BMW Releases Details on "Big Boxer" R18 Engine

Dennis Chung
by Dennis Chung

We were expecting BMW to debut its new “Big Boxer” cruisers at EICMA but were left disappointed with yet another concept model. We don’t have anything against concepts, really, but the R18/2 shown at EICMA was already the fourth to incorporate the new engine, and despite the spy photos that have popped up, it seems like BMW’s new cruisers just aren’t quite ready for full production yet.

We may be getting closer to that point now, as BMW has finally released technical details on the new R18 Big Boxer engine. We already knew the engine was an air and oil-cooled flat Twin with overhead valves manipulated by pushrods. We now know that the engine has a displacement of 1802cc from a 107mm bore and 100mm stroke, and a compression ratio of 9.6:1.

According to BMW, the engine produces 89.8 hp at 4750 rpm and more importantly for the heavyweight cruisers it’ll power, 116.5 lb-ft. at 3000 rpm, with 110 lb-ft available at just 2000 rpm. The engine speed tops out at 5750 rpm and idles at just 950 rpm. The engine itself weighs a claimed 244 pounds, and that includes the six-speed transmission and intake.

Like the BMWs of yore, the engine is air and oil cooled and uses an OHV configuration. The classic look is paired with modern technology, with four valves per cylinder, dual ignition, intake manifold injection and an engine control unit to manage all that torque while also helping the engine meet Euro 5 emission standards. Like the R 51/2 engine produced in 1950 and 1951, the engine uses two camshafts, positioning them above the crankshaft. This allows for shorter pushrods which reduces moving masses, allowing for improved control precision and stability at higher engine speeds.

The two intake and exhaust valves move in pairs via fork toggle levers. The intake valves are 41.2mm in diameter and are positioned at a 21 degree angle while the exhaust valves are 35mm and angled at 24 degrees. Valve clearance adjustments can be made by manipulating an adjusting screw for each valve.

The engine will use a single-disc dry clutch with a anti-hopping design to mitigate back torque under hard downshifting. The constant mesh six-speed transmission employs four shafts with helical gear pears. The gear input shaft rotates the two gearbox shafts while an output shaft reverses the rotation for the rear wheel. We still haven’t seen the bike this engine will go into, but BMW is already announcing an optional add-on reverse gear which is driven by an intermediate gear and an electric motor.

As illustrated in the R18 Concept, the drive shaft is nickel plated and exposed to spin in the open air, as was common in BMW boxers before 1955.

We expect the Big Boxer engine will be employed in a range of new models, including a classically-styled cruiser, a tourer, a bagger, and likely a more modern-looking performance cruiser similar to the R18/2 Concept shown at EICMA.

BMW R 18 “Big Boxer” Technical Specifications

Engine TypeAir/oil-cooled 2-cylinder boxer engine
Bore x Stroke107mm x 100mm
Compression Ratio9.6:1
Output89.8 hp at 4750 rpm (claimed)
Torque116.5 lb-ft. at 3000 rpm (claimed)
FuelPremium unleaded 95-98 RON
Valve controlOHV
Valves per cylinder4
Ø intake/outlet41.2 mm/35.0 mm
Ø throttle valve48mm
Engine controlBMS-O
Emission controlClosed-loop three-way catalytic converter, exhaust standard EU-5
Dennis Chung
Dennis Chung

Dennis has been a part of the team since 2008, and through his tenure, has developed a firm grasp of industry trends, and a solid sense of what's to come. A bloodhound when it comes to tracking information on new motorcycles, if there's a new model on the horizon, you'll probably hear about it from him first.

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  • Bubba Blue Bubba Blue on Dec 05, 2019

    It's all right. It is a little large looking, sticking out. I think I would prefer the Moto Guzzi arrangement for looks, but I don't know how these things fit.

    I know I like belt drive, which a BMW isn't going to have.

  • Eric Eric on Dec 07, 2019

    Great marketing idea: Chase an aging, waning, dying market to make stuff worse than those who've built the market and are quickly scrambling to the bail buckets.