The Secrets Of The New Harley-Davidson engine: Milwaukee Eight M8

As every year approaches the time (at the end of August) when Harley-Davidson presents the new models next year. Although so far everything is rumored, it seems that the new Milwaukee Eight engine, currently installed in Touring models, will equip the entire Big Twin range of 2018.

Let's review the technical details and features of this new M8 engine that the Motor Company launched 1 year ago and propels the range of Touring models 2017 and probably the other Big Twin models of the brand in the coming years.
Named Milwaukee-Eight in honor of one of its main novelties, the use of 8 valves in the cylinder heads, offers more torque and power than its predecessors without losing the "heritage" of its iconic image, keeping the angle at 45 degrees between the cylinders.

The new M8 is the ninth engine in the Big Twin saga:
Atmospheric-Twin (1909)
F-Head (1911)
Flathead(1929)
Knucklehead (1936)
Panhead (1948)
Shovelhead (1966)
Evolution (1984)
Twin-Cam (1999)
Milwaukee-Eight (2017)

Displacement and models
The Milwaukee-Eight is presented in 2017 in 3 versions:
107ci (1745cc) with oil cooled cylinder heads (Precission Cooling) for Street Glide Special, Road Glide Special, Road King/Road King Classic and Freewheeler models.
107ci (1745cc) with water-cooled cylinder heads (Twin-Cooled) for ultra Limited/Ultra Limited Low, Road Glide Ultra and Tri Glide Ultra models.
114ci (1870cc) with water-cooled cylinder heads (Twin-Cooled) for the exclusive Custom Vehicle Operations CVO Limited and CVO Street Glide models.

Twin-Cam on steroids?
Although at first glance the exterior looks quite similar to its predecessor the Twin-Cam, the fact is that this new propeller has been designed completely from the beginning, improving the strengths of previous models and correcting the shortcomings produced by the incessant increases in displacement and power of recent times. Let's review the main changes:

• More power: the M8 has 11% more torque, which, together with the larger displacement, provides a remarkably high power and performance.
• More acceleration: the M8 weighs the same as its predecessor and when this is added to its power boost you get an acceleration 11% higher than that of the Twin-Cam 103ci.
• Reduced fuel consumption: thanks to the use of double spark plugs per cylinder, optimized ignition and high flow cylinder heads with 4 valves per cylinder, engine efficiency is improved, reducing fuel consumption.
• Improved temperature management: the new design has managed to keep the heat inside the engine (which is where it should be) by reducing the temperature absorption of the cylinders and cylinder heads, helped by cooling (by oil or water) at the hottest points of the same.
• Improved pilot comfort: a new, thinner primary transmission cover and the lowered profile of the air filter cover improve rider legroom around the engine, facilitating ground access for many pilots. All models with the Milwaukee-Eight engine have an improved "assist and Slip" hydraulic clutch drive, which reduces lever effort by 7%.
• Pleasant vibrations: for the first time it has mounted a balancing shaft inside the engine attached to the chassis by silentblocks, which gives an unprecedented smoothness without losing "character".
• Enriched exhaust sound: many of the changes in the propeller have been aimed at minimizing the sounds inside the engine to be able to increase the exhaust sound while complying with the regulations regarding noise emissions. As it was said When The Evolution engine was introduced, "we reduce noise in order to increase music".
• Improved electric charge: modern motorcycles increasingly have more electrical and electronic devices (engine management, audio and multimedia, heating, lights...) so a new alternator has been installed that provides 50% more power with the engine idling, in order to meet these and future demands at the electrical level.
• Renewed exterior design: the engineers have wanted to respond to the aesthetic demands of the most loyal customers have given the M8 a "muscular" aspect, wrapping the mechanical parts in a more direct way, as if it were a mechanical skin, letting us intuit the components that are hidden under the covers. The surface of the cooling fins has also been increased, providing functionality and creating a more massive look.

Technology and tradition
The goal was not simple: to replace a well-functioning engine and meet the demands of modern customers in a globalized market, creating a refined product that meets expectations in terms of quality and brand heritage, all at a competitive price within the "premium" products. In order to achieve this and all of the above while increasing reliability and complying with the strictest standards for the different markets, the Harley-Davidson engineers have faced many mechanical design challenges that have been solved in a variety of ways, leveraging the experience of a brand over 100 years old and applying the latest manufacturing technologies.

Eight valves, four spark plugs... and a camshaft
With the addition of four valves per cylinder several objectives are achieved at the same time. This system makes it possible to create a flatter combustion chamber (with less surface area and therefore less heat absorbed), increasing the compression up to 10.5: 1 and the outflow and inflow of air by 50%. The valves are hydraulically actuated as in previous models and do not require any adjustment and allow the use of springs lighter than previous models.
Hydraulic pushers are driven by a single camshaft (as in Evolution and previous models) driven by a chain from the crankshaft and adjusted by a hydraulic tensioner. Choosing a single camshaft simplifies mechanics and reduces friction and unwanted sounds.
With double spark plug for each cylinder head we have improved and faster combustion, while increasing efficiency and consumption. Two sensors have also been installed (one on each cylinder head) that capture the vibrations of the engine for a better adjustment of the ignition, anticipating it as much as possible without reaching the "sting" or detonation. This system replaces the previous "Ion Sense", and has a higher resolution, working together with the programming of the switchboard so that the combustion is as complete as possible.
The cooling systems of the cylinder heads inherited from the Rushmore project are reused, providing internal passages to the points where more heat accumulates, and passing through them oil or water, depending on the model. Both the oil and water pumps have been redesigned to move a higher volume per minute, and idle speeds have now been lowered from 1000 rpm to 850 rpm.
As we have discussed above one way to prevent the engine from accumulating excessive temperature is to make the flue gases pass as quickly as possible outside. Together with the larger surface of the valves and the optimization of the ignition, the new design of the exhausts with the relocated catalyst facilitates this task in a more effective way, removing the heat radiated to the driver and passenger.

Strengthening the foundation
Obviously the increases in displacement and torque have to be accompanied by a low reinforced engine. The crankshaft shaft has been oversized and the bearings are able to withstand more load. The new crankcase is 23% stronger than the previous one, and still weighs the same. This has been made possible by the removal of unnecessary material, giving the appearance that the lids now "embrace" the inner parts, following their shape.
The new balancing counter axle consists of a mass that rotates in the opposite direction to the crankshaft and absorbs much of the vibrations emitted by it.
Another challenge in a large displacement engine with dry crankcase is the evacuation of pressure when the Pistons are lowered, for this need have been created new engine vents that more efficiently separate the air from the oil in suspension and connect with the crankcase transmission, preventing condensation in the air filter, as was often the case in previous engines.

Primary and transmission at Engine height
With the increase in cubicage, improvements in primary transmission are required. Converting the brutal torque generated by the pulses of 2 huge Pistons going up and down into a smooth and dosable rotary motion is no easy task, unless you use a huge crankshaft, subtracting efficiency. In this case it has been chosen to redesign the primary transmission, improving the ramps and clamping of the compensator and adopting a centrifugal force-assisted clutch, which is smooth with the engine a idling and gradually hardens as we accelerate, reducing the effort in the clutch lever (with Brembo hydraulic pump) by 7% without losing power. At the same time this device will prevent lockouts of the rear wheel in sudden decelerations (anti-lock clutch).
The starter motor is now more powerful, it has been changed from 1.2 kW to 1.6 kW and the solenoid has been modernized. The ECM helps during start-up by activating decompressors located on the cylinder heads and adjusting the ignition conveniently.
As for the transmission, one of the main innovations is also related to the elimination of internal noise, for which a system of "constant contact" in one of the gears has been used to eliminate gaps between them and improve synchronization.

SDBV suspensions
One of the most demanded points by potential users of Harley-Davidson touring models in markets outside the United States is the improvement in suspension, both in vehicle control and in ride comfort. The design team has introduced a completely new system that allows a preload adjustment of up to 30% higher than the previous ones in a quick and easy way.
The front suspension features a new "Showa dual bending valve" suspension technology with the cushioning performance of a competition cartridge fork, with a
more linear behavior and less weight. Basically this means that the fork adapts its hardness and operation in real time, "detecting" changes in the firmness of the terrain or in the speed of travel.

Screamin ' Eagle
As it could not be otherwise, HD's catalog of high-performance enhancement accessories (Screamin ' Eagle) already includes a multitude of components and kits to turn the M8 into an adrenaline generator. We can find from exhausts and air filters of higher performance homologated to” Stages " of potentiation that will transform the Milwaukee Eight, reaching up to the 117ci (1917cc).

Finding
When judging such a novelty, we must do so on the basis of the current circumstances and the evolving needs of the global market. Harley-Davidson needed to update its product after 17 years, under a very restrictive regulation that makes it very difficult to homologate a large-displacement engine with dry and air-cooled crankcase, all while maintaining the traditional aesthetics of the brand. New customers ask for modernity, power, softness and reliability, but with minimalism and "retro" tradition.
It seems that Harley-Davidson has risen to the occasion again, surprising with a blunt engine, which meets so many requirements with a shattering balance. For many more years.

Frank Burguera

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