The most powerful BMW boxer engine has its historical roots in full torque

After showcasing the R18 cruiser and the R18/2 performance cruiser at the recently concluded EICMA show, the Bavarian chaps have unveiled more details of the beautiful new Boxer engine, christened the “Big Boxer.”

Running point on the classic future of BMW – the R 18s’, this Boxer Engine replaces the 1,649cc in-line 6 of the K 1600 series to become the biggest displacement engine from the German guys. And doing so, it also becomes the largest twin-cylinder engine by BMW, and also the biggest flat-twin ever produced. Here are some of the specs revealed to us:

BMW's new “Big boxer” engine unboxed Exterior
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Type Horizontally Opposed Twin
Displacement 1802cc
Bore x Stroke 107mm x 100mm
Maximum power 91 hp @ 4750 rpm
Maximum torque 116 ft/lbs @ 3000 rpm
Compression ratio 9.6:1
Transmission 6-speed Constant mesh
Maximum rpm 5,750 rpm
Valvetrain Dual cams w/ pushrod-actuated valves; 4 vpc
Cooling Air and Oil cooled
Fuelling 48mm throttle bodies
Emissions Closed-loop three-way catalytic converter; Euro 5 compliant
Weight 244 pounds

DESIGN

BMW's new “Big boxer” engine unboxed Exterior
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Designed to be synonymous with the BMW Motorrad productions of the 1920s’, this air/oil-cooled mill gets a clear intent of optimal reliability, ease of maintenance, and powerful technology. This also features separate housing for the engine and transmission that distinguished the very first boxer engine, which at that time had laterally controlled valves.

Even after having four valves, dual ignition, a modern combustion chamber architecture, intake manifold injection, and the BMS-O engine management system, BMW has purposefully intended to make use of the classical Over Head Valve (OHV) configuration for its valve drive. This harks on the 2-cylinder boxer engine of the R 5/R 51 (1936 – 1941) and R 51/2 (1950 – 1951). A design BMW says that has been “highly valued by connoisseurs.”

They have even managed to make use of adjusting screws instead of hydraulic actuators to adjust valve clearances (0.2 – 0.3 mm), just like in the traditional BMW boxer role model.

PERFORMANCE

BMW's new “Big boxer” engine unboxed Exterior
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The maximum torque of 116 lb-ft is made available at just around 3000 rpm, while a good 110 lb-ft of torque comes from 2000 rpm through to 4000 rpm. This is said to provide for a thrilling pulling experience and in an exceptionally smooth manner, courtesy - a massive sized flywheel.

CONSTRUCTION

To minimize the vibrations even further, BMW has opted for an additional main bearing at the center to adapt to the enormous cylinder volume. Then there is the construction of the two camshafts on the left and right side above the crankshaft – this makes for reduced moving masses, minimized deflections, and lower linear expansions.

The crankshaft has been forged from quenched and tempered steel, and so are the two connecting rods with I-shaft. The pistons, however, are aluminum casts, and the valves are made of steel. The running surface of the light metal cylinders is coated with NiCaSil for smoother operation.

LUBRICATION

BMW's new “Big boxer” engine unboxed Exterior
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Lubricating and cooling oil is supplied by a wet sump lubrication system with a two-stage oil pump via a sleeve-type chain driven by the crankshaft.

TRANSMISSION

This Big Boxer embodies the same single-disc dry clutch transmission, but now, for the first time, comes with a self-reinforcing anti-hopping clutch to prevent unwanted rear wheel stamping during those aggressive downshifts. A propeller-shaft transmits the torque from the gearbox to the rear wheel.

The 6-speed device can also be optimized to use a reverse gear that is available as an optional extra. It can be driven by an intermediate gear and an electric motor and can be shifted manually.

BMW's new “Big boxer” engine unboxed Exterior
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Sagar Patil
Motorcycle industry expert since 1997! - sagar@topspeed.com
Over the years, a deeper conscience of machines moving body and soul has given him a crisp grasp over the concepts of motorcycling. A sucker for details and common sense, he loves getting his hands dirty every once in a while. His love affair with motorcycles ushers in the specialist skillset making Sagar our go-to expert for everything on two-wheels.  Read More
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