Harley-Davidson is set to unleash its 2017 model range in late August with one of the biggest shake-ups in the motor company’s history – it’s set to introduce a completely new big-capacity V-twin 1753cc (107 cubic inch) engine intended for Harley’s top-of-the-range motorcycles.
Information on the engine is still sketchy and largely confined to internet rumors, but it’s believed to be the recipient of the ‘Milwaukee-Eight’ name Harley trademarked two years ago with the ‘Eight’ referring to the number of valves.
While a Harley-Davidson with a four-valve-per-cylinder head design isn’t as radical an idea as it once was – after-all, the Harley-Davidson V-Rod has used eight valves for years – the Milwaukee-Eight design is far from conventional. In keeping with Harley-Davidson roots, the new engine doesn’t go in for those new-fangled overhead camshafts, instead sticking with the pushrods and rockers that are so intrinsically linked to the traditional cruiser scene. Of course, operating eight valves via pushrods is a little more complex, and to achieve it Harley-Davidson is believed to have switched from two camshafts (one for each cylinder) to a three-camshaft design. This layout is similar to the one already used on Indian’s big V-twins, but the Harley-Davidson’s cylinder heads will be more complex to allow four valves to be fitted.
Pushrods and four-valve heads aren’t a common combination. That’s largely because engines with lots of small valves are usually designed to rev high, and as such are developed with peak power in mind rather than low-end torque. Pushrods lead to a heavy valve train that goes against this high-rev thinking.