Harley-Davidson Revolution Max 1250 engine: A closer look

The Revolution Max 1250 engine. Photo: Harley-Davidson

Earlier this week, Harley-Davidson finally released the full details on its new Pan America 1250 adventure bike series. As a whole, the bike is big news; it has a much lower price than many of Harley’s more expensive machines, with latest-generation electronics and suspension.

But the new Revolution Max 1250 engine is almost as big a deal as the whole bike itself. This new liquid-cooled V-twin is going to be very important to Harley-Davidson in coming years, and it’s a big departure from the company’s previous stereotypes.

Power through tech

The Revolution Max 1250 is rated for 150 hp and 94 lb-ft of torque. This isn’t the most powerful engine H-D has ever made; the Destroyer drag bike made 165 hp, and was available over-the-counter. The VR1000 superbike was in this ballpark as well. However, those engines were race-only, and the new 1250 is a street engine. 

In the past, Harley-Davidson’s engines basically made their power through displacement. Every time the Big Twin series went to their next generation, they grew in size. The 88 became the 103 became the 107 and so on. Currently, you can buy a 131 ci Screamin’ Eagle drop-in replacement crate engine at great expense, and even that pricey upgrade makes around 120 hp, and would probably cost you close to half the price of a new Pan America by the time you got it installed. Maybe even more.

Variable valve timing is the key to Harley-Davidson’s new engine, but it’s designed for efficiency in every system. Photo: Harley-Davidson

The 1250 uses several tricks to make more horsepower, but the biggest factor here is the variable valve timing system (VVT). Harley-Davidson went with variable valve timing on both the the exhaust and intake cams. This allowed Harley-Davidson to make an oversquare, higher-revving engine but still retain its low-end torque.

The VVT system advances or retards exhaust and intake camshaft timing independently through a potential range of 40 degrees of crankshaft rotation, says Harley-Davidson’s press release. As a result, you’ve got a broader powerband, with better torque management and efficiency when compared to the same engine design with fixed valve timing. Efficiency helps the manufacturers meet emissions regs, and the entire industry is moving towards the whole broadened-powerband concept these days, even on non-VVT models. In other words, this is very much a modern engine, in line with what everyone else is doing. 

The engine uses all-aluminum heads (DOHC, four-valve) and cylinders, with Nikasil-lined cylinders for longevity (Suzuki and others have used this trick for years). Some of the engine’s covers and other bits were made of magnesium or other trick material. This saves weight, and helps the engine shed heat better. Harley-Davidson went with liquid cooling, of course, but note that the system is relatively compact. Not only does this help maintain the tidy look that Harley owners prefer for their V-twins, but it’s also important for a machine that could see rough use.

The oiling system is designed to reduce inefficiency. Oil feeds into the crankshaft itself, instead of the main bearings, which means the engine can run lower pressures and reduce drag. The dry sump design means rotating bits run above the engine’s oil reserve, so “parasitic power loss is reduced because internal engine components do not have to rotate through excess oil.” A set of three scavenging pumps draws excess oil from the crankcase, stator cavity and clutch cavity, reducing parasitic loss further. The oiling system also has jets aimed at the bottom of the aluminum pistons, to promote cooling, sort of like Suzuki’s old SACS system.

That theme of maximizing efficiency runs everywhere here. There’s dual-spark heads, and Harley-Davidson even used dual-strap sparkplugs, all to promote better fuel burn. There’s a dual down-draft throttle body setup, meaning each combustion chamber gets its own high-velocity airflow and fuel delivery, for optimized performance. This is all key to building a modern performance engine, especially one that meets emissions standard.

The Revolution Max has a slipper clutch and 6-speed gearbox. No auto-clutch tech, not even a quickshifter. That might be a good thing for the MoCo to consider; silly as it sounds on a Harley-Davidson, that’s where the market is headed. Photo: Harley-Davidson

Optimizing exhaust output is only one part of meeting modern emissions regs, though. The EU in particular is very worried about mechanical noise, and Harley-Davidson says the new engine’s liquid cooling allows for tight tolerances that reduce the traditional Harley clamour. Isn’t that what the stereotypical H-D owner wants? Well, the press release turns it around by saying  “Desirable engine sounds – a stirring exhaust tone – can predominate because noise from internal engine sources is reduced by liquid cooling.” Your new V-twin might not sound like your old V-twin, but Harley-Davidson says that’s a good thing. Indeed, you’ve got parts like the timing chain tensioner designed to minimize start-up noise clatter.

Harley-Davidson’s new engine has a 60-degree angle, with 30-degree offset connecting rod journals, working out to a 90-degree firing order. The counterbalancer design smooths out most engine vibration, although the engineers left a bit of feedback there, because that’s the Harley-Davidson formula.

There’s a 13:1 compression ratio; the engine is designed for high-test gasoline. An anti-knock system will let you run the 1250 on lower-octane gas, but it won’t be as efficient or powerful.

As usual with Harley-Davidson’s V-twins, the Revolution Max has hydraulic valve lash adjustments, which means you don’t have to fiddle with tappet clearance every few months. Oil change intervals come around the 5,000 mile mark (8,000 km, then), but oil changes themselves aren’t usually expensive or tricky, usually, especially for the DIYer. It shouldn’t be too expensive to keep this engine running in top shape.

The Revolution Max engine is also headed for Harley-Davidson’s cruisers. The Custom is the first concept bike we’ve seen from that line. Photo: Harley-Davidson

The next generation of Harley-Davidson

All things considered, the Revolution Max 1250 is a big step forward for Harley-Davidson, but if this engine only powered adventure bikes, it wouldn’t do the rest of the company much good. Harley-Davidson won’t be able to sell its cruisers overseas if those bikes don’t have proper modern engines, meeting current emissions standards.

That’s why it’s significant to note Harley-Davidson says it still plans to build the Custom cruiser around this engine. We’ve seen this cruiser before, a mean-looking muscle bike in concept form. If it gets the 1250 engine, it will be the most powerful cruiser in Harley-Davidson’s lineup by far, blowing the doors of any of the old street-legal V-Rod models. That’s just as important to the Harley-Davidson of the future as the Pan America.

 

5 COMMENTS

  1. The hydraulic valve lash adjustment feature is great. Motorcycle’s not circulating a racetrack and operating in the real world definitely from that. Good for Harley to have included this.

    • Agreed.
      That could be the difference maker for me if I were deciding which bike to buy, all other things being almost equal. For instance, adjusting the valves on either the Multistrada V-twin or V4 is not something I would want to do or pay to get done.

    • Same. I would trade my shaft drive for hydraulic valves. It takes a half hour to change a chain+sprockets. It takes a whole day to check and adjust a shim under bucket setup. Not to mention, it’s easier to mess it up.

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