Inside Harley’s New Milwaukee-Eight

Andy H Harley-Davidson, Tech Leave a Comment

In the biggest roll-out of technology since Project Rushmore, The Motor Company’s 2017 tourers will have an all-new heart, and in classic Harley-Davidson style it is very much an evolution.

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With its single camshaft – chain-driven off the crankshaft – it will be seen by many as more an evolution of the Evo, and few details of the internal engineering are available at the moment, but the nose cone and the close-fitting lifter blocks of Harley’s newest 45° v-twin will be familiar to traditional fans.

Harley famously switched to a Twin Cam design in 1999 to get better valves angles for the cylinder heads they wanted to use, but with a change to 4-valve heads, that’s changed again: partly to reduce the weight of components in the valve train and their complexity as well as reducing friction and noise, but also because it can run leaner with higher compression ratios.

Basically, two smaller valves can flow better than big one, providing that you can operate them efficiently – always a headache on a hemi, getting the rocker angles right – but by using a pent roof combustion chamber they have made life easier on themselves, and have given themselves an opportunity to fit a second spark plug to get a quicker, cleaner burn. They have also fitted an electric decompressor to make life easier on a more powerful starter motor, and have managed – they say – to design a roller rocker that activates both valves in a pair that is set at the factory and is set-for-life. Each rocker is still activated conventionally by a pushrod with a hydraulic lifter between that and the cam to keep the valve-train quiet.

And with the single cam, the tighter V as defined by the pushrod tubes – barely visible on the stock engine with its dragstrip-inspired air-cleaner – has returned. So too have the tall pushrod tubes, running almost to the new split rocker boxes with echoes of the Panhead and Shovel, producing the most sculpted engine of Harley’s new age. Indeed, probably the best looking Harley-Davidson engine since the Shovel/Pan/Knuck*.

And Milwaukee-Eight?

Eight-valves.

If the intention was to create a new visual statement, it has succeeded in its goal, but Harley wanted – needed – more from it that that, and they’ve got that too:

  • More Power – the larger displacement, 4-valve heads and higher compression ratio produce up to 11% more torque
  • Quicker Acceleration – 2-3 bike lengths faster from 0-60 mph; 1-2 bike lengths faster from 60-80 mph in top gear
  • Improved Heat Management – heat absorption and increased heat dissipation, plus redesigned exhaust system has improved rider and passenger comfort
  • Improved Ergonomics – more accessible with a narrow primary and optimized air cleaner shape
  • Reduced Vibration – a new internal single counter-balancer working with isoplanar engine mounts provides a smoother, more refined feel at tickover
  • Richer Exhaust Note – a quieter powertrain distracts less from the iconic V-Twin rumble thanks to lighter valves, optimised cover designs and driveline improvements
  • Lower Tickover – a better sound and less heat
  • Improved Charging – 50% more output to power touring accessories.

The first brand new motor since the TC88B of 2000 – “every single part is new” – Harley describes it as being the most powerful, coolest running motors they’ve ever built: smoother, stronger and more durable.

It is currently available in Twin-Cooled 114 (1870cc) and 107-inch (1745cc) incarnations for ‘Ultra’ models with liquid-cooled exhaust ports and radiators in their fairing lowers, and a conventional 107 form with oil-cooled exhaust galleries for Road Kings, Road Glide Specials and Street Glide Specials and the Freewheeler Trike that we will be seeing here for the first time this year.

The power characteristic is said to be true to the legacy of Harley-Davidson’s big twins: “strong low-end torque with a broad flat power curve through the mid-range that’s ideal for the Touring motorcycle rider”, according to Alex Bozmoski, Harley-Davidson’s Chief Powertrain Engineer, and uses a long-stroke configuration of 100×111.3mm for the 107-inch motor, with the 114-inch CVO being both bored and stroked at 102×114.3mm.

It is going to be interesting to see how well these new motors lug, Harley having cajoled us into spinning the motor up more in recent times, but with a tickover down at 850rpm – and an oil pump that works at that speed – the suggestion is that it will a short-shifting torque monster. Indeed, it makes 10% more torque than the TC103, but we don’t know where, yet.

Traditionalists will be pleased to see a knife and fork big end running on roller bearings in the built-up crank, and everyone will be happier to see a single gear-drive balance shaft rather than the current chain driven arrangement, although perhaps surprised to see it on a rubber-mounted motor. All Milwaukee Eight motors will have a balance shaft and we know that the Touring models have a balance factor of 75% built in to lose some of the vibration at tickover but leave some sensation, and while Harley are tight lipped about the prospects of dialling in a higher percentage for a solid mount version of the motor, it is always a possibility.

While the six-speed transmission has been left unmolested, the primary drive has seen some work, with a new compensator sprocket outboard of a 24.5A alternator, and a slip and assist clutch, all housed in a slim-line primary case, similar to the one that was first seen on the Ultra Limited Low.

More as we know it.

(*delete as applicable)

#MilwaukeeEight #Harley2017 #Harley107

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