BMW's R 18 'Big Boxer': 91hp/158Nm

BMW has given more detail on the newly developed 2-cylinder ‘Big Boxer’ engine that is set to power its future R 18 cruiser.

The ‘Big Boxer’ harks back to traditional boxer engines in terms of its outward appearance and its technical specifications and with 1802cc, it will be the highest capacity boxer engine used in motorcycle series production.

The engine’s output is 91hp (67kW) at 4750 rpm. The maximum torque of 158Nm is already available at 3000 rpm. More than 150Nm is now available from 2000-4000rpm. This will hopefully ensure enormous pulling power and – in conjunction with a generously sized flywheel mass – exemplary running smoothness as well. The maximum engine speed is 5750rpm, while the idling speed is 950rpm.

The new ‘Big Boxer’ is air/oil cooled, has large ribbed cylinders and cylinder heads, and weighs 110kg including the gearbox and intake system. It has a vertically split aluminium engine housing.

Unlike the classic boxer engines, the new boxer crankshaft has an additional main bearing at the centre, which was necessary due to the enormous cylinder volume in order to precent 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.

The new boxer has four valves, dual ignition, a modern combustion chamber architecture, intake manifold injection and the BMS-O engine management system, but it uses the classic OHV configuration for its valve drive.

BMW engineers were inspired by the boxer engine of the R 5/R 51 (1936 – 1941) and the R 51/2 (1950-1951), and as in that role model, the two camshafts are positioned to the left and right above the crankshaft in the new boxer.

Like the traditional boxer, the new engine features a fork rocker arm and manually adjustable valve clearance compensation via adjusting screws.

It will also include constant mesh 6-speed transmission and self-reinforcing single-plate dry clutch with anti-hopping function.

As in all BMW motorcycles with boxer engine, 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.