Harley Davidson recently announced its 2020 lineup, and it looks like nothing groundbreaking is coming in the coming year as Harley’s new liquid-cooled DOHC engine is not yet ready for production.
New Harley Davidson engine design
However, while we wait for a new platform from the American manufacturer, development of traditional engines continues. As it turns out, a design patent application was filed for the heir to Milwaukee-Eight in February, and was recently published by the US Patent and Trademark Office. According to the filing information, Harley Davidson is working on a new overhead valve system for the V-twin that provides higher crankshaft speeds than the current Milwaukee-Eight.
The most obvious change is that there are now two rods on opposite sides of the cylinder, as opposed to modern engines that have them side by side on the same side of the cylinder. Current engines use rods to drive twin rocker arms, one of which opens two intake valves and the other opens two exhaust valves.
The new engine still has four valves per cylinder, but instead of twin rocker arms, each rod drives a single one. When the rod moves up, the rocker pushes the intermediate tappet, which drives the two valves at the same time.
The problem with intermediate tappets is that they need to maintain a precise position in order to push the valves. The Harley patent is designed to prevent tappet positioning from being altered. According to the patent, the pusher moves along a stationary axis, and a special guide pin (item # 230 in the figure) holds it while preventing it from turning. As a result, the valves are able to open and close synchronously even at high engine speeds.
According to the patent, known intermediate tappet timing systems are capable of reaching a maximum rotational speed of 4000 rpm, but Harley Davidson claims the new design achieves a maximum rotational speed of between 6800 and 7000 rpm. At the same time, the current Milwaukee-Eight has a cut-off in the region of 5500 rpm. The patent also states that the intermediate tappets will be easy to replace during maintenance by lifting the rocker arms and unscrewing the guide pin.
Apart from the timing system, the patent contains almost no details about the new engine, other than information that it is a V-twin.
The patent includes an image of Softail, but it appears to be included there just for example, as the image shows the booms positioned on one side and is inconsistent with the rest of the drawings in the patent. This image, plus four valves per cylinder, suggests that the new engine will replace the Milwaukee-Eight, however, nothing will prevent Harley Davidson from using this design in the future Sportster.
In any case, the patent tells us that Harley is not ready to abandon the bottom design, even as it prepares for liquid-cooled overhead engines.