Detailed Development of Harley-Davidson’s Milwaukee-Eight Engine
Innovation and experience set the standard for the next generation of V-Twin motors.
Highway Needs
The development of Harley-Davidson's Big Twin motor and America's interstate highways follow a similar trajectory. As roads improved, so did the demand for cooler, faster-running engines. Meeting those same requirements today is the Milwaukee-Eight — Harley-Davidson's latest Big Twin. Here is a look at the research and development of the Motor Company's best powerplant to date.
Cool Configuration
Released with the 2017 touring lineup, the Milwaukee-Eight was offered in 107 and 114 cubic-inch configurations. The 'M8' 107 stuck to the familiar air-cooled top end with the addition of a factory-installed oil-cooler. A 'Twin-Cooled' version, featuring liquid-cooled heads and radiators, was installed in the Ultra Limited, Road Glide Ultra, and the TriGlide. The beefy 114 M8 found its way into CVO models and the Limited.
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Brand-New Motor
Alex Bozmoski, Chief Engineer of New Products at Harley-Davidson spoke about the new Milwaukee-Eight in a Cycle World Magazine interview in 2017. He stated, “It’s a brand-new motor, tip to tail.” With over thirty years of experience on the Evolution and Twin Cam motors, Bozmoski is something of an expert. More than just new, the M8 is a real accomplishment and offers advanced engineering wrapped in a classic V-Twin package.
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Valve Count
The Milwaukee-Eight might be a completely new piece of engineering, but it borrows from the past. The 'Eight' in its name refers to the total number of valves — a configuration not found on a Harley-Davidson motor since the 1920s and board-track racing motors. The end goal of the increased valve count was better cooling. Visible here is the dual spark plug setup and the shallow four-valve combustion chamber.
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Two-Up Power
While the cooler operation was one goal, the performance was the other. The eight-valve engine makes great power and torque yet manages to be emissions-compliant, fuel-efficient, and highly reliable. The Milwaukee-Eight's development was informed by exhaustive research. Known as the 'Voice of the Customer,' one thousand riders in seven cities were surveyed. The unanimous feedback was more power for two-up riding and a cooler-running engine.
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Heat Management
The Milwaukee-Eight manages to deliver liquid-cooling while keeping the iconic look of a finned air-cooled engine. Harley-Davidson called this approach 'strategic cooling.' Project Rushmore, the Motor Company's 2014 customer-driven improvement initiative, used the same approach with select Twin Cam engines. Liquid coolant passages were added to the exhaust valve seats. Cooler, better sealing valves directly translates to power gains.
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Simple Design
Unlike the Twin Cam, the Milwaukee-Eight returns to a single camshaft design. The new four-lobe camshaft is chain-driven with an automatic hydraulic tensioner. Fewer moving parts mean reduced noise and lower internal friction. While gear-driven cams are more precise, chains are simpler and quieter. Bozmoski compared the approach to the Evolution engine design. He whimsically put it, “We’re killing the noise so we can keep the music.”
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Iconic Goals
Willie G. Davidson asked the development team to make something worthy of the iconic 'Engine Wall' at the Harley-Davidson Museum. Brad Richards, Vice President of Styling & Design at Harley-Davidson said that one of his primary concerns was to have the engine “visually spilling out of the motorcycle.” With its sculpted rocker boxes and tapered cylinder heads, the Milwaukee-Eight achieves these goals. It will no doubt find a place on the wall at some future point.
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