The Boxer engine design was invented by German engineer Karl Benz in the 1890s. Yes, the man who helped establish BMW’s main competitor, Mercedes-Benz!
However, boxer engines weren’t used in motorcycles for a couple of decades and they were all placed with the cylinders in line.
BMW was the first to place the Boxer engine sideways in their R 32 motorcycle in 1923 with the heads sticking out the sides for more effective cooling.
It is called a Boxer engine because the pistons counterpunch like a boxer’s firsts.
The R 32 engine was designed by aircraft engineer Max Friz who used lightweight materials borrowed from aircraft manufacture, such as alloys in the pistons for the first time.
It also departed from other bikes of the time with no chain-drive between the engine and the gearbox and no chain or belt leading to the rear wheel. Instead, it had a sealed valve shaft which kept the bike and rider clean and was easier to maintain.
This model is based on the engine in the venerable R 90 S which was the inspiration for modern R nineT.
BMW R 90 S
It had a 49kW 898cc, four-stroke Boxer engine with large Dell’Orto carburettors and was capable of 200km/h.
The R 90 S was also the first series-produced motorcycle to come with a fairing fixed to the handlebars.
There have also been some spy shots, but not a full reveal which is expected early next year.
Even before a production model R 18 cruiser has rolled out of the Spandau factory gates, BMW Motorrad Australia is taking orders and deposits and has set up a dedicated site.
Big Boxer details
BMW says the Big Boxer engine will have overhead valves and a separate engine and transmission housing, but otherwise the same structural features of their first boxer which had laterally controlled valves.
It is BMW’s highest-capacity twin-cylinder boxer engine in motorcycle series production.
The Big Boxer weighs a hefty 110.8kg and has a 107.1mm bore and 100mm stroke.
Other features are large ribbed cylinders and heads with a vertically split aluminium engine housing.
Unlike their classic air-cooled two-valve boxer engines, the crankshaft is forged from quenched and tempered steel.
It has an additional main bearing at the centre, which is necessary 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 also 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.
Modern features include four valves, dual ignition, a modern combustion chamber architecture, intake manifold injection and the BMS-O engine management system for optimum torque and to meet Euro emissions targets.
However, it uses the classic OHV configuration for its valve drive of the legendary R 5 to R 51/2 from 70 years ago.
As in the historical role model, the two camshafts are positioned to the left and right above the crankshaft in the Big Boxer.
BMW says the advantage of this “twin camshaft boxer” is shorter pushrods which reduces moving masses, minimises deflections and lowers linear expansions for a stiffer valve drive with improved control precision and higher speed stability.
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 two-valve boxers, valve clearance adjustment (0.2 – 0.3 mm) in the R18 Big Boxer is also quick and easy. The valves are made of steel, with a disc diameter of 41.2mm on the inlet side and 35mm on the outlet side. The valve angle is 21 degrees on the inlet side and 24 degrees on the outlet side.
It is married to a constant-mesh six-speed transmission and self-reinforcing single-plate dry clutch with anti-hopping function to prevent rear-wheel lock-ups on rapid downshifts.
The transmission is located in a dual-section aluminium housing and is designed as a four-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.
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 classically nickel-plated and open, as used by BMW Motorrad in models up to 1955.
A so-called tripoid joint is applied on the gearbox side for length compensation.
Here is the official BMW Motorrad press release on the new models:
Further advanced boxer engine with BMW ShiftCam Technology for an additional increase in power across the entire engine speed range, reduced emission and fuel consumption levels, optimised running smoothness and refinement. With the extensively further advanced boxer engine, the new R 1250 R, R 1250 GS and R 1250 GS Adventure not only achieve a whole new level of power and torque. It was also possible to significantly optimise refinement and running smoothness – especially within the lower engine speed range. What is more, the new engine offers improved emission and fuel consumption levels as well as a particularly satisfying sound. For this purpose, BMW ShiftCam Technology has been used for the first time in the serial production of BMW Motorrad engines: this enables variation of the valve timings and valve stroke on the intake side. In addition, the intake camshafts are designed for asynchronous opening of the two intake valves, resulting in enhanced swirl of the fresh, incoming mixture and therefore more effective combustion. Other technical changes to the engine relate to the camshaft drive – now taken care of by a toothed chain (previously a roller chain) – an optimised oil supply, twin-jet injection valves and a new exhaust system.
Two riding modes, ASC and Hill Start Control as standard. There are two riding modes available as standard in order to be able to adapt the motorcycle to individual rider preferences. The standard Automatic Stability Control ASC ensures a high level of riding safety due to the best possible traction. The set-off assistant Hill Start Control is likewise a standard feature in all three models, enabling convenient set-off on slopes.
Riding Modes Pro, featuring additional riding modes, Dynamic Traction Control DTC, ABS Pro, Hill Start Control Pro and Dynamic Brake Assistant DBC, available as an optional equipment ex works. “Riding Modes Pro” is now available as an optional equipment item, featuring the additional riding mode “Dynamic” and “Dynamic Pro” (configurable), Dynamic Traction Control DTC, and in the R 1250 GS Adventure also the riding modes “Enduro” and “Enduro Pro” (configurable). DTC enables even more efficient and safe acceleration, especially when banking. ABS Pro offers even greater safety when braking, even in banking position. The new Dynamic Brake Control DBC provides additional safety when braking, also in difficult situations, by avoiding unintentional accelerator activation. By means of intervention in the engine control, drive torque is reduced during braking so as to make full use of the braking power at the rear wheel. This keeps the motorcycle stable and shortens the braking distance.
LED headlamp for the R 1250 RS and R 1250 GS Adventure as standard and LED daytime riding light for all three models as an ex works optional equipment item. The new R 1250 RS and R 1250 GS Adventure now feature a LED headlamp as standard. In addition to this, the LED daytime riding light is available as an optional equipment item for the R 1250 RS and the R 1250 GS Adventure as well as for the R 1250 R, which has halogen headlamps.
Electronic suspension Dynamic ESA “Next Generation” with fully automatic load compensation as an option. With the optional equipment item BMW Motorrad Dynamic ESA “Next Generation”, damping automatically adapts to the situation according to riding state and manoeuvres, and there is also automatic compensation in all load states. This allows finely tuned adaptation of the motorcycle to riding states, achieving optimum damping comfort and a very stable ride response.
Connectivity: Multifunctional instrument cluster with 6.5 inch full-colour TFT display offering many features as standard. The three new boxer models now have the equipment feature Connectivity as standard including a 6.5-inch full-colour TFT screen. In conjunction with the standard BMW Motorrad Multi-Controller, this means the rider can access vehicle and connectivity functions particularly swiftly and conveniently.
Intelligent Emergency Call as an ex works option. Ensuring the fastest possible assistance in the event of an accident or in situations of emergency and danger can save people’s lives. The optional equipment item Intelligent Emergency Call summons assistance to the scene as quickly as possible. As before, this feature can be ordered for all three models.
BMW Motorrad Spezial – high-quality customisation features as optional equipment items ex works. BMW Motorrad Spezial is range of iconic customisation features that enhance both performance and value, available as optional equipment items ex works. The focus is on harmonious integration in the vehicle as a whole, use of the very highest-quality materials, elaborate manual workmanship and characteristic attention to detail.
The billet packs Option 719 Classic and HP are available for the new boxer models, for example.
The new R 1250 R and R 1250 RS can also be equipped with the Option 719 Classic or Sport Wheels as well as the exclusive paintwork and the Option 719 seat.
An HP sports silencer is likewise available ex works for all three new boxer models.
New attractive colours and style variants. The new boxer models feature one basic finish each as well as two striking style variants. The Option 718 Special Paint Finish is also available for the new R 1250 R and R 1240 RS.
The highlights of the new BMW R 1250 R, BMW R 1250 RS and BMW R 1250 GS Adventure:
Further developed boxer engine with BMW ShiftCam Technology for variation of the valve timings and valve stroke on the intake side.
Even more power across the entire engine speed range, optimised fuel consumption and emission levels, increased running smoothness and refinement.
Increased output and torque: 100 kW (136 hp) at 7 750 rpm and 143 Nm at 6 250 rpm (previously:92 kW (125 hp) / 125 Nm at 6 750 rpm and 125 Nm at 6 500 rpm.
Capacity increased to 1 254 cc (previously: 1 170 cc).
Asynchronous valve opening on the intake side for optimised swirl and therefore more effective combustion.
Camshaft drive now via toothed chain (previously roller chain)
Optimised oil supply and piston base cooling.
Knock sensor system for optimised travel suitability.
Latest generation of BMS-O engine control and use of twin-jet injection valves for even more effective carburetion.
New exhaust system for optimum performance characteristics.
Two riding modes, ASC and Hill Start Control as standard.
Riding Modes Pro, featuring additional riding modes, Dynamic Traction Control DTC, ABS Pro, Hill Start Control Pro and Dynamic Brake Assistant DBC, available as an optional equipment item ex works.
Electronic suspension Dynamic ESA “Next Generation” with fully automatic load compensation.
Standard adjustability of the seat height on the R 1250 GS Adventure (exception Style HP) as well as a wide range of seat height variants ex works.
New optional Sports Handlebars for R 1250 R for a more dynamic riding position.
In addition to standard adjustability of seat height (exception: HP style for the R 1250 GS Adventure), wide range of seat height variants ex works.
LED headlamp for the R 1250 RS (completely new design) and R 1250 GS Adventure as standard; LED daytime riding light for all models as an ex works optional equipment item.
Connectivity: Multifunctional instrument cluster with 6.5 inch full-colour TFT display offering many features as standard.
Intelligent Emergency Call as an ex works option.
BMW Motorrad Spezial – customisation features as optional equipment items ex works.
Extended range of optional equipment items and original BMW Motorrad Accessories.
The new R 1250 R:
Dynamic naked bike character in one basic colour, two style variants and Option 719 Spezial finishes.
The new R 1250 RS: Sport and touring character in one basic colour, two style variants and Option 719 Spezial finishes.
New front spoiler and cockpit cover (R 1250 R and R 1250 RS).
Newly designed upper trim (R 1250 RS).
The new F 1250 GS Adventure: Off-road and adventure prowess in two modern basic finishes and two striking style variants.
R 1250 GS Adventure with new body features such as black-grained lid for storage compartment with embossed GS logo, trim for the intake snorkel, radiator trim with electroplated look, tank bracket and engine protection bars adapted to the design of the body frame.