BMW Concept R 18 /2

BMW press release:

The BMW Motorrad Concept R 18 – a purist, historically inspired version of the big boxer – was presented by the BMW Group at the Concorso d’Eleganza in the Villa d’Este at Lake Como in the early summer. Six months later, at the world’s biggest motorcycle show – the EICMA in Milan – BMW Motorrad now presents its second sensational concept bike based on a big boxer engine: the BMW Motorrad Concept R 18 /2 (pronounced: “Slash Two”). It is the stylistic opposite of the Concept R 18: a modern, dynamic custom cruiser with a performance appeal that is somewhat rougher round the edges. As such, the BMW Motorrad Concept R 18 /2 demonstrates yet another potential expression of the Heritage concept, providing an impressive example of the flexibility and wide-ranging customisation options offered by this basic architecture.

“In contrast to the classic, elegant BMW Motorrad Concept R 18, the Concept R 18 /2 draws on its large boxer engine and frame to create a modern custom concept. The Concept R 18 /2 is uniquely extrovert. Elements from the past and future of BMW Motorrad merge here to create a captivating cruiser, making a powerful statement: “It’s a highly emotional bike designed for active riding. At the same time, the Concept R 18 /2 reflects the range of characterisations and customer dreams that we are able to realise using the same backbone,” explains Edgar Heinrich, Head of Design BMW Motorrad.

A performance cruiser à la BMW.

The BMW Motorrad Concept R 18 /2 celebrates the fascination of cruisers in an interpretation that is both sporty and modern. Minimalist handlebar trim together with the deep, elongated proportions promises a dynamic driving experience. The fairing, tear-drop fuel tank and seat form a flowing line that finds its perfect conclusion in the shortened rear wheel cover. All body parts are finished in Candy Apple Red metallic, an expressive red tone that highlights the flowing movement on the side. This luminous custom red with lots of depth is a real eye-catcher, changing from bright red to almost black depending on the incidence of light. Another striking feature is created by the graphic lines on the painted body parts, which extend from the side and top view of the fuel tank to the wheel cover and are visually prolonged across the seat. These give the Concept Bike a distinctive appeal.

The large boxer at the centre.

As in the Concept R 18, the centrepiece of the BMW Motorrad Concept R 18 /2 is a large 2-cylinder boxer engine with 1800 cc, including modern air/oil cooling and designed in a 1960s aesthetic. The engine is finished in a warm grey tone and has a sporty look, with an integrated breast cover, valve covers in a high-gloss black finish and a black frame. The engine badge bears the name of the Concept Bike, adding a high-quality accentuation.
After “Departed” by the Japanese customizer CUSTOM WORKS ZON, “The Revival Birdcage” by Revival Cycles in Austin, Texas and the BMW Motorrad Concept R 18, the BMW Motorrad Concept R 18 /2 is now the fourth interpretation of the large-volume BMW Motorrad boxer engine.

Attention to detail.
As a genuine BMW, the BMW Motorrad Concept R 18 /2 not only features a boxer engine, loop frame and tear-drop fuel tank, it also has a classic and elegantly showcased universal shaft. The striking cast iron wheels with 19” at the front and 16” at the rear create an equally discreet and dynamic dragster look, authentically rounding off the bike’s overall appearance. Meanwhile features such as high-performance Brembo brake calipers and Hattech stainless steel tailpipe system reflect the close attention to detail with which the BMW Motorrad Concept R 18 /2 was designed.
Multitude of possibilities.

The BMW Motorrad Concept R 18 /2 puts forward a new interpretation of a dynamic performance cruiser that not only taps into an area previously unexplored by BMW Motorrad but also demonstrates the true versatility of the “big boxer” platform. “After the BMW Motorrad Concept R 18, our aim with the Concept R 18 /2 is to demonstrate how flexible the basic engine and suspension are as a starting point for customisation, and how easy it is to authentically realise different styles. And I have to admit: we were very impressed at how it was possible to bring this boxer concept forward from the 30s via the 80s into the 2020s,” says Bart Janssen Groesbeek, BMW Motorrad Vehicle Designer for the Big Boxer Concepts.

Engine Overview

The highest-capacity 2-cylinder boxer engine of all time.
The heart of the new BMW R 18 is a completely newly developed 2-cylinder boxer engine – the “Big Boxer” – which has played a key role not just in the two BMW Motorrad prototypes – the Concept R 18 and the Concept R 18 /2 – but also in the custom bikes supported by BMW Motorrad, namely “The Departed” by ZON and “Birdcage” by Revival Cycles. BMW Motorrad now presents this new, highly distinctive engine in detail.

Not only in terms of its impressive outward appearance, but also from a technical point of view, the new “Big Boxer” ties in with the traditional boxer engines that were synonymous with motorcycles from Munich and Berlin-Spandau for around 70 years, from the beginning of BMW Motorrad production in 1923 through to the appearance of the air/oil-cooled successor: these were engines with a clear design, created for optimum reliability and ease of maintenance, featuring logically arranged yet powerful technology.

With its OHV valve drive along with a separate engine and transmission housing, the new “Big Boxer” has the same structural features that distinguished the very first BMW Motorrad boxer engine, which at that time had laterally controlled valves. The highest-capacity twin-cylinder boxer engine ever used in motorcycle series production is a 1 802 cc engine, resulting from a 107.1 mm bore and
100 mm stroke. The engine output is 67 kW (91 hp) at 4 750 rpm. The maximum torque of 158 Nm is already available at 3 000 rpm. More than 150 Nm is now available from 2 000 to 4 000 rpm. This ensures enormous pulling power and – in conjunction with a generously sized flywheel mass – exemplary running smoothness as well. These are the benefits of this level of performance and torque during riding. The maximum engine speed is 5 750 rpm, while the idling speed is 950 rpm.

Air/oil cooling, vertically split engine housing and triple plain bearing crankcase.
The new “Big Boxer” is air/oil cooled, has large ribbed cylinders and cylinder heads and weighs 110.8 kg including gearbox and intake system. It has a vertically split aluminium engine housing.

Unlike the classic air-cooled 2-valve boxer engines made by BMW Motorrad, however, the “Big Boxer” crankshaft, forged from quenched and tempered steel, has an additional main bearing at the centre, which was necessary due to the enormous cylinder volume in order to prevent undesirable bending vibrations of the crankshaft.

Like the crankshaft, the two connecting rods with I-shaft are mounted on plain bearings and are likewise forged from quenched and tempered steel. They accommodate cast aluminium pistons with two compression rings and an oil wiper ring. The running surface of the light metal cylinders is coated with NiCaSil.

Lubricating and cooling oil is supplied by a wet sump lubrication system with a two-stage oil pump via sleeve-type chain driven by the crankshaft.

Classic OHV valve drive with two camshafts as in the legendary R 5 to R 51/2 combined with modern 4-valve technology and dual ignition.
Although the new “Big Boxer” has four valves, dual ignition, a modern combustion chamber architecture, intake manifold injection and the BMS-O engine management system for the best possible torque as well as optimum consumption and emissions, it uses the classic OHV configuration for its valve drive – as was the practice pursued by BMW Motorrad over a period of some 70 years.

When developing the valve drive for the “Big Boxer”, BMW Motorrad engineers were inspired by a very special engine design in the history of BMW Motorrad – in keeping with the Heritage concept: the 2-cylinder boxer engine of the R 5/R 51 (1936 – 1941) and R 51/2 (1950 – 1951), the latter having been the first BMW motorcycle with a boxer engine after the Second World War. In contrast to other OHV designs by BMW Motorrad, this engine – highly valued by connoisseurs – has two camshafts driven by the crankshaft via a sleeve-type chain.

As in the historical role model, the two camshafts are also positioned to the left and right above the crankshaft in the “Big Boxer”. The advantage of this “twin camshaft boxer” is the shorter pushrods. This also makes for reduced moving masses, minimised deflections and lower linear expansions. A generally stiffer valve drive with improved control precision and higher speed stability is the consequence of this more elaborate construction.

Fork rocker arm and manually adjustable valve clearance compensation via adjusting screws as in the traditional BMW boxer role model.
In the traditional BMW Motorrad boxer design, the two pushrods actuate one pushrod per cylinder side for the intake and one for the exhaust side, guided in a sealed pushrod tube on the top of the cylinders. The two intake and exhaust valves in the cylinder head are actuated in pairs via fork toggle levers.

In contrast to today’s widespread engine technology, valve clearance compensation is not effected by means of hydraulic elements, but – as was the case in most classic air-cooled BMW two-valve boxers for decades – via one adjusting screw with one lock nut for each valve. As was formerly the case in the classic 2-valve boxers, valve clearance adjustment (0.2 – 0.3 mm) in the R18 “Big Boxer” is also achieved very quickly. The valves are made of steel, with a disc diameter of 41.2 mm on the inlet side and 35 mm on the outlet side. The valve angle is 21 degrees on the inlet side and 24 degrees on the outlet side.

Constant mesh 6-speed transmission and self-reinforcing single-plate dry clutch with anti-hopping function.
As in most BMW Motorrad boxer engines for decades (with the exception of vertical-flow, air/water-cooled boxers since 2012), a single-disc dry clutch transmits the torque generated by the engine to the transmission. For the first time it is designed as a self-reinforcing anti-hopping clutch, thereby eliminating unwanted stamping of the rear wheel caused by engine drag torque in the event of hard downshifting.

The constant mesh 6-speed transmission is located in a dual-section aluminium housing and is designed as a 4-shaft transmission with helical gear pairs. The gearbox input shaft with lug dampers drives the two gearbox shafts with the gear wheel pairs. An output shaft is provided to bridge the distance and reverse the direction of rotation. A reverse gear is available as an optional extra. This is driven by an intermediate gear and an electric motor and can be shifted manually.

Open secondary drive based on the classic role model.
As in all BMW motorcycles with boxer engines, torque is transmitted from the gearbox to the rear wheel in the R 18 via a propeller-shaft or universal-shaft drive with universal joint, shaft and rear-axle drive with bevel and ring gear. The propeller shaft and universal joint are examples of fascinating classic motorcycle technology since they are nickel-plated and open, as was commonly the case in BMW Motorrad models up to and including model year 1955. A so-called tripoid joint is applied on the gearbox side for the purpose of length compensation.