Lightest and most compact serial production 6-cylinder in-line engine in a motorcycle > 1000 cc.
Previously, the in-line arrangement of six cylinders resulted either in very long or very wide constructions, depending on the installation position, which led to drawbacks in terms of chassis geometry, weight distribution and centre of gravity. The K 1600 models break new ground here.
The engine is significantly narrower in construction width than all other 6-cylinder in-line motorcycles in serial production to date. 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.
What is more, weighing 102.6 kilograms (basic engine including clutch, gearbox and alternator) the engine is by far the lightest serially produced 6-cylinder in-line engine for motorcycles in the class > 1000 cc.
Supremacy and ride comfort.
The transversely mounted 6-cylinder inline engine of the BMW K 1600 models has a capacity of 1649 cc. Its rated output is 118 kW (160 bhp) at 7 750 rpm. The maximum torque of 175 Nm is reached at 5 250 rpm. Over 70 per cent of the maximum torque is available from 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 this narrow construction, the electrical ancillary units and their drive mechanisms were moved behind the crankshaft into the free space above the gearbox.
This also made it possible create a powertrain with ideal mass concentration at the centre of the vehicle. The total width of the engine is 555 millimetres. This makes the engine only slightly wider than a current large-volume 4-cylinder engine.
Due to the perfect mass balance created by the construction, the 6-cylinder engine does not require a compensation shaft and the associated drive elements, which results both in weight benefits and increased running smoothness.
In its layout, the 6-cylinder in-line engine is based on the familiar 4-cylinder 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. The tilt of the engine likewise creates space for an aerodynamically optimised intake system directly above the engine, as well as allowing freedom for frame profile design geared towards optimum stability and rigidity.
Crankshaft drive and basic engine - narrow and light construction with six cylinders and a capacity of 1649 cc.
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 6-cylinder offset of 120 degrees for even firing intervals. Particular attention was also paid here to the issue of lightweight construction. For example the weight of the crankshaft is only very slightly in excess of a comparable 4-cylinder engine at just 12.9 kilograms The crankshaft is friction-bearing. The main bearing journals are 42 millimetres in diameter, while the connecting rod pin journals have a diameter of 40 millimetres. 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 other counterweights are aerodynamically optimised. 1
The drive of the camshafts in the cylinder head is effected by means of a tooth-type chain which runs via a compression-moulded 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 securing a low level of inner friction in this area. Horizontal partitioning is achieved by means of the well-established crack technology: the large connecting-rod eye is "cracked" in the centre plane by the specific hydraulic application of a powerful traction force. This rupture point enables extremely precise-fitting assembly without further centering.
Lightweight slipper pistons are used with a short piston skirt, two narrow piston rings optimised for frictional loss and a narrow oil scraper ring. The flat design of the combustion chamber means than in spite of the high compression ratio of 12.2:1 it has been 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 construction.
The dual-section cylinder crankcase is made of highly rigid aluminium alloys. The partition level is at the centre of the crankshaft. The compact upper section forms a highly rigid composite unit made up of the six cylinders and the upper bearing pedestal for the crankshaft. The use of the sand cast technique in the construction permits thin walls.
The cylinder block is designed in an open-deck construction, i.e. the water jacket is open to the cylinder head. The barrels have a wear-proof, low-friction nickel-silicon dispersion coating. The die-cast lower section forms the counterpiece to the main bearing of the crankshaft and supports the 6-speed gearbox. 2
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 4-valve cylinder head in the K 1600 models is geared towards 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 have opted for a valve operating system using bucket tappets. This combines the qualities of rigidity, compact construction and reliability.
The valve angle of the engine in the K 1600 GT and K 1600 GTL is 12 degrees on the intake side and 13 degrees on the exhaust side. The valve sizes are 29 millimetres on the intake side and 24.8 millimetres on the exhaust side, with a shaft diameter of 5 millimetres.
The two overhead shafts are powered by a tooth-type chain. This tooth-type chain drive is hydraulically tensed and damped, as well as being characterised by a high level of running smoothness.
The construction and manufacture of the camshafts represent an innovation in motorcycle engine construction. These are composite camshafts in which the individual cams are compression-moulded for positive coupling with the shaft, which is designed as a tube. The advantages as compared to conventional clear-chill cast camshafts derive mainly from the reduced weight, with around 1 kg being 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 order to reduce the weight of the drive unit as far as possible, the valve cover and the clutch cover are made of light magnesium. 3
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 even 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 6-cylinder in-line engine of the K 1600 GT and K 1600 GTL uses an integrated dry sump lubrication system. In addition to a high level of operating reliability, it allows a 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 construction. The oil reservoir forms an integrated oil tank in the rear section of the engine casing. A separate tank is therefore not required, which consequently has a positive effect in terms of the compact construction of the motorcycle and overall weight.
The dual oil pump is housed in the rear section of the engine casing and driven by cogs from the clutch shaft, circulating 4.5 litres of lubricant (engine oil capacity including filter change). It draws the lubrication oil from the oil reservoir and initially feeds it into the oil filter (full-flow filter) as pressure oil. The latter is located on the left lower crankcase side where it is easily accessible. From here the pressure oil reaches the main oil ducts in the crankcase and is distributed to the lubrication points via internal bores. The returning lubricant collects at the lowest point of the crankcase in the sump pan. The second pump supplies the returning oil to the oil cooler initially, and from here it flows back into the oil tank. The oil cooler is located below the headlamp in the front trim panel for optimum air flow. No monitoring of lubricant supply is necessary: if the oil level drops excessively, this is displayed in the instrument panel by means of an electronic oil sensor.
Carefully conceived cooling concept for maximum thermal stability.
A sophisticated cooling concept ensures perfect thermal balance in the 6-cylinder engine. Coolant flows transversely through the cylinder head. The intake of the cooling fluid is effected via the cylinder bank on the "hot" outlet 4
side. Precisely where the greatest thermal stress occurs, the intensive cooling at the cylinder head ensures rapid heat dissipation and therefore an excellent temperature balance. The diminished water flow at the cylinders reduces the warm-up phase and restricts cold-running wear-and-tear and friction, which also benefits fuel consumption. The coolant volume (50 % water, 50 % nitrite-free antifreeze) is 3.5 litres including 0.5 litres of levelling volume.
The water pump and the oil pump are powered 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. Due to the minimised frictional loss of the engine, the high degree of efficiency and the sophisticated aerodynamic design of trim and air flow, a comparatively small area of just 920 cc is sufficient for reliable heat dissipation in all conditions. The integrated thermostat keeps warm-up times as short as possible.
Ancillary units - alternator and starter.
In order to save construction space the electrical ancillary units and their drive mechanisms were moved behind the crankshaft into the free space above the gearbox. The three-phase generator is driven by the primary toothing of the clutch. The rated output of the generator is 580 watts, with a peak current of 57.5 ampere. With a view to optimising power consumption, the gear ratio of the crankshaft to the generate was fixed at 1:2.0. The reduction-gear starter is linked via a one-way clutch which acts on the generator drive gear.
Power transmission: narrow three-shaft transmission and self-energising clutch.
Torque is transmitted from the crankshaft to a 10-disc wet clutch via a straight-toothed primary drive.
Here the developers paid particular attention to a low level of control force at the hand lever. This is achieved by means of a self-energising mechanism in the clutch cage. When this is active, it may cause slight movements in the clutch 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 5
particular, it is designed as three-shaft transmission with three gearbox shafts arranged one on top of the other. The cogwheels are helical-cut, providing an excellent basis for low running noise.
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 rolling-bearing shift drum is hollow and made of a highly rigid aluminium alloy. The shift forks are made of steel and are lubricated with pressure oil.
Maintenance-free Cardan shaft drive at the rear wheel.
As in all large-volume BMW touring bikes, a drive shaft powers the rear wheel. The bevel gear at the gearbox outlet is housed in the gearbox cover. The entire rear-wheel drive is described in detail in section 3 "Chassis".
New engine control BMS-X.
The new BMW 6-cylinders feature the most state-of-the-art engine control to date. BMS-X is being used for the first time in the K 1600 GT and K 1600 GTL. Fully sequential, cylinder-selective injection for six cylinders, rapid processing of extensive sensor signals by means of state-of-the-art microelectronics, a compact layout, low weight and self-diagnosis are its most important features. Here BMW Motorrad extends its longstanding pioneering role in the area of electronic engine management.
The torque-based engine control with Alpha-n draws on a wide range of parameters. In this way it enables select torque delivery and a finely tuned adaptation of the engine to the most diverse conditions.
The control system is based on the volume of intake air which is determined indirectly via the throttle valve angle and the engine speed. From additional engine and environmental parameters (including engine temperature, air temperature and environmental air pressure), the engine control determines individually-adapted levels for injection volume and ignition timing together with stored mapping characteristics and pre-set correction functions. The fuel type is premium unleaded, i.e. at least 95 octane. 6
Ideal fuel dosage by means of variable pressure control.
The supply of fuel is effected on a needs-oriented basis via the control of the electrically regulated petrol pump with a pressure of 3.5 bar. The mixture composition is regulated by means of two oxygen sensors. These are positioned at the junction points of three exhaust manifolds and ensure precise registration of exhaust gas composition.
In the K 1600 GT and K 1600 GTL, the BMS-X integrates the functions of automatic idling-speed control and cold-start enrichment via the electronically regulated throttle valve. Idling speed increase during warm-up is carried out automatically by means of an increase in desired engine speed.
E-gas 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. The rider's wishes are registered by means of a sensor in the accelerator twist grip. The fully electronic engine control converts this command into a torque requirement within a fraction of a second and electronically regulates the throttle valve accordingly.
This makes it possible to achieve optimum ridability in the most diverse situations, as well as providing electronic cruise control and traction control. What is more, the use of the electromotive throttle actuator via various selectable modes also opens up new potential in terms of fuel consumption and riding dynamics. 7
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 intake silencer in perfect shape and position can be installed directly above the engine. With a volume of 8.5 litres, this intake silencer with upright panel air filter contributes to superior power delivery and high torque development. Air intake is via two air inlets which are fitted in the side trim section for optimum aerodynamic response.
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 BMW K 1600 GT and BMW K 1600 GTL result in a high degree of efficiency and therefore a low level of fuel consumption. In view of its power potential, the engine achieves top figures in this area, equivalent to the level of a comparable 4-cylinder motorcycle when a touring-oriented riding style is maintained. For example at a constant speed of 90 km/h, a fuel consumption level is achieved of just 4.5 l/100 km (K 1600 GT). This is largely due to the high geometrical compactness and the specific orientation of the in-line 6-cylinder engine towards maximum efficiency.
Exhaust system with 3-way catalytic converter and characteristic 6-cylinder sound.
Six individual manifolds of equal length come together under the gearbox, initially in two pipes which then lead into a large-volume rear silencer (6-in-2 system). The two silencers with oval section have a volume of 7.5 litres each and work according to the combined principle of reflection and absorption damping. The outer layer is thermally protected by the inner absorption layer.
At the points where the manifolds feed into the silencers there are metal-carrier catalytic converters with a cell width of 200 cpi (cells/inch²). By doing without a linking pipe it was possible to create a typical 6-cylinder sound, while of course still adhering to statutory requirements. In keeping with its 8
dynamic concept, the K 1600 GT sounds a shade more aggressive than the K 1600 GTL. While the two rear silencers in the K 1600 GT are made of brushed stainless steel, two chrome specimens reflect the luxurious style of the K 1600 GTL.
Three modes "Rain", "Road" and "Dynamic" to choose from for optimum adaptation to surface conditions and riding style.
The rider has three different engine characteristics 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. To make the required setting, the "Mode" switch on the right of the handlebar fitting is activated until the display in the instrument panel shows the desired mode. It is also possible to implement the rider's wish during travel and change modes by pulling the clutch lever and setting the throttle twist grip position to idle. When the motorcycle is restarted, the last selected setting is always maintained.
Both the K 1600 GT and K 1600 GTL can be fitted with DTC (Dynamic Traction Control as a special equipment feature ex works. Traction control DTC is combined individually with the different modes and fully harmonised with it so as to provide maximum riding safety.
For riding on wet surfaces with the resulting lack of grip, "Rain" mode offers a flatter, especially homogeneous output and torque curve (see section 8 "Engine output and torque"). The response and power delivery of the engine are particularly soft due to the altered electromotive throttle actuator parameters. In this mode, traction control DTC intervenes very early on before the frictional coefficient limit is reached, ensuring maximum safety for the rider even in difficult road surface conditions.
The rear wheel has sufficient lateral force to prevent break-away of the motorcycle rear section on wet, slippery surfaces. The ABS system remains unchanged in its settings.
For use on dry roads, "Road" mode provides full torque combined with a gentler, more touring-oriented accelerator response. This mode was developed for touring use on country roads and when travelling with a pillion 9
passenger. In this mode, DTC allows the vehicle greater controlled agility. The ABS system remains unchanged in its settings.
The "Dynamic" model was developed for sporty, dynamic use of the K 1600 GT and K 1600 GTL. Here again, the full torque is available, though the response to the throttle grip is entirely direct and perceptibly dynamic. Regulatory intervention of DTC is only effected when maximum power has been transferred to the rear tyre. The ABS system remains unchanged in its settings.