BMW R 1200 GS Powertrain







Published by Gerald Ferreira Date: October 4, 2012
Categories: BMW, BMW Motorcycles, Motorcycles

Completely newly designed engine for maximum riding dynamics in the travel enduro segment.

BMW R 1200 GS 2012

Like all engines in BMW motorcycles, the details of the boxer engine in the R 1200 GS are based on a carefully conceived overall concept. Designed to perpetuate the almost 90-year tradition of the BMW boxer engine with a future-oriented concept created to hold good for years to come, the engine reproduces numerous classic engineering features but also offers a wealth of new technical solutions. The strengths of the boxer have been further refined for the new BMW R 1200 GS so as to achieve a greater breadth of application in terms of touring suitability, dynamic performance and off-road qualities.

While the previous boxer power unit itself provided supreme forward thrust in all situations, the new BMW R 1200 GS takes a significant step further. With its completely redesigned engine it offers a much higher level of dynamic performance, acceleration and pulling power across the entire engine speed range, both on the road and over rough terrain.

The totally newly developed 2-cylinder opposed-twin in the R 1200 GS has a capacity of 1170 cc as in the predecessor model. The ratio of bore to stroke of 101 to 73 millimetres has also been preserved. The rated power output is 92 kW at 7700 rpm, and its maximum torque of 125 Nm is available at 6,500 rpm.

The foremost development goals for the new engine were top-level riding dynamics within the segment, characteristics favouring both sporty and touring requirements, optimum ridability, compact dimensions and the lowest possible weight.

The empty weight (ready for the road) according to DIN of the R 1200 GS is 238 kg including standard BMW Motorrad Integral ABS.

BMW R 1200 GS 2012 Powertrain

Compact air/water cooling for optimum heat management.

The performance aspired to, as well as adherence to future anticipated requirements in terms of noise and exhaust emissions, is ensured among other things by a change in the cooling system. The boxer engine in the new R 1200 GS continues to use air/liquid cooling but the oil coolant has been replaced by a glycol water mixture for the first time in a BMW Motorrad boxer engine. This ensures a high level of heat absorption capacity of the coolant for more efficient heat dissipation.

So-called precision cooling means that the cooling fluid flows through the thermally more heavily exposed engine elements - the two cylinder heads and parts of the cylinders. Heat dissipation is via two radiators positioned at the left and right of the front section. These are inconspicuously integrated and well protected by the radiator covers. An electric fan behind the right-hand radiator is automatically activated as needed, controlled by the thermostat - for example at high outdoor temperatures in city traffic. Thanks to the sophisticated cool-air ducting on both sides, the warm air is streamlined past the rider.

The engine still also uses air cooling which reduces radiator size and preserves the characteristic appearance of the boxer engine.

With the new very compact cooling system, it has been possible to significantly improve the cooling ratio and thus the heat management system as compared to the predecessor model (22 % oil cooling / 78 % air cooling) in the new BMW 1200 GS (35 % liquid cooling / 65 % air cooling). The new liquid cooling adds weight to the vehicle as compared to the previous air/oil cooling system, but due to its very compact size and high efficiency, this is only a very moderate addition of approx. 2.7 kilograms.

Cylinder heads with vertical through-flow for increased efficiency and performance.

The engine of the new BMW R 1200 GS has vertical through-flow unlike all previous standard BMW Motorrad opposed-twin engines. The advantage is that the design of the intake channel no longer depends on the camshaft control, so it was possible to realise identical intake lengths for both cylinder sides. What is more, the fuel injector in the intake port is now arranged so that the fuel can be injected as squarely as possible in front of the intake valves for optimum carburetion. The result is a higher level of power and torque efficiency across the entire engine speed range as well as improved fuel efficiency.

As in the predecessor model, the two camshafts made of heat-treated steel are arranged horizontally. By changing the through-flow direction from horizontal to vertical, however, it is now possible to have purebred intake and exhaust camshafts - in the predecessor model these were combined intake/exhaust camshafts. This also opens up the possibility of adding variability to the valve gear in future. Newly calculated cam profiles allow a reduction of overlap time without impacting on performance.

As before, the two respective camshafts are driven by a chain running in the shaft behind the cylinders (on the right-hand side of the engine from the counterbalance shaft and on the left from the crankshaft). The timing chain drives an intermediate shaft between the intake and exhaust camshaft and it is from here that power is transmitted to the camshafts via spur gear pairs. At each exhaust camshaft there is an centrifugal-force-driven decompression facility which facilitates the start-up process. This makes it possible to save weight in the starter motor and battery.

Compared to the hitherto horizontal through-flow of the cylinder heads, the vertical through-flow permits an optimally straight intake port with a correspondingly simple chain guidance of the camshaft drive.

Due to the highly efficient overall design of the power unit, the previous radial valve arrangement is no longer required. At 8 degrees on the intake side and 10 degrees on the exhaust side, the four valves are at close angles to one another, making for a compact combustion chamber shape - a feature which is crucial to optimum combustion. Due to the new calculation of the combustion chamber and the much improved channel ducting and design, it has been possible to improve the compression ratio as compared to the predecessor model from 12.0:1 to 12.5:1. What is more, due to the optimisation of the combustion process and ignition timing, no knock control is required, despite retaining the RON 95 set-up, while still making the most of torque potential.

The use of a turbulence system (air feed via a bypass) ensures optimum combustion, obviating the need for an elaborate dual ignition.

The plate diameters of the valves have also been redefined to obtain higher output and torque efficiency. They are 1.0 millimetres larger, with a size of
40 millimetres on the intake side and 34 millimetres on the exhaust side. The valve stem diameter is still 5.5 millimetres as before. Significantly shorter valve springs do justice to the increased engine speed level, while also ensuring an optimally defined drag effect.

As before, the valves are operated via light, speed-resistant rocker arms, the design of which was derived from the high-performance 4-cylinder engine of the BMW S 1000 RR. The valve clearance settings are made by means of replaceable shims. With 0.10 to 0.17 millimetres on the intake side and 0.34 to 0.41 millimetres on the exhaust side, valve clearance levels are just below those of the predecessor model.

Basic engine with compact, light and yet rigid crankshaft.

The crankshaft has also been completely re-engineered. The main bearing diameter was reduced from the previous 60 millimetres to 55 millimetres to reduce the drag forces. The crankshaft also has crankpins which are narrower but with a diameter enlarged from 48 to 50 millimetres as well as narrower main and guide bearings. As a result, it is lighter overall yet much stiffer and more compact.

Although the boxer principle, with its opposed cylinders, offers mutual cancelling out of the free mass-forces (due to the rods and pistons moving back and forth), there is still a certain amount of residual vibration. This results from the unavoidable parallel offset of the two cylinder axes, meaning that the forces do not act precisely on the same level and resulting in a so-called rotating mass moment of inertia.

This rotating mass moment of inertia has been significantly reduced by means of a more compact crankshaft design, but it was not possible to eliminate it completely. As in the existing boxer engine of the R 1200 GS, the new engine therefore also has a counterbalance shaft which runs at crankshaft rotation speed with newly defined imbalance masses so as to eliminate unwanted vibrations. The counterbalance shaft is designed as a hollow intermediate shaft within which the clutch shaft runs. This ensures that the new engine of the R 1200 GS, with its higher engine speed level, runs more comfortably and with perceptibly less vibration across the entire engine speed range and at high engine speeds in particular. Nonetheless, the essential earthy boxer characteristics are still preserved.

Vertically separated case in open deck construction.

For the first time in a BMW Motorrad boxer engine, the cylinders are no longer separately bolted to the crankcase, but are integrated directly. The dual-section die-cast cylinder crankcase with vertical split level at the centre of the crankshaft is made of highly rigid aluminium alloy. The two case halves form a highly rigid composite consisting of the cylinder and the bearing block for the crankshaft.

The cylinder with cooling jacket is designed in open deck form. The liners are coated with a low-wear and low-friction iron-carbon alloy using the new wire arc spray process (LDS) already used for BMW automobile engines.

Gearbox integrated in engine housing for the first time, including wet clutch with anti-hopping function.

For the first time in the history of BMW Motorrad, the gearbox and clutch are integrated in the engine housing of a boxer engine. This provides benefits in particular in terms of weight balance due to the omission of numerous bolt connections and sealing surfaces, but also in terms of the torsional response of the unit as a whole. In addition to saving space and weight, the new gearbox (two transmission shafts, one drive shaft, one output shaft) means there is no longer any need for the additional transmission oil volume previously required for lubrication.

The 6-speed gearbox of the new R 1200 GS was also redefined to meet the demand for light, precise shifting and optimum gearshift connections so as to achieve excellent riding dynamics. As a result, the ratios were newly calculated.

As before, a helical gearing system is used for the gearwheels which ensures low running noise and a high level of running smoothness due to smooth tooth engagement. As before, the gear shafts of the new engine are mounted on anti-friction bearings and the gearwheels (idlers) run smoothly on needle roller bearings. Shifting of the gearwheels and therefore of the gears is effected by means of a ball-bearing mounted selector drum made of steel, three case-hardened gearshift forks with hard chrome-plated ends and sliding sleeves with force-fitting connections between the gearwheel pairs.

The new R 1200 GS is the first serial production BMW Motorrad boxer motrcycle to have a multiplate wet clutch with eight friction discs instead of the previous single-disc dry clutch. The benefits of this solution lie in the reduced moment of inertia, on the one hand due to the significantly reduced external diameter of 147 millimetres (R 1200 GS previously: 180 mm), but also in its more compact size.

For the first time in conjunction with a boxer engine, the clutch system is fitted with an anti-hopping mechanism. Here, BMW Motorrad especially addresses the needs of ambitious riders of the new R 1200 GS travelling on country roads. The brake torque of the engine is now passed to the rear wheel at a reduced level during coasting. This prevents brief blocking or hopping of the rear wheel due to the dynamic wheel load distribution when applying the brakes heavily and changing down at the same time. In this way, the motorcycle remains stable and safely controllable in the braking phase. Clutch disengagement during coasting is effected mechanically by means of a ramp mechanism. The clutch is activated hydraulically.

The practically oriented level of hand force and finely sensitive controllability provided by hand force enhancement in the clutch ensure that the high standards of BMW Motorrad are met in terms of operation and comfort. In conjunction with the sensitive throttle response, this makes for optimum vehicle control on all types of terrain.

New intake system for excellent output and torque.

For more than two decades now, BMW Motorrad has occupied a leading position in the field of electronic engine management, and in the case of the new R 1200 GS this is taken care of by the new digital engine control system, the so-called BMS-X.

Its main features are fully sequential injection, a compact layout and low weight. The Alpha/n-based engine management system with torque interface draws on a wide range of parameters. For example, it enables perfectly controlled torque output and adaptation of response to a diverse range of conditions via the E-gas characteristics attributed to the various riding modes. The control system is based on the volume of intake air which is determined indirectly via the throttle valve angle and the engine speed. Based on additional engine and environmental parameters (including engine temperature, air temperature and environmental air pressure), the engine control system determines individually adapted levels for injection volume and ignition timing together with stored mapping characteristics and pre-set correction functions.

Carburetion is taken care of by an electronic fuel injection system via a throttle valve body system with an opening width of 52 millimetres instead of the previous 50 millimetres. Newly designed, markedly raised intake air snorkels and a generously sized airbox with panel air filter element ensure optimum feeding of cool intake air and thus optimum filling.

E-gas for improved ridability, running smoothness and special functions.

An electromotive throttle actuator system is used to control the two throttle valves. Here the rider’s commands are passed on directly from the sensor in the accelerator twist grip to the fully electronic engine control system and converted into a throttle valve position as appropriate to the riding mode selected by means of instant electronic adjustment.

The electromotive throttle actuator in the new BMW R 1200 GS allows improved ridability and optimised running smoothness in the near-idling range since the engine control detects any differences between the two cylinders in terms of mean pressure and compensates by means of selectively adapting the throttle valve angles. Furthermore, in conjunction with the optional ASC and riding modes, different throttle response characteristics can be set (soft, optimum, direct) according to the intended purpose.

Much improved controllability has enabled a reduction of twist grip angle from 85 to 70 degrees. Another advantage of this technology is the realisation of a cruise control function as a comfort option.

Electronic cruise control.

The new R 1200 GS is the first BMW GS  to be available with an electronic cruise control function fitted ex works - making lengthy motorway rides more relaxed and comfortable, for example. The function is activated by pressing a button at the left-hand end of the handlebars, while a shift paddle is used to increase or reduce the currently selected road speed. Here the two throttle valves are activated by the engine control and independently of the accelerator twist grip.

When the front or rear brake or the clutch are activated or the throttle grip is turned in the opposite direction (starting from the idling position) cruise control is switched off. The “Resume” function allows the rider to re-activate the originally selected speed, which the vehicle then automatically restores. As long as the drag torque in the currently selected gear is sufficient, the electronic cruise control function works on hill descents, too.

Innovative exhaust gas system with electronically controlled exhaust flap for optimum performance characteristics and an earthy boxer sound.

The exhaust system of the new R 1200 GS is made entirely of stainless steel and geared completely towards optimum performance characteristics, operating according to the 2-in-1 principle. In this development area, homogeneous output and torque curves and thus excellent ridability were once again regarded as requirements for supreme performance on country roads, off-road riding and extended touring.

The two manifold tubes and the interference pipe were redesigned in terms of shaping, length and diameter. The new BMW R 1200 GS meets the demand for a particularly earthy yet still legally compliant boxer sound with an exhaust flap controlled by an electric motor along with opening and closing cables. In order to reduce ram pressure and ensure a full sound, the rear silencer - now positioned on the right-hand side - has a completely newly engineered interior structure, which uses a combination of reflection and absorption silencing.

Exhaust emissions are regulated by means of an oxygen sensor controlled catalytic converter. In this way the BMW R 1200 GS meets current exhaust emissions standards and is designed to meet future standards, too.

Optimised lightweight cardan shaft drive with EVO Paralever swingarm now running on the left-hand side.

For 90 years, BMW Motorrad has used the universal-shaft drive as a logical consequence of longitudinal crankshaft mounting - the optimum maintenance-free form of power transmission for a travel enduro.

In contrast to all previous BMW Motorrad boxer models, the swingarm with integrated cardan shaft drive and EVO Paralever (in its third generation and designed using the very latest calculation methods) is now positioned on the left-hand side. This avoids any contact between the rider and the hot exhaust system when pushing or getting on and off the machine. Another pleasing effect relates to the appearance of the vehicle: when the motorcycle is on the side stand there is now a clear view of the redesigned rear wheel. A newly calculated set of bevel/crown gears for the drivetrain meets increased output and torque requirements. In the tried and tested manner, the Paralever swingarm decouples the unavoidable reactive torque of the drivetrain from the swingarm and therefore from the suspension/damping system by means of an additional joint between the rear axle cover and the swingarm. This effectively eliminates the undesirable “elevator effect”, i.e. the rising and lowering of the rear when accelerating and decelerating.

As part of the complete redesign of the drive system, there has also been a comprehensive reduction of clearance from the primary drive to the drivetrain, causing the enhanced engine performance to act more directly on the rear wheel.

ASC and riding modes as an optional extra: five freely selectable modes - “Rain”, “Road”, “Dynamic”, “Enduro” and “Enduro Pro” with three different characteristic throttle curves.

In order to suit various purposes such as riding on the road, on wet surfaces or over rough terrain, an ex works option is available to the rider of
the new R 1200 GS which comprises five different riding modes with three different E-gas settings, three different ABS settings and four ASC settings. To make the required setting, the “Mode” switch on the right of the handlebar unit is activated until the display in the instrument panel shows the desired riding mode. It is also possible to implement the rider’s command during travel: the mode change is made by moving the throttle twist grip to idle with the clutch lever pulled. When the motorcycle is restarted, the last selected setting is always maintained.

The optional feature includes Automatic Stability Control (ASC) in a special enduro configuration for the “Enduro” and “Enduro Pro” modes. A special enduro configuration for the standard BMW Motorrad ABS is also featured – this is also used in the “Enduro” and “Enduro Pro” configurations. Dynamic ESA as an optional feature is then also integrated in the system of modes. Suspension set-up is adjusted precisely depending on the riding mode selected (see Suspension section).

When riding on wet surfaces or in difficult grip conditions, “Rain” mode provides especially soft dosage and response characteristics to support the rider, though full torque and output potential are still retained. The electronic control system ASC (Automatic Stability Control) responds more readily than in “Road” mode. If the Dynamic ESA option is selected, the damping of the spring struts at front and rear is softer, in keeping with the conditions.

In “Road” mode, the control systems are set to ensure optimum performance on dry roads. This mode provides a spontaneous, linear throttle response on dry roads. “Road” combines sound, supple controllability with a homogeneous build-up of torque.

“Dynamic” mode reveals the sportiest face of the new BMW R 1200 GS for road riding. An even more spontaneous and direct throttle response, more restrained ASC intervention and tighter damping in the case of the Dynamic ESA option bring the full potential of the machine to bear.

The “Enduro” mode enhances the R 1200 GS for off-road riding. A soft throttle response, restrained control intervention on the part of the Enduro ASC, optimum brake distribution and ABS control in conjunction with the high-traction set-up of the optional Dynamic ESA get the motorcycle ready to explore new enduro worlds. This means that even motorcyclists with limited enduro experience will quickly get their off-road bearings on the new R 1200 GS and enjoy lots of riding fun. The mode is optimised for use with standard tyres.

For more ambitious enduro riders, BMW Motorrad offers the “Enduro Pro” mode. This riding mode provides spontaneous engine response characteristics and is designed for use with studded tyres. At the same time, the ABS function is disengaged at the rear by pressing the footbrake lever; the optional Dynamic ESA shifts into traction-oriented and optimum bottom-out set-up. ASC is set to professional enduro mode and permits considerably more slip. In this configuration, the sporty face of the new BMW R 1200 GS is revealed off-road, too, and the experienced enduro rider can move into an added dimension of riding fun due to further improved controllability of the machine.

About the BMW R1200 GS