Motorcycle Oil, Primary and Transmission Fluids
















Should Harley owners use just one or all three in their bikes. Amsoil explains the difference.

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 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 labeled for each area?

Amsoil offers some guidance in deciding what’s right for your bike

AMSOIL recommends AMSOIL 20W-50 Synthetic V-Twin Motorcycle Oil in the engine, transmission and primary chain-case on most Harleys (consult the Amsoil Motor Cycle Product Guide for specific recommendations).

20W-50 oil offers…

  • Convenience. Riders 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.

Amsoil formulates 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
• prevent corrosion during storage.

AMSOIL vs. Harley-Davidson Oil: Performance Test

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 chain-case. Its frictional properties are dialed-in to allow the clutch plates to engage and disengage without loading or slipping for smooth shifts.

Can I Trust One Motorcycle Oil in all Three Areas of My Bike?

Despite these benefits, some riders question the practice of using one lubricant in all three areas of their bike. Riders also have a difficult time accepting that one motor oil can also protect the transmission and primary chain-case.

For these riders, Amsoil offers:

• Synthetic V-Twin Transmission Fluid
• Synthetic V-Twin Primary Fluid









What are the Differences Between Motorcycle Oil, Primary Oil & Transmission

Synthetic V-Twin Transmission and Synthetic V-Twin Primary Fluid are formulated to protect just one area of your bike rather than three. This specificity allows AMSOIL to “over-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 provides some advantage in helping quiet noisy transmission gears and enabling smooth shifts.

The lubricant develops a slightly thicker fluid film on gears, which provides extra cushion to help diminish loud “thunks” and gear noise.

AMSOIL Synthetic V-Twin Primary Fluid is also “over-engineered” to protect primary chain-case components. Its viscosity is like an SAE 50 motor oil. Formulating it as a straight-weight lubricant naturally offers an advantage in shear stability over multi-viscosity lubricants. 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. It’s wet-clutch-compatible formulation meets JASO MA/MA2 requirements.

So, One Oil or All Three?

So, which is the better route for Harley owners? It depends on what you value.
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 in all three areas is the best choice.
For riders who prefer lubricants dialed-in for each area of their bikes and don’t mind a few extra bottles of oil lying around the garage, use our full line of V-twin lubricants.
Either way, you can’t go wrong.