Most modern Harley-Davidson* Big Twin engines (Evolution, Twin Cam, Milwaukee‑Eight) have three separate sumps for the engine, transmission and the primary chaincase fluids. The transmission needs a fluid that protects gears and bearings under heavy loads and promotes smooth shifting. The primary needs the right friction properties for the wet clutch, plus protection for the chain and compensator bearing.
AMSOIL gives you two options: one oil for all three sumps, or dedicated fluids for the engine, transmission and primary. Here’s how each option works and how to choose.
Option 1: One oil for the engine, transmission and primary
AMSOIL 20W-50 100% Synthetic V-Twin Motorcycle Oil is specifically formulated for maximum performance and protection in engines, transmissions and primary chaincases, so you can conveniently use one fluid for all three sumps. It’s shear stable and resists thinning from mechanical activity, and it performs like a gear lube without the negative effects of extreme-pressure additives. It resists viscosity breakdown 6X better than Harley-Davidson Screamin’ Eagle* SYN3*1 for improved protection against compensator and transmission gear wear.
- Resists extreme heat to help keep engines clean
- Retains viscosity for excellent wear protection
- Convenience of one lubricant for all three sumps.
- Contains specialsumps-rust agents and passes the ASTM D1748 humidity cabinet rust test
- Warranty Secure™, keeping your factory warranty intact
1Based on testing of AMSOIL 20W-50 Synthetic V-Twin Motorcycle Oil and Harley-Davidson Screamin’ Eagle SYN3 purchased on 1/26/24 in the CEC L45-KRL, ASTM D445 test.
Option 2: Dedicated transmission and primary fluids
Some riders prefer to use lubricants specifically labeled for each sump, so AMSOIL also offers dedicated fluids for the transmission and primary chaincase. Both are 100% synthetic, Warranty Secure and cost-effective, high-performance alternatives to original equipment manufacturer (OEM) fluids. They are perfect for use in Harley-Davidson, Triumph* and pre-2013 Indian* motorcycles with separate lubricant sumps.
AMSOIL 100% Synthetic V-Twin Transmission Fluid
AMSOIL 100% Synthetic V-Twin Transmission Fluid forms a durable oil film on bearings and gears, which helps dampen loud thunks when shifting and reduce gear noise. It resists viscosity loss from shear and withstands extreme heat, while extreme-pressure additives add protection against wear and shock loading.
- Protects against gear and bearing wear
- Delivers smooth shifts
- Helps eliminate loud thunks and gear noise
AMSOIL 100% Synthetic V-Twin Primary Fluid
AMSOIL 100% Synthetic V-Twin Primary Fluid uses a balanced additive system that meets or exceeds the JASO MA/MA2 standard for consistent clutch performance and feel, in stop-and-go traffic or on the highway. Its load-holding capacity helps prevent clutch slip, and a heavy dose of anti-wear additives protects the chain, gears and compensator bearing.
- Delivers consistent clutch feel for confident starts
- Helps prevent clutch slip
- Provides smooth acceleration
- Helps riders easily find neutral
- Protects compensator bearing, chain and gears against wear
Which should you choose?
Both options protect your bike. Choose by how you like to do maintenance:
- One oil: stock one product and service all three sumps with the a single product. 20W-50 Synthetic V-Twin Motorcycle Oil is the simplest way to go.
- Dedicated fluids: use a dedicated transmission fluid tuned to help reduce gear noise, and a primary fluid focused on smoother clutch feel.
Not sure what AMSOIL products are right for your bike? Quickly find everything you need in our AMSOIL Motorcycle Product Guide.
How often to change transmission and primary fluid
- V-Twin Transmission Fluid: up to 20,000 miles (32,200 km) or one year, whichever comes first.
- V-Twin Primary Fluid: up to 10,000 miles (16,000 km) or one year, whichever comes first.
- 20W-50 Synthetic V-Twin Motorcycle Oil: up to twice the motorcycle manufacturer’s change interval or one year, whichever comes first, in engines, transmissions and primary chaincases when used with an AMSOIL oil filter. In Big Twin Harley-Davidson transmissions, follow the Harley-Davidson recommended drain interval for synthetic oil of up to 20,000 miles (32,000 km) or one year.
Ready to do it yourself? Follow our step-by-step guides to a Harley-Davidson transmission oil change and a Harley-Davidson primary oil change.
This article is part of our Motorcycle Oil and Maintenance guide. See every article in the guide.
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AMSOIL Staff articles draw on the combined expertise of AMSOIL engineers, chemists, Technical Services specialists, technical writers and product marketers. Content is developed from AMSOIL data sheets, laboratory and field testing, oil-analysis results and more than 50 years of synthetic-lubricant development. Topics span automotive, diesel, powersports, marine, small-engine, agricultural and industrial equipment, covering lubrication fundamentals, maintenance practices, product selection and real-world customer experience.
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