Munich. 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.
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.
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.
You will find press material on BMW motorcycles and BMW Motorrad
rider equipment in the BMW Group PressClub at www.press.bmwgroup.com.
In case of queries please contact:
Dominik Schaidnagel, Communications BMW Motorrad
Telephon: +49
89 382-50181, E-mail: Dominik.Schaidnagel@bmw.de
Tim Diehl-Thiele, Head of Communications BMW Motorrad
Telephon:
+49 89 382-57505, E-mail: Tim.Diehl-Thiele@bmw.de
Internet: www.press.bmw.de
E-mail: presse@bmw.de
The BMW Group
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