The Motor Company Unleashes A Brand New Engine
Harley-Davidson announced the release of its newest powerplant on August 23rd, 2016, and this should go down in history as the day Harley officially joined the 21st century. I mean sure, the Twin Cam motors were certainly an improvement over the aging Evolution Big Twins, which in turn was miles above the venerable Shovelhead and everything that came before, but this new plant is something else entirely.
Harley recently has developed a reputation for being receptive to customer input, as evidenced by the plethora of Project Rushmore features that the factory basically developed out of the suggestions/complaints box, and this newest creation is apparently an extension of that initiative. Introducing the Milwaukee-Eight, Harley’s ninth Big Twin built primarily from the wish lists of its touring clientele.
Continue reading for my look at the Milwaukee-Eight.
Heat, if you will forgive the pun, was a front-burner issue for the engineers. The old hemi-style combustion chamber was replaced by something a lot flatter, a move made possible by the namesake valvetrain that comes with four valves per head for a total of eight. Engineers claim a 50-percent improvement in flow rate over the old two-valve heads, allowing this engine to breathe more freely than ever before to the benefit of power production and emissions. This new shape is part of an effort to rid the engine of waste heat more efficiently by giving it less surface area through which to be absorbed. The flat combustion chamber and piston have roughly half the surface area of a hemi, so less thermal energy gets absorbed by the engine before it gets shunted off through the exhaust. Fear not, Oh ye of the old school; the factory didn’t do anything crazy like using over-head cams or any such foolishness, and it sticks to the traditional pushrod valvetrain with its massive rocker arms, just with an extra appendage to actuate the second valve.
Internal balancers counter much of the reciprocation mass within the engine, and according to the factory this mill only vibrates at about 25% of the intensity of the previous generation, so it will have just a taste of that Harley feel that some love, and others hate. These motors will all come with Harley’s slip-and-assist clutch, but conspicuous by its absence is any mention of traction control or variable rider modes, things that other premium brands are already well into production with, and in some cases into a second generation or more.
What the engine does come with is still pretty nifty. The factory took lessons learned from its Twin-Cooled Twin Cam engines and incorporated a similar technology into the new generation mill. The base Mil-8 107 (1,750 cc) uses oil jets for targeted cooling of critical areas, nothing really new there, but the Twin-Cooled Mil-8 107 and 114 (1,870 cc) circulates coolant around the exhaust valve to draw heat off from that hottest of spots. With all these features that defeat the heat, Harley was able to boost compression a bit for a claimed 10% more torque across the board. In short; more of everything we want, and less of the stuff (heat, vibration) we hate.
Expect to see these big V-Twins with their lumpy rocker-box covers in the touring models to include the Tri-Glide family and CVO bikes in the upcoming year, and if the usual pattern holds, in everything else as it phases out the Twin Cam plants.
Bear in mind that one of the main points of this engine is to meet new-for-2017 emissions requirements, so the transition may ultimately be more abrupt than the word “phase” suggests. We will certainly know for sure by this time next year, meanwhile I am eager to start riding bikes with this motor and gathering feedback from others, with a tiny part of me that wants to see what’s going to be the first thing to break on it. A mechanic’s morbid curiosity, nothing more.