BMW R 1800 Big Boxer Twin Technical Details

BMW has been teasing its massive new 1,802cc Big Boxer engine for some time, showcasing the mill in customs from Zon and Revival Cycles, and within concepts like the R 18. Earlier this year we also got a glimpse at the production version of the bike to be powered by this unmistakable powerplant. That’s all to say that BMW’s made no secret of the new cruiser platform on the horizon, but details on the specifics of the engine have been sparse until now.

From the outside it’s clear that the design of the engine is rooted in BMW’s history, and so too are many of its technical features. It’s got separate engine and transmission housings and an OHV valve drive design similar to some of the earliest boxer engines produced by the brand. BMW looked specifically to the R 5/R 51 and R 51/2 for inspiration with the valve drive, mimicking the dual camshaft configuration in the Big Boxer. The latest engine has two camshafts positioned to the right and left above the crankshaft, allowing pushrods to be shorter and thereby reducing moving mass within the engine. This also serves to make the valve drive more stiff, allowing for better precision and stability.

The modern amenities of the four valve per cylinder system include dual ignition, intake manifold injection, and the BMS-O engine management system, all geared to provide peak torque and power while optimizing consumption and keeping emissions down.

When fuel is served up though the 41.2mm inlet valves, it fires within piston chambers that have 107.1mm bore and 100mm stroke, with spent gases exiting 35mm outlet valves. The cast aluminum pistons inside are driven by a tempered steel crankshaft that features an additional main bearing at the center to reduce bending vibration. They live within cylinders coated with Nikasil and are lubricated and cooled by a wet-sump lubrication system with two-stage oil pump that operates by way of a sleeve-type chain driven by the crankshaft.

Each of the steel valves is adjusted by an adjusting screw, similar to many of BMW’s classic air-cooled engines of the past, allowing valve clearances to be adjusted easily.

The aluminum engine housing is split vertically and utilizes air-cooling in addition to oil-cooling thanks to large ribbed cylinder housings. In total, the engine weighs 244.3 pounds.

As for output, there’s 91 hp available at 4,750 rpm and 116.6 pound-feet of torque at 3,000 rpm. Revs top out at 5,750 rpm and engine idle is set at 950 rpm.

All that power is transmitted to the rear wheel by way of a universal shaft drive and dry single-disc, anti-hopping clutch. The six-speed transmission is housed inside the second aluminum housing directly behind the primary engine housing. It utilizes a four-shaft design with helical gear pairs, with an input shaft with lug dampers driving two gearbox shafts and an output shaft that reverses the direction of rotation. Riders will also be able to add reverse gear functionality to the engine as an accessory, which is driven by an intermediate gear and electric motor.

BMW has achieved the largest two-cylinder boxer engine of all time with the Big Boxer, and the uniquely nostalgic/modern mill promises to be quite a treat for cruiser riders.