The Milwaukee-Eight engine is a game-changer for Harley-Davidson, marking the ninth generation of its iconic Big Twin engines. Introduced in 2017, it replaced the aging Twin Cam motor, which had been in production since 1998. This new engine was designed to meet stringent global emissions standards while delivering the performance enthusiasts crave.
The name Milwaukee-Eight is a nod to Harley-Davidson's corporate headquarters in Wisconsin and the number of valves in the engine. With four valves per cylinder, this design breaks away from the traditional two-valve pushrod engine architecture that defined Harley-Davidson motors for decades.
Mechanically, the Milwaukee-Eight retains the classic 45-degree V-twin format but features a completely redesigned valvetrain. The single chain-driven camshaft reduces mechanical clatter and friction compared to the dual camshafts used in the outgoing Twin Cam engine.
The camshaft operates four valves via forked rocker arms, providing a more efficient airflow path for the massive twin cylinders. This design also enables Harley-Davidson to achieve significantly improved volumetric efficiency and effective thermal management strategies.
Harley initially launched the Milwaukee-Eight with two displacements: a standard 107-cubic-inch engine and a massive 114-cubic-inch version reserved for its range-topping CVO models. In 2019, the bikemaker introduced the larger Milwaukee-Eight 117, and in 2023, an even larger Milwaukee-Eight 121 VVT featuring variable valve timing.
The Milwaukee-Eight is arguably Harley-Davidson's most advanced air-cooled engine, thanks to its improved airflow and thermal management. The four-valve cylinder head increases intake and exhaust valve airflow by a whopping 50% over the previous Twin Cam engine, allowing for more efficient combustion across the massive bore of the giant twin cylinders.
To ensure complete combustion, the Milwaukee-Eight engine features a dual-ignition system with two spark plugs per cylinder. This results in faster and more complete air-fuel mixture burn, which helps reduce emissions and prevents pre-detonation or engine knock.
Cooling was a critical engineering focus during the development of the Milwaukee-Eight, so the engine uses targeted cooling in the cylinder heads. Depending on the engine configuration, you may receive 'precision oil cooling' or 'twin-cooling', both designed to keep temperatures under control and ensure optimal performance.
