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Motorcycle Oil, Primary Fluid & Transmission Fluid: What’s The Difference?

Oil Debate on V-Twin motors requiring three sumps

The Fool Said I Can Use 20W-50 In All Three. What?

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 (Don’t forget about Davidson) 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. Here, we offer guidance for deciding what’s right

For the record, AMSOIL recommends AMSOIL 20W-50 Synthetic V-Twin Motorcycle Oil (MCV) in the engine, transmission and primary chaincase on most Harleys (consult the Motorcycle Product Guide at amsoil.com for specific recommendations). It 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.
  • It’s what the upper brass at AMSOIL use in their bikes.

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.

See why the 50 weight qualifies as a 90 in the transmission. 

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 dialed-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. They have a difficult time accepting that a motor oil can also protect the transmission and primary chaincase.

I don’t think so. My Mechanic always said you have to use different oils.  – That’s partially true…

If you believe this to not be true we make the separates for you. Debate free oil options! And yes, they are more dialed in.. This is why we offer Synthetic V-Twin Transmission Fluid (MVT) and Synthetic V-Twin Primary Fluid (MVP).

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.

Transmission Fluid

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.

Again, we realize that’s what people want and in some cases it’s beneficial to the gears but it’s slightly thicker than the OEM specifications or better put – on the high side of the range. The only real downside other than cost is less efficiency in cooler weather and a change in overall MPG.

Primary Fluid

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.

Many buy this because some bikes have issues shifting back to neutral. AMSOIL Primary Oil makes it much easier for the linkage to catch neutral when you need it.

One oil or three?

So, which is the better route for Harley owners? Either way you can’t go wrong but examine if you identify with the issues requiring the 2nd choices.

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, steer them toward our full line of V-twin lubricants.

Either way, they can’t go wrong. 

Ordering 605-274-2580

Can Your Motor Oil Handle the Seven Responsibilities of a Lubricant?

Spring Oil Change

Can Your Motor Oil Handle the Seven Responsibilities of a Lubricant?

Most motorists understand the primary functions of motor oil: reduce friction and wear. However, motor oil and other lubricants must do more to protect your vehicles and equipment. With engines and equipment becoming more powerful and sophisticated, it takes a properly formulated, well-balanced lubricant to carry out these seven critical functions.


• Minimize Friction

Lubricants reduce contact between components, minimizing friction and wear.

• Clean

Lubricants maintain internal cleanliness by suspending contaminants within the fluid or by preventing the contaminants from adhering to components. Base oils possess a varying degree of solvency that assists in maintaining internal cleanliness. Solvency is the ability of a fluid to dissolve a solid, liquid or gas. While the solvency of the oil is important, detergents and dispersants play a key role. Detergents are additives that prevent contaminants from adhering to components, especially hot components such as pistons or piston rings. Dispersants are additives that keep contaminants suspended in the fluid. Dispersants act as a solvent, helping the oil maintain cleanliness and prevent sludge formation.

• Cool

Reducing friction minimizes heat in moving parts, which lowers the overall operating temperature of the equipment. Lubricants also absorb heat from contact surface areas and transport it to a location to be safely dispersed, such as the oil sump. Heat-transfer ability tends to be a trait of the base oil’s thickness – lighter oils tend to transfer heat more readily.

• Seal

Lubricants act as a dynamic seal in locations like piston rings and cylinder contact areas to prevent contamination.

• Dampen Shock

A lubricant can cushion the blow of mechanical shock. A highly functional lubricant film can resist rupture and absorb and disperse these energy spikes over a broad contact area. As the mechanical shock to components is dampened, wear and damaging forces are minimized, extending the component’s overall operating life.

• Protect

A lubricant must have the ability to prevent or minimize internal component corrosion. Lubricants accomplish this either by chemically neutralizing corrosive products or by forming a barrier between the components and the corrosive material.

• Transfer Energy

Because lubricants are incompressible, they can act as an energy-transfer medium, such as in hydraulic equipment or valve lifters in an automotive engine.

Lubricants do far more than simply protect against wear. High-quality lubricants – like AMSOIL synthetic lubricants – are formulated to excel in each of these critical areas, ensuring you get the most out of your vehicles and equipment.