Lightest and most compact serial production six-cylinder in-line engine in a motorcycle.
Previously the in-line arrangement of six cylinders resulted in either very long or very wide constructions, depending on installation position, which in turn led to drawbacks in terms of chassis geometry, weight distribution and centre of gravity. This where the K 1600 models break new ground.

The engine is approximately 100 mm narrower than all previous serial production six-cylinder in-line engines used in motorcycle construction. This extremely compact construction and reduced width was achieved in particular by means of a just slightly undersquare stroke-bore ratio of 67.5 to 72 millimetres (0.938) with a relatively long stroke and very small cylinder centre distance spacings of 77 millimetres. The effective distance between the cylinder sleeves is thus only 5 millimetres.

Weighing 102.6 kilograms (basic engine including throttle valve, intake system, clutch, gearbox and alternator), the engine is by far the lightest serially produced six-cylinder in-line engine for motorcycles.

Supremacy and drive comfort.
The transversely mounted six-cylinder in-line engine of the BMW K 1600 models has a capacity of 1649 cc. Its rated output is 118 kW (160 bhp) at approx. 7 500 rpm. The maximum torque of approx. 175 Nm is reached at approx. 5 000 rpm. 70 per cent of maximum torque is available from just 1 500 rpm. The development goals here were highly superior touring characteristics and ridability combined with maximum running smoothness.

Compact overall design and space-saving construction.
In order to achieve the narrow construction, the electrical ancillary units and their drive units were shifted behind the crankshaft into the free space above the gearbox. This also made it possible create a drivetrain with ideal concentration of masses at the centre of the vehicle. The total width of the engine is 560 millimetres. This means that the engine is only slightly wider than a current large-volume four-cylinder in-line power unit.

Due to the perfect mass balance created by the construction, the six-cylinder engine does not require a compensation shaft and the required drive elements, which results both in weight benefits and increased running smoothness.

In its layout, the six-cylinder in-line engine is based on the familiar fourcylinder in-line engine of the K 1300 series and, like the latter, has a cylinder axis which is tilted forwards by 55 degrees. This not only results in a low centre of gravity but also a balanced weight distribution of 52 to 48 per cent (K 1600 GT unladen) - imperative for a precise ride feel and transparent feedback of the front section when driving dynamically. The tilt of the engine also creates space for an aerodynamically optimised intake system directly above the engine, as well as providing the ideal frame profile design in accordance with the distribution of forces.

Crankshaft drive and basic engine - narrow and light construction with six cylinders and 1649 cc capacity.
The crankshaft of the K 1600 engine is a single-piece construction forged in heat-treated steel. It has counterweights and inertia-optimised discs as well as the usual six-cylinder offset of 120 degrees for even firing intervals. Particular attention was also paid here to the issue of lightweight construction, so the weight of the crankshaft is only vey slightly in excess of a comparable four-cylinder engine at just 12.9 kilograms. The crankshaft is friction-bearing. All main bearings are supplied directly with pressure oil. The lubrication supply to the connecting-rod bearing comes from the main bearings.

One of the crankshaft web counterweights acts as a cogwheel for the primary drive to the clutch. Another cogwheel on the outer crankshaft web is used for engine speed sensing. The drive of the camshafts in the cylinder is effected by means of a tooth-type chain which runs over a compressionmoulded toothed chain wheel on the right-hand end of the crankshaft. The friction-bearing connecting rods are light forged parts made of heat-treated steel. Measuring 124.45 millimetres in length, they benefit smooth engine running and ensure low lateral forces in the pistons, thereby ensuring a low level of inner friction in this area. The well-established crack technology is used for horizontal partitioning.

Lightweight slipper pistons with a short piston skirt, two narrow piston rings optimised for frictional loss and a narrow oil scraper ring are used. The flat design of the combustion chamber means that in spite of the high compression ratio of 12.2:1, it was possible to keep the piston head and piston relief flat. This supports thermodynamically favourable combustion and enables a weight-optimised piston head shape.

Horizontally separated case in open-deck design.
The dual-section cylinder crankcase is made of highly rigid aluminium alloys. The partition level is at the centre of the crankshaft. The compact sand-cast upper section forms a highly rigid composite unit made up of the six cylinders and the upper bearing pedestal for the crankshaft.

The cylinder block with water jacket is designed in open-deck construction, the running surfaces having a wear-resistant, low-friction nickel-silicon dispersion coating. The die-cast lower section forms the counterpiece to the main bearing of the crankshaft and carries the six-speed gearbox.

Cylinder head with barrel camshafts and bucket-type tappets.
The output, characteristics, efficiency and therefore fuel consumption of engines are largely determined by the cylinder head and valve gear. The design of the chill-cast four-valve cylinder head in the K 1600 models GT and GTL is designed for optimum channel geometry, compactness, excellent thermodynamics and a reliable heat balance.

With a view to maximising inspection intervals in particular, the BMW Motorrad engine experts opted for a valve operating system using bucket tappets. This also combines the qualities of rigidity, compact construction and reliability.

The two overhead shafts are powered by a tooth-type chain. The tooth-type chain drive is hydraulically tensed and damped, and is characterised by a high level of running smoothness.

The design and manufacture of the camshafts represents an innovation in motorcycle engine construction. They are composite camshafts in which the individual cams are compression-moulded for positive coupling with the shaft, which has a tubular design. The advantages as compared to conventional clear-chill cast or steel camshafts derive mainly from the reduced weight. Around 1 kilogram is saved here. The rotational speed limit defined for serial production is 8 500 rpm, though the purely mechanical rotational speed tolerance is much higher.

In the attempt to reduce the weight of the drive unit as far as possible the valve cover and the clutch cover are made of light magnesium.

High compression for maximum efficiency.
A tight valve angle enables a very compact combustion chamber with a flat calotte, thereby providing the basis for a high geometrical compression ratio of 12.2:1 with a thermodynamically favourable, largely evenly designed piston head. This high level reflects the effectiveness of the combustion chamber design in terms of achieving an ideal combustion process and optimum efficiency.

Integrated dry sump lubrication for optimum oil supply.
The six-cylinder in-line engine of the K 1600 GT and GTL uses an integrated dry sump lubrication system. In addition to providing a high level of operating reliability, it enables flat construction of the crankcase and therefore a lower installation position of the engine and a concentration of masses close to the centre of gravity. This makes it possible to do without a conventional oil sump with oil reservoir, so the engine can be placed much lower in the vehicle than would be the case with a conventional design. The oil reservoir forms an integrated oil tank in the rear section of the engine casing. A separate tank is therefore not required, which again has a positive effect in terms of the compact construction of the motorcycle and overall weight.

Carefully conceived cooling concept for maximum thermal stability.
A sophisticated cooling concept ensures perfect thermal balance in the sixcylinder engine. Coolant flows transversely through the cylinder head. The intake of the cooling agent is effected via the cylinder bank on the "hot" outlet side, which is also cooled in this way. Precisely at the point where the greatest thermal stress occurs, the intensive cooling at the cylinder head ensures rapid heat dissipation and therefore an excellent temperature balance. The reduced water flow at the cylinders reduces the warm-up phase and reduces coldrunning wear-and-tear and friction, which also benefits fuel consumption.

The water pump is powered together with the oil pump by the primary drive via cogwheels. The radiator is trapezoid and curved in shape and housed in the trim at the bottom front to optimise the centre of gravity.

Power transmission: narrow three-shaft transmission and selfenergising clutch with anti-hopping function.
Torque is transmitted from the crankshaft to a self-energising 10-disc wet clutch with anti-hopping function via a straight-toothed primary drive. Here, the developers paid particular attention to a low level of control force at the hand lever.

The gearbox complete with bevel gear is integrated in the engine casing. In order to reduce construction width in the area of the rider footrests in particular, the gearbox is designed as a three-shaft transmission with three gearbox shafts arranged one on top of the other. The cogwheels are helicalcut, enabling a particularly low level of running noise to be achieved.

Shifting between transmission stages is effected by means of a shift drum, shift forks and shift sleeves to achieve a force-fit connection. In order to save weight, the hollow shift drum is made of a highly rigid aluminium alloy and supported by antifriction bearings.

E-Gas (ride-by-wire) for excellent response and precise fuel dosage.
The control of the central throttle valve with a diameter of 52 millimetres is effected via an E-Gas, also known as a ride-by-wire system. This means that the rider's wishes are transferred directly from the sensor in the accelerator twist grip. The fully electronic engine management system converts this command into a torque requirement and electronically regulates the throttle valve accordingly.

The sensing of all factors in terms of torque makes it possible to achieve optimum ridability in the most diverse situations, as well as enabling electronic cruise control and traction control. The use of the electromotive throttle actuator via various selectable modes also opens up new potential in terms of fuel consumption and riding dynamics.

Intake system with long tract lengths for excellent torque.
The central throttle valve enables the achievement of long induction tract lengths, which benefits an especially full torque development in the lower and medium engine speed ranges - a desirable characteristic in a touring bike. For example, some 125 Nm of torque is already available at 1 500 rpm.

The heavily tilted engine position means that an air box in perfect shape and position can be installed directly above the engine. With a volume of 8.5 litres, the air box with upright panel air filter contributes to superior power delivery and high torque development.

Low fuel consumption due to efficiency optimisation.
Low engine speed level, high gas velocities, efficient combustion and minimised frictional loss in the engine of the K 1600 GT and GTL result in a high degree of efficiency and therefore a low level of fuel consumption. The exact fuel consumption figures will be announced at a later date. In view of its power potential, the engine achieves top figures in this area, which are at the level of a comparable four-cylinder motorcycle when a touring-oriented riding style is maintained. This is largely due to the high geometrical compactness and the orientation of the in-line six-cylinder engine towards maximum efficiency.

A choice of three modes - "Rain", "Road" and "Dynamic" - for optimum adaptation to surface conditions and riding style.
The rider has three different riding modes available at the press of a button at the right-hand end of the handlebars ("Rain", "Road", "Dynamic") so as to be able to adapt to different uses such as touring on the road, riding on wet surfaces and dynamic motorcycling.

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