A new Harley-Davidson engine doesn’t come along very often so the launch of the Milwaukee-Eight is a landmark event.
Powering some of the firm’s 2017 models, the new engine is eventually likely to filter into all the firm’s large-capacity machines, replacing the Twin-Cam.
Unlike that engine, which has two camshafts to operate two valves per cylinder, the Miwaukee-Eight has just one camshaft but eight valves. Four-valve heads combined with pushrods is a pretty unusual arrangement, but it’s vital to the new engine’s improved performance and better emissions.
In fact there are three versions of the Milwaukee-Eight. The first is an air-cooled ‘107CID’ (1745cc) motor. It will appear in the 2017 Street Glide Special, Road Glide Special, Road King and Freewheeler models.
Next comes the ‘Twin-Cooled’ version of the 107. Like existing Harleys using the ‘Twin-Cooled’ name, it gets water cooling passages in the cylinder heads. It will feature in the Ultra Limited, Road Glide Ultra and Tri Glide Ultra.
Finally there’s a Twin-Cooled 114CID version, with an 1870cc capacity and more power. It’s set to be used in the CVO Limited and CVO Street Glide.
While Harley hasn’t released any figures, it says the Milwaukee-Eight engine produces ‘up to 11% more torque’ than the older engines.
Alex Bozmoski, Harley-Davidson Chief Powertrain Engineer, said: “The Milwaukee-Eight engine retains the classic Harley-Davidson 45-degree V-Twin design. It also retains the power characteristic that is the real legacy of the Harley-Davidson Big Twin: strong low-end torque with a broad, flat power curve through the mid-range that’s ideal for the Touring motorcycle rider.”
The torque increase translates directly to improved performance, with Harley claiming bikes with the 107 version accelerate 11% faster than their forebears with the High Output Twin Cam 103. The Milwaukee-Eight 114 gives 8% better acceleration than the Twin Cam 110.
There are also claims that the new engine, which has two spark plugs per cylinder, has up to 7% better economy. Cooling is also improved, largely because the new motor uses flat-topped pistons and shallow combustion chambers. The older engines’ domed pistons and hemi heads gave more area for combustion heat to soak into the heads and pistons.
Being a Harley, the engines’ appearance is also vital.
Brad Richards, Harley-Davidson Director of Styling, said: “The Milwaukee-Eight engine is styled to project power. I compare it to the back of a swimmer, lean in the waist but broad and muscular in the shoulders.”
“The rocker covers look like skin stretched taut over muscle, like the rocker arms are about to burst out of the engine. For the first time since the Knucklehead, the rocker covers reflect the action going on below. And they are massive. When you sit on the bike you can look down and see more of this engine.”