BMW has been famous for their robust, smooth and easy to maintain and access twin cylinder boxer engines. Boxer engines are basically a V engine with 180 degree angle for the V. The most famous BMW motorcycles have always been powered by the Boxer engines for the last 70 years staring with the R5/ R 51 built from 1936 to 1941 and then the R 51/2 built from 1950 to 51.
The latest iteration of the Boxer has been seen on the Concept R 18 and Concept R18/2 bikes which were showcased recently. True to their heritage, these bikes are powered by the largest boxer engines, using several design cues from the engines produced over the last 70 years by BMW Motorrad. These engines displace 1,802 cc with an over square engine with a bore of 107. 1 mm and stroke of 100 mm. This engine produces 91 HP of power at 4,750 rpm and 158 N-m of torque at 3,000 rpm. For a smooth and effortless drive, the engine produces 150 N-m of torque over a wide band from 2,000 to 4,000 rpm. The red line for this engine is 5m750 rpm while it idles at a leisurely 950 rpm.
Though these engines breathe through four valves per cylinder, they are operated using the 70 year old Overhead Valve (OHV) technology with pushrods to operate the valves. However, unlike other OHV designs by BMW Motorrad, this engine has two camshafts driven by the crankshaft via a sleeve-type chain. This helps reduce the size of the pushrods. Notwithstanding, the engine has all the modern trappings like 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. 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. Also, valve clearance compensation is not effected by means of hydraulic elements, but via one adjusting screw with one lock nut for each valve, as was always the case with these engines for the last 70 years.
All the power and torque is transmitted to the rear driving wheel through a dryplate clutch and a six speed constant mesh transmission. As was the case with all big BMWs, the power and torque is transmitted through a propeller shaft and not chain.