The Motorcycle Enthusiast

jewel of your harley

Willie G. Davidson calls it the “jewel” of Harley-Davidson motorcycle design – that distinctive V-twin engine that sits at the heart of every model. Since Co-founder and Chief Engineer Bill Harley designed the first H-D V-twin in 1909, some form of this legendary powerplant has been providing that unmistakable H-D look, sound, and feel for enthusiasts around the world.

Its looks have changed in 107 years since that first design – and the technology has advanced beyond Bill Harley’s wildest dreams – but its essence remains the same. It’s been often copied, but never duplicated. Only a Harley V-twin engine can do what it does.

In honor the new Milwaukee-Eight™ engine, here’s a look at some of its most significant predecessors.




Relevance: Significant increase in power and performance

New Technology: Four valves per cylinder; oil- or water-cooled cylinder heads

Fast Fact: The first Harley-Davidson motorcycle to feature eight valves per cylinder was the 1927 8-Valve Board Track Racer

Important Model: 2017 Electra Glide® Ultra Classic®




Relevance: First liquid-colled H-D engine design; introduced on all-new V-Rod

New Technology: Liquid cooling; anodized aluminum bodywork

Fast Fact: A great deal of thought and experimentation was put into the sound of the Revolution engine, to make sure the V-Rod still sounded like a Harley-Davidson® motorcycle

Important Model: 2002 VRSCA V-Rod®

twin cam


Twin Cam

Relevance: More displacement and power; advanced reliability

New Technology: Twin chain-driven camshafts; Twin Colling (2014 touring models)

Fast Fact: Along with numerous other Project RUSHMORE upgrades to the Touring family, the Twin Cam was part of the biggest product development project in Harley-Davidson history

Important Model: 2000 FXSSTD Softail® Deuce




Relevance: Sometimes called "the engine that saved Harley-Davidson," because it helped the Motor Company turn the corner after the famous 1981 AMF buyback

New Technology: Technology: Oil-tight design; reduced mechanical noise; aluminum heads and cylinders

Fast Fact: One of Harley-Davidson's own advertisements declared, "Thank God they don't leak oil anymore."

Important Model: 1984 FXST Softail




Relevance: Increased displacement, power

New Technology: New rocker boxes and rocker arms that pivot on shafts

Fast Fact: The name is derived from the shape of the heads, which are said to look like the back of an inverted coal shovel

Important Model: 1971 Super Glide®; 1977 Low Rider®; 1980 Wide Glide®




Relevance: Introduced on the first Sportster® model for 1957

New Technology: Overhead valve design; increased horsepower 

Fast Fact: The Sportster model as designed to be light, nimble, and fast, stripped of features such as saddlebags, luggage racks or extra lights

Important Model: 1957 Sportster




Relevance: New styling, technology

New Technology: More-efficient aluminum cylinder heads; quieter, low-maintenance hydraulic valve lifters

Fast Fact: Both bikes featured in the movie Easy Rider - the "Captain America" chopper and the "Billy Bike" - had Panhead engines

Important Model: 1948 FL




Relevance: More power; distinctive look, with two large rocker shaft bolts on each cylinder

New Technology: Overhead valves; first H-D® closed-loop recirculating oil system 

Fast Fact: Despite lack of initial dealer enthusiasm, grew to become an iconic (and very collectible) engine model

Important Model: 1936 EL




Relevance: Greater longevity; more power - in 45-, 74-, and (later) 81-inch displacements

New Technology: Side-valve for both intake and exhaust

Fast Fact: The Flathead is so called because the side-valve design allows the heads to be flat

Important Model: 1929 DL




Relevance: An improved version of the Atmospheric V-Twin Engine

New Technology: Mechanically operated valves for more consistent performance and reliability

Fast Fact: Served as the Motor Company's flagship engine for nearly two decades

Important Model: 1915 J Model



Atmospheric V-Twin

Relevance: First Harley-Davidson V-Twin engine design

New Technology: Twin cylinders created more efficient power; intake valves activated by vacuum created during intake stroke

Fast Fact: Established the air-cooled 45-degree v-twin engine as the bedrock of Harley-Davidson design

Important Model: 1909 Model 5-D