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Harley Developing V-Twin With Variable Valve Timing

Seems there’s still some life left in the air-cooled pushrod engine.

By Ben Purvis, Cycle World with line drawings from the factory
8/3/2020


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Despite launching the LiveWire electric bike and entering a new performance echelon with the 145-hp, water-cooled Revolution Max engine, Harley-Davidson’s future is still firmly pinned on its traditional air-cooled, cam-in-block V-twins—and the firm is developing a completely new engine that ticks those familiar boxes.

New patent applications from the firm reveal that it’s developing a completely new air-cooled, pushrod V-twin that combines old-school appearances with modern technology including variable valve timing.


The new design would have a compact new balancer mounted to the crankshaft that would spin at the same speed.

Elements of the design are familiar Harley territory. It’s a twin cam engine, with a camshaft for each cylinder. Those camshafts are driven via an intermediate gear that drops their speed to half that of the crankshaft. It’s here that the variable valve timing is added.

The pushrod engine design actually makes VVT easy to implement. A single VVT actuator (or “variator”) is built into the intermediate gear, allowing the output side that meshes with the camshafts to be shifted by a few degrees in relation to the input side that meshes with the crankshaft gear. In comparison, a DOHC V-twin with variable inlet and exhaust valve timing would need four variators, one for each camshaft, and those would be mounted in the cylinder heads where they add undesirable bulk and weight.


 Cams are driven via an intermediate gear with a built-in VVT actuator or “variator.”
 
The position of the VVT system on the intermediate gear isn’t a new idea. Indian has also filed patents for an air-cooled V-twin with a similar layout, and Harley isn’t trying to get IP rights over the VVT element of the engine. Instead it’s hoping to patent a compact new balancer which is mounted concentrically to the crankshaft and driven by a chain and sprocket from the camshaft intermediate gear. The sprocket ratio doubles the balancer’s speed—so it spins at the same speed as the crankshaft—and the chain drive from the intermediate gear means it turns in the opposite direction to the crank, allowing it to offset crank vibrations.

A smaller, higher-revving engine such as the one found on the aging Sportster would likely benefit most from VVT.

Although this new engine sticks to Harley’s traditional 45-degree, air-cooled V-twin layout, its pushrods are a break from the norm. We’re used to seeing pushrod tubes running up the right-hand side of Harley V-twins, but on the new design there are pushrods on both sides of the engine. The front cylinder has its inlet valve pushrod on the left-hand side and exhaust pushrod on the right, while the rear cylinder’s inlet pushrod is on the right and exhaust is on the left. The heads are four-valve designs, with each pushrod operating a rocker that acts on two valves.


Pushrods on the new design now run up both sides of the engine and operate on four-valve heads, a switch from the usual Harley V-twin layout.

While many have suggested that future emissions laws, particularly in Europe, will make air-cooled, pushrod-valved engines a thing of the past, in fact that’s wide of the mark. The Euro emissions rules are actually much harder on high-revving engines. Big, lazy twins that don’t need high revs can achieve surprisingly clean emissions—the newly launched BMW R 18, for example, demonstrates that large-capacity, air-cooled engines will be with us for a long time to come.

Since Harley’s large-capacity Milwaukee-Eight is still a new design and created with future emissions rules in mind, there’s a good chance the new patents show a replacement for the age-old Sportster V-twin, which hasn’t changed substantially since the mid-1980s. As a smaller, higher-revving engine it’s more likely to benefit from VVT than the bigger V-twin, gaining both cleaner emissions and a boost in low-end torque.



Editor's Note: This is interesting. The factory wouldn’t comment on whether this engine is happening or not. Although, they blessed Bikernet to publish it. If you’ve been around, you remember when Harley engines were considered tractor engines and junk. They weren’t considered performance engines or capable of racing. Now, almost every manufacturer produces some semblance of a V-Twin. And according to this article, V-Twins are lower polluters than higher revving engines. Incredible. We rock! --Bandit

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