The first Harley-Davidson V-Twin engine was released in 1909 in the form of the Atmospheric V-Twin.
Since that time the Motor Company has sold a total eight V-Twin engine designs – Atmospheric V-Twin, F-Head, Flathead, Knucklehead, Panhead, Shovelhead, Evolution, and Twin Cam – most of these names are instantly recognizable to almost any motorcyclist. So, when considering the relative rarity of Harley engine redesigns and the importance of the engine to one of the world’s biggest motorcycle manufacturers, you can bet that any major changes are well thought out and refined to a degree that lesser OEMs might have a tough time matching. With all that’s literally riding on a new engine, Harley’s project planners turned to the tools that have worked the best in recent years.
Harley’s Project Rushmore, unveiled only three model years ago in 2014, turned to members of the riding public to quantify what they wanted in a touring motorcycle. For the 2017 touring models, Harley’s researchers and engineers again picked the brains of both current Harley touring bike owners and riders who are interested in the marque but haven’t yet pulled the trigger. The result is the new Milwaukee-Eight engine. With interviews conducted in seven cities around the world, 1,000 riders were asked to outline what they would like to see in the next generation of H-D touring bikes.
Over time, several common themes became clear to the designers. First – and this should come as no surprise to any motorcyclist – these riders wanted more power from the 45° V-Twin. These requests were further broken down into two major groups: those who wanted more roll-on power and those who wanted the hot-rod feeling of power building all the way to the rev limit.
Second, riders wanted more comfort. Engine heat plays a dramatic role in rider comfort both out on the highway and when cruising around town, and riders made it clear that they wanted less heat flowing up from the rear cylinder and exhaust system – not just for themselves, but their passengers, too. Also, some riders – in this case, frequently potential Harley owners – wanted reduced vibration.
One area that lanky Americans and Central Europeans may forget is that the rest of the world is significantly shorter in the inseam. So, these focus groups pointed out that they would like for the touring models to fit their shorter statures better. Finally, and most importantly, the updated models needed to have the look, sound, and feel of a Harley-Davidson. The consensus among the interviewees was summed up by Alex Bozmoski, Chief Engineer of the Milwaukee-Eight Project, as “I want it to look like a Harley-Davidson from a football field away, but I want it to look like a new Harley-Davidson from 25 feet.”
The most obvious change in the powerplant is right there in each engine’s model name: Milwaukee-Eight 107 and Milwaukee-Eight 114. The Twin Cam 103 engine grew to 107 cu. in. thanks to its new bore and stroke of 3.937 in. x 4.375 in. (99.999mm x 111.125mm) while the 110 jumped up to 114 cu. in. via its 4.0-in. x 4.5-in. (101.6mm x 114.3mm) bore and stroke. However, the changes go much deeper than having bigger lungs to fill. The four-valve head is said to flow 50% more than the Twin Cam’s – a good thing since the Screamin’ Eagle big-bore kits can bump the displacement to 114 cu. in. and 117 cu. in. respectively, and that’s before we even consider the home-grown hop-ups that many H-D engines receive.
Still, this ground-up revision of Harley’s venerable V-Twin is more than just mounting a pair of bigger jugs.The four-valve head brought its own design considerations into play. The entire valve actuation system changed. Some readers may not remember that prior to the Twin Cam engine, the Evolution series utilized a single cam. With the Twin Cam the change was required to help reduce the angles on the pushrods to allow for higher valve lifts and more aggressive tuning, and these challenges couldn’t be solved without switching to dual cams. However, current modeling technology has allowed for the single cam to return, bringing with it multiple advantages: less parasitic power losses, less complexity, and less mechanical noise (one of the engine’s primary design goals). The switch to a four-valve head also had other benefits. Smaller valves have lower mass, requiring less spring to close, which results in a lessened impact on the valve seat. This reduced the beating the valve seats take and translates into lessened valve wear and lower noise.
Another interesting feature of the new heads is the lack of left-to-right valve lash adjustment on the pairs of intake and exhaust poppets. Today’s tighter manufacturing tolerances allow for the variance in the gap between the fingers and the valve stems they actuate to be reduced to a mere 0.003 in. It takes a variance of 0.010 in. to be able to hear the valve noise and see accelerated wear. With that difference reduced, the engineers determined that no lash adjusters needed to be installed.
Read the full article: Motorcycle.com