Harley-Davidson debuts Milwaukee-Eight engine

Posted3/26/2017 6:00 AM
  • A new Harley-Davidson Milwaukee-Eight engine shown on its Touring model.

    A new Harley-Davidson Milwaukee-Eight engine shown on its Touring model. Courtesy of Harley-Davidson

  • The Milwaukee-Eight engine has a more modern look to its air cleaner and rocker covers.

    The Milwaukee-Eight engine has a more modern look to its air cleaner and rocker covers. Courtesy of Harley-Davidson

Harley-Davidson made huge news last fall that had the motorcycle community just buzzing with the introduction of its new engine, the Milwaukee-Eight.

Historically, Harley makes improvements at a glacial pace. It isn't that its engineers aren't capable; they probably have the talent to make a flying motorcycle. It's just that they have to balance progress versus keeping the faithful happy.

Yet any company has to move forward with the technology necessary to attract new customers. And with ever more stringent fuel economy and noise regulations, the new Milwaukee-Eight engine meets those challenges.

The new M-8 is not an eight-cylinder engine, as the name might imply to those who drive only cars. It remains a 45-degree V-Twin, but with eight valves, hence the name. It's the ninth-generation big twin from Harley, following the Twin Cam 88 (which refers to 88 cubic inches) that was launched back in 1998. The Twin Cam 88 has grown to 103 and 110 cubic inches, depending upon the model of the motorcycle, and it still powers more than a dozen Harleys today.

For 2017, the M-8 is fitted on all the Touring and Trike models. It comes in two displacement sizes and three variations. For the Street Glide, Road Glide, Electra Glide Ultra Classic, Road King and Freewheeler, all models without fairing lowers, there is the 107 c.i. (1,750 cubic centimeters) version with oil-cooled cylinder heads. For bikes with fairing lowers, like the Ultra Limited, Road Glide Ultra, and Tri-glide Ultra, there's a 107 c.i. version with liquid-cooled cylinder heads. And there is also a 114 c.i. (1,870 c.c.) version with liquid-cooled cylinder heads for the top-of-the-line CVO Limited and Street Glide models.

Got that? Oil cooled and liquid cooled being the difference there.

I got to spend some quality seat time on the 2017 Road King, and this new engine is outstanding. I'm sure it will be developed further in the coming years to power other models in the Harley lineup. Before developing this new engine, the engineers had to work around certain parameters: it had to remain a 45-degree V-Twin, with pushrods and air-cooled fins; it had to have the right "potato-potato" exhaust note rumble; and it had to have the famous Harley torque when you twist the throttle. With all those boxes checked, they set out to have the new M-8 produce even more power and torque, vibrate less at idle, be narrower between the rider's legs, and keep the iconic look customers have come to love.

The Milwaukee-Eight is bored out to 100 millimeters vs. the Twin Cam 103's 98.4 m.m. and it retains the same 111.1 m.m. stroke to get those extra 4 cubic inches. Both old and new motors have the pushrod overhead valves with self-adjusting hydraulic lifters, but the M-8 doubles the valves per cylinder with four instead of two. That gives the new engine 50 percent more intake and exhaust flow.

The old engine has dual camshafts, while the new M-8 features a single, lighter, chain-driven cam that reduces friction and complexity -- and it's quieter. Compression ratio is bumped up to 10:1 rather than 9.7:1. Not a single part from the old motor is used on the new one. The new engine also sounds a bit cleaner.

According to Harley, the new 107 makes 111 foot-pounds of torque at 3,250 rpm (compared to 105 foot-pounds for the Twin Cam) and there's more torque across the entire rev range. They say the new bikes are 11 percent faster at zero-to-60 times, and top gear roll-ons are up 12 percent going from 60 to 80 mph. I have no reason to question those claims. And despite the increase in power, they've managed to improve fuel mileage, as well.

It also sounds cleaner and crisper. With all the extra demands from modern touring, there is 50 percent more power at idle from the electrical system, so you can crank up the heated clothing while using all the other kinds of amenities like GPS, phone, music, etc.

For those who are do-it-yourself mechanics, you won't have to adjust the valve train, regardless of how many miles you put on your bike.

To be honest, I've never enjoyed the "Harley Shuckle" vibrations at idle. But a new counterbalancer reduces those vibrations by a whopping 75 percent, and I'm on board with that move. You still get enough vibes to keep the character, but now it's not annoying and won't blur the mirrors.

The M-8 is still rubber mounted, so you get the same smooth operation once underway and all the way up to redline. The engine just feels more sophisticated and polished.

I rode the Road King on a warm day, which usually would have produced more engine heat than I like. But this new engine has gone to great lengths to alleviate much of the heat. Harley has improved airflow and combustion with more precise engine management, including antiknock sensors on each cylinder (which also aids in better fuel mileage), lower idle speed and dual spark plugs for each cylinder. It also relocated the catalytic converter and repositioned the rear exhaust pipe. The result is less heat reaching the riders legs and thighs, and that's really a welcomed improvement, especially for those slow rides down Main Street in Sturgis.

In addition, the modern-looking new air cleaner and rocker covers make the Milwaukee-Eight engine look as cool as it runs.

While the new Milwaukee-Eight is a major move forward for all the bikes it powers, it's by no means the only improvement. Check out my review of the 2017 Road King on Page 5 of this section for more upgrades to that model.

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