BMW Motorrad’s R 18 “Big Boxer”

More throttle!
The most powerful BMW boxer engine of all time with historical roots and full torque.
We love it when a plan comes together. Clearly the heart of this monster is beating fiercely already! (see video)

“Motorcycling in its most authentic form: instinct over mind, technology not for its own sake but as a way of creating space for fantasy and powerful emotion rather than sober contemplation and objective calculation.”
This was the message that accompanied the debut of the BMW Motorrad Concept R 18 at the Concorso d’Eleganza Villa d’Este in May 2019 – a striking revival of the BMW Motorrad brand core, namely the boxer engine.

It’s alive!
More than any other present-day BMW motorcycles before it, the Concept R 18 translated the essence of famous BMW Motorrad classics into the modern era, in particular in terms of form, while at the same time providing a glimpse ahead to a volume-production motorcycle that would enrich the BMW Motorrad Heritage world of experience in the near future: the BMW R 18.
The highest-capacity 2-cylinder boxer engine of all time. Yes! We want it!

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 Custom Works ZON and “Birdcage” by Revival Cycles. BMW Motorrad now presents this new, highly distinctive engine in detail.

It’s got the looks AND the performance
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 and oil cooled
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.

History repeated
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.

Shaft it!
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.

Technical specifications – BMW R 18 “Big Boxer”.
Engine
Big Boxer engine
Capacity
1802cc
Bore/stroke
107/100 mm
Output
67/91kW/hp
at engine speed
4,750 rpm
Torque
158Nm
at engine speed
3,000rpm
Type
Air/oil-cooled 2-cylinder boxer engine
Compression
9.6:1,
Fuel
Premium unleaded 95-98 RON
Valve control
OHV
Valves per cylinder
4
Ø intake/outlet
41.2/35.0 mm
Ø throttle valve
48 mm
Engine control
BMS-O
Emission control
Closed-loop three-way catalytic converter, exhaust standard EU-5