Issue link: https://read.dmtmag.com/i/727617
36 nOctober 2016n www.thunderpress.net THUNDER PRESS by Kip Woodring Finally! An all-new Big Twin engine from Harley-Davidson! A bit late, but worth the wait! Since Harley doesn't do this every day (or every decade for that matter) this is a Big Deal Big Twin! For the purpose of this introduc- tory explanation of what it is and what to expect from it, I thought I'd simply interpret and expand on, as best I'm able, the information H-D has provided on this powerplant, point by point, and explore how The Motor Company goes about delivering on the slogan for the Milwaukee-Eight (M-8): "Stronger, cooler, with more comfort and style." Introducing brand new Big Twin engines and associated mechanical entities, like primary drives, clutches, transmissions and such, on the bread- and butter-bikes only, is a bold move by The Motor Company. Face it, Touring models are the backbone of Harley's model lineup, so to place this new engine exclusively in them— fi rst—is a gauntlet thrown in the face of those naysayers who blather on about never buying the fi rst year of anything. They say it's risky business until the bugs are worked out. Harley is betting the bugs have been extermi- nated in advance. It's a safe bet! The major engineering decisions that make this engine new (and vastly improved) amount to these: twin-plug four-valve heads, single camshaft, gear-driven counter balancer, and… wait for it… crankcase venting to the transmission. There's more, but mostly in detailed design, intended to enhance those main features. The fi rst 4-valve Harley heads since the board-track racers of the old days got those extra valves and those twin plugs because the power- plant has to be emissions compliant world-wide. It meets the toughest of those, "Euro 4," with no trouble. That's more than you could say for any previous Big Twin, but only tells half the story. What's best about the four-valve, twin-plug, pent-roof com- bustion chamber can be summed up in one word… potential. The level of effi ciency in this confi guration is such that the engine makes its power in a very low state of tune. Killing a lot of birds with this rock is easy. Lower emissions, improved power delivery everywhere in the rpm range, fuel economy, and lower operating temper- atures, to name a few. Those who want to turn up the heat (in both senses of the word) and use some of that latent potential are in luck! (We'll examine that subject in depth in next month's "Motorhead Memo.") The decision to use a single cam, regardless of how retro it appears on the surface, is actually the best way forward for this new four-valve, pushrod layout. Quieter because there are fewer parts thrashing around under the cam cover and because of gentler ramps, lobes and lifts… compared to camshafts that came before on Harley Big Twins. Because the fl ow in the heads is greater (by 50 percent, H-D says), massive amounts of lift are unnecessary. As is radical timing. Might take some adjustment in think- ing for folks who intend to hot-rod these engines but it amounts to less wear and tear on the entire valve train as well as better results from milder cams with "specs" worlds apart from the "traditional." Smoother V-twins are the rea- son for counter balancers in the fi rst place. The Twin Cam "B" got 'em in a chain-driven form to tame vibes in the solid-mount Softail chassis, but it was a piece of add-on engineering… and not without niggling faults. The Motor Company knew they could do better and now they have. This is a defi nite design improvement, if for no other reason than it cuts reciprocating weight, simplifi es and reduces parts count, is quieter and shall not fail or fl ail at high rpm (although for a Harley that's 5500–6000 rpm!). Then there's this: The Motor Company can obvi- ously, easily, change the balance factor to suit different applications. HARLEY-DAVIDSON MILWAUKEE-EIGHT 107 ENGINE The next-generation Big Twin The future's arrived—and it's bright Starting from the top—literally—there are stylish new two-piece rocker boxes… an easy way to visually recognize the new engine. Under them is where the action begins and there's a lot going on under the covers! Beefy, ribbed rocker arms for the four-valves, sitting in four pedestal mounts in each cyl- inder, catch the eye fi rst. Anyone familiar with Evo/Twin Cam arms will realize this design is both lighter and stronger, for quicker revs and durability at high revs. Operating smaller, lighter valves, against gentler cam ramps via beehive springs with lower pressures means greatly reduced loads, less friction, quieter operation and, more importantly, a lot more mileage between top-end overhauls. Yes, even though crankcase breathing is routed to a transmission sump cavity, some air and oil will manage to make it into the heads. So, there's this new one-piece breather valve located in each head. It's more effi cient than earlier designs and has a lot less to deal with in the fi rst place. Call it cheap insurance.