ENGINE / DRIVE
SINGLE CYLINDER ENGINE 650 CC.
Lightweight, agile single cylinder motorcycles are generally regarded as the original form of two wheel transportation. They follow the principle of “less is more”.
In conjunction with the constant mesh five speed gearbox, this powerful and high rev single cylinder provides an equally fascinating response on twisting country roads as on forays into light terrain. In addition to its maximum of riding fun and refinement, yet another convincing feature of this agile engine is its exemplary low emissions.
The liquid cooled single-cylinder engine under the two overhead camshafts presents a 652 cc displacement delivering 35 kW (48 hp) at 6500 rpm and a max torque of 60 Nm at 5000 rpm. Optional accessories include output reduction for beginners to 25 kW (34 hp) at 6500 rpm and 47 Nm torque at 4500 rpm.
Unique on the single cylinder segment is the refinement, the product of a balancing shaft that suppresses vibrations to a great degree. Thanks to its closed loop three way catalytic converter and the BMS-C II engine management system, this dual ignition engine provides the best possible efficiency. For instance, the consumption at a constant 90 km/h is only 3.2 litres per 100 km. Ranges of 350 kilometres and more are possible. Not only environmental compatibility, also ride comfort and throttle response characterise this technology.
With a compression ratio of 11.5:1, this engine is designed for a fuel quality of min 91 RON, drawing its fuel-air mixture from an injection system. The injection is controlled and monitored electronically. This also ensures that the closed loop three way catalytic converter in the left silencer provides the optimum cleansing of exhaust gases. Delivering up to 48 hp, the G Series single cylinder engine transfers its power to a constant mesh five speed gearbox by means of a multiplate wet clutch.
Maximum clearance for offroad riding is provided by dry sump lubrication that distributes the oil. The modern cylinder head with four valve technology houses two overhead camshafts whose tappets act directly on the valve shafts.
The heat balance in the engine is regulated with 1.3 litres of coolant. The coolant level can be inspected conveniently through the port integrated in the left side. As is usual on the enduro segment, the secondary drive is transferred over an O ring chain. With 16/47 teeth (1:2.937), the secondary ratio is relatively small, but provides for the optimal acceleration, especially when the motorcycle is setting off or overtaking.
The single cylinder four stroke engine has a crankshaft made of separately compressed components which rotates within friction bearings in the vertically separable housing. Featuring an undivided lower eye, the connecting rod also has friction bearings. The slipper skirt piston runs in a nickel-silica-carbide coated bore that ensures minimal wear and tear and thus high mileage. The strong forces of inertia are neutralised by a balance shaft powered by spur gears and rotating counter to the crankshaft. Positioned at the front of the engine casing ahead of the crankshaft, it also drives the water pump.
Echoed in the motorcycle press, the engine concept behind these agile BMW Motorrad single cylinder models has particularly low vibration levels and a powerful torque.