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4-cylinder transverse inline engine

For the K models K 1200 GT, R, R Sport and S, starting BMW Motorrad has developed a completely new 4-cylinder in-line engine . With a bore/stroke ratio of 79 x 59 mm and a piston speed of over 21 m/s at rated engine speed, the completely aluminium engine is designed as a purebred high-performance power unit.

For the first time in the history of BMW Motorrad, the 4-cylinder engine of the K 1200 S is mounted transversely, with an extreme forward tilt of 55 degrees. This method of installation lowers the motorcycle' centre of gravity, at the same time an optimum static wheel load distribution of 50:50% is achieved for sporty riding. The low position of the engine also creates space for large-size airbox placed directly above the engine for an aerodynamically favourable arrangement of the two intake ducts.

In this way, the intake system of the K 1200 S combines the classic resonance tube induction system - ensuring a fuller torque curve - with the benefits of ram induction, thereby increasing top output at high speeds.

The 1,157 cc short-stroke engine lives up to expectations. The 4-cylinder engine with its 123 kW (167 bhp) at 10,250 rpm catapults the K 1200 S from 0 to 100 km/h in just 2.8 seconds. The maximum thrust of the K 1200 R (120 kW / 163 bhp) is truly impressive at 127 Nm. The sportiest BMW motorcycle engine of all times really pulls at its rider's arms from around 8,000 rpm, before the speed limiter puts an end to further revving at around 11,000 rpm. At the same time, the 4-cylinder engine with maximum torque of 130 Nm at 8,250 rpm develops impressive pulling power from idling and provides supple throttle response across the entire engine speed range. It thus ensures outstanding performance figures and supreme pulling power at all engine speeds. In order to achieve improved performance during fast touring, the engine of the K 1200 GT has been designed for more powerful torque, now delivering 112 kW (152 bhp) at 9500 rpm.

One particular technological superlative is the narrow construction of the new 4-cylinder engine, measuring just 43 centimetres at the height of the crankshaft - i.e. equalling the level of a modern 600 cc 4-cylinder engine. The power unit can thus be positioned deep in the frame without impairing the banking freedom a rider expects from a sports motorcycle. The reduced width of the engine also allows an extremely favourable positioning of the water pump to the left of the cylinder head, where it is powered directly by the intake camshaft. The tubes to the radiator can thus be kept very short.

Further weight reduction is achieved by means of light materials: for example the clutch cover is made of magnesium. With a total weight of just 81.5 kg, (incl. clutch, gearbox, starter, generator and shaft drive), the new 4-cylinder aluminium engine sets the benchmark in its capacity class.

The engine block is bolt-fastened to the aluminium frame at seven points so as to give the chassis additional rigidity. The outstandingly neutral handling of the K models reflects the effectiveness of this construction principle. This effect is supported by the sophisticated dry sump lubrication with its extremely flat oil pan. Since the oil supply is not underneath the engine, the engine - and thus the motorcycle's centre of gravity - has been lowered further towards the road. At the same time, the dry sump lubrication ensures optimum engine lubrication even in extreme situations on the road.

In order to achieve the performance figures of this high-tech 4-cylinder, BMW Motorrad engineers drew on the BMW Group's long years of experience in Formula 1 racing. For example, the cylinder head is derived directly from Formula 1, with the 16 valves powered by the two upper camshafts. This solution is particularly sound for high revving and allows compact construction of the cylinder head. The low moving masses and the extreme rigidity of the valve control system also ensure reduced strain on the individual components - the most important requirement for reliability and durability in an engine.

Other technical highlights such as the aerodynamically optimised intake and output ducts, digital engine electronics (BMS-K) and the high compression ratio of 13:1 (with cylinder-selective knock control) not only make for high performance but also ensure an impressively harmonious power delivery. At the same time, two balancer shafts reduce the free inertia forces which are characteristic of a 4-cylinder in-line engine to a minimum. Reduced vibrations means increased comfort for the rider, allowing both rider and passenger to enjoy long journeys without tiring.

The exhaust emissions are purified in a four-in-one exhaust system weighing just 10.4 kg by means of a rhodium-coated catalytic converter characterised by high temperature resilience and durability. Together with the secondary air system, this ensures that the currently valid exhaust gas limits are easily adhered to.

The new 4-cylinder is not only the most powerful engine ever to power a serial production BMW motorcycle, it also sets new standards in its capacity class with numerous innovative solutions, compact dimensions and low weight.