“M-8” top view showing tubular rockers
It happens every year and often it’s big news.
This year the launch of the Harley-Davidson 2017 motorcycle line-up is anchored by the new Milwaukee-Eight™107 and Milwaukee-Eight™114 power plants.
A couple weeks ago I posted about a new eight-valve Big Twin and now we know the rumors are true. The displacement of the standard version is 107ci (1,750cc) or in the CVO version it’s 114ci (1,870cc). The 2017 touring models get these engines first and may waterfall down to other models later in the year. The 107 uses precision oil-cooled cylinder heads and will be in the Street Glides, Road Glides, the Electra Glide Ultra Classic, and Freewheeler trikes. A Twin-Cooled version with liquid-cooled cylinder heads and radiators will be in the Ultra Limited models, the Road Glide Ultra, and Tri Glide models. The CVO Limited and CVO Street Glide models will have the Twin-Cooled Milwaukee-Eight 114.
M-8: Four-valve combustion chamber and the dual spark plugs
You might recall that the last major design evolution of the Twin Cam — and a significant part of the Project RUSHMORE and marketing campaign — was anchored on improving power plant cooling. This took the form of circulating liquid coolant in tubes around each cylinder head’s hot exhaust valve seat and then to external radiators. Many riders neglected to notice much in the way of decreased heat from this method of trying to get more power out of the 103.
So let’s talk details of the new eight-valve “M-8”.
M-8: Cutaway shows cooling areas of circulating liquid (Blue)
The 107 (3.937 x 4.375-inch bore and stroke) is cooled by pumping oil through it and then through a “chin radiator” ahead of the crankcase. In the 107 and 114 Twin-Cooled models (the 114 has 4.016 x 4.500-inch cylinder dimensions), water/antifreeze coolant is circulated through a cored heart-shaped passage that encircles the exhaust valves and then through radiators mounted forward to either side of the engine, as we’ve seen. The new engine uses a nearly flat chamber of minimum surface area with four valves and abandons the large surface area of the traditional deep, modified hemi two-valve combustion chamber found in the old design. The new engine operates at high compression ratios (as high as 10.5:1). As a result, the 2017 Touring motorcycles will provide 10 percent more torque. Harley states that will translate into two to three bike lengths faster from 0–60 mph, and one to two lengths quicker in top-gear 60–80-mph roll-ons along with improved fuel economy.
Overall airflow capacity of the “M-8” is 50 percent greater versus previous Big Twin engines, and the throttle body now has a 55mm bore. Each cylinder has an acceleration-type knock sensor along with ECM control which protects the engine from detonation. The new system is an improvement over the previous ion-sensing knock detection. The exhaust components, including the catalyst, have been relocated to help move engine heat away from rider and the new engines have a single four-lobe camshaft with automatic hydraulic tensioner in place of the Twin Cam’s pair which will help reduced mechanical noise.
And in a first for the rubber-mounted Big Twin is a single counter-rotating internal balancer. It’s meant to eliminate 75 percent of the engine’s primary shaking force. In addition, idle rpm has been cut from 1,000 to 850 rpm all in a effort to give riders improved engine smoothness. Other engine items of note is a new higher capacity alternator along with a new 1.6 kW (2.14 hp) starter that replaces the previous 1.2 kW (1.6 hp) units. There is a self-torque-boosting clutch with Brembo hydraulic actuation for a lighter lever pull and the engine ECM has been changed from a mapped system to torque-based which will be interpreted as a call for a specific torque level, not a specific throttle angle.
On the motorcycle side, the front and rear suspension is new. The new 49mm fork contains “dual bending valve fork technology” and uses cartridge-style variable-orifice damping valves, which Harley claims will deliver improved control at low speed without harshness over sharper bumps. This wasn’t achievable with the old system of fixed damping. Touring fork travel is 4.6 inches on standard models and 3.9 inches on low models.
After doing a quick H-D web site scan on the CVO Street Glide and CVO Limited models — it looks like the MSRP price went up $1K from 2016 ($36,799) to 2017 ($37,799). The same $1K increase is also shown for the CVO Limited ($39,999 to $40,999).
Only you can decide if the new 117 engine, the new suspension along with the radio power adjustment warrants the price increase.
Photos courtesy of H-D. Engine detail/stats courtesy of Cycle World.
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