricant for all three areas, Following our primary recommendation of 20W-50 Synthetic V-Twin Motorcycle Oil or AMSOIL 4T MC5 20W-50 100% Synthetic Performance Motorcycle Oil in all three areas is the best choice.

For riders who prefer lubricants dialled-in for each area of their bikes and don’t mind a few extra bottles of oil lying around the garage, Look towards our specialised V-twin lubricants,

AMSOIL Synthetic V-Twin Transmission Fluid & AMSOIL Synthetic V-Twin Primary Fluid

Either way, You can’t go wrong.

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