The S 1000 RR with the 1000 ccm four-cylinder in-line engine.

With an engine weight of just 59.8 kg, the engine is one of the lightest 1000 class four-cylinder engines on the market. Like all BMW motorcycle drives, this power train is based on a sophisticated overall design and a compact arrangement of all auxiliary assemblies as well as of the integrated, claw-clutch operated six-speed gearbox.

Given the task of creating a thoroughbred super sports drive, our engineers created a particularly compact engine with an ideal mass concentration around the motorcycle's total centre of gravity. Despite the large cylinder bore of 80 mm, the construction width at crankshaft height is just 463 mm. At 558 mm, it also has a very low construction height.

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The cylinder's vertical axis is inclined to the fore by 32 degrees. This results in an optimal centre of gravity and a front vehicle wheel-based weight distribution that is essential for supersport motorcycles for a precision driving feeling and the greatest possible front section feedback.
The crankshaft of the S 1000 RR drive is forged from a single piece of tempering steel and has the traditional 180 degree crank for uniform firing intervals. The con-rods on floating bearings are made of tempering steel for particularly light forged parts. At a length of 103 mm they enable a low, compact construction height of the power train that is beneficial for the centre of gravity with modest lateral forces on the pistons and yet still a quiet running engine. Two lubricated bores located in the upper con-rod eye at an angle of 45 degrees to the con-rod's vertical axis ensure the piston bolt bearing is supplied with oil. The con-rods are horizontally divided using the tried-and-tested cracking technique and thereby enable an extremely accurate fit on assembly without any additional centring.
Forged, lightweight, construction kit pistons with a diameter of 80 mm and a very short piston kit operate in cylinder bores with a Nikasil coating. They are equipped with two narrow piston rings optimised with respect to friction power and a three-part oil scraper ring.
The flat design of combustion chamber, piston base and valve reliefs supports a thermodynamically favourable combustion process and enables a weight-optimised piston base contour. The piston, complete with bolts and rings, weighs just 253 g. For heat discharge, the thermally high-loaded piston bases are target-cooled in the crankcase via oil spray nozzles. This ensures reliable operation even under extreme conditions and increases their service life.
The horizontal cylinder crankcase, which is split into two parts at the height of the crankcase's centre, is made of high-tensile aluminium alloy. The chilled-cast compact upper section forms a highly rigid bond from the four cylinders and the upper crankcase bearing seat. In addition the upper half of the casing holds the light and compact six-speed gearbox. The cylinder block with water jacket has what is known as a closed-deck design for maximum rigidity.
Performance capability, performance characteristics, combustion efficiency and fuel consumption are essentially determined by the cylinder head and the valve gear. The design of the four-valve cylinder head was developed with perfect channel geometry, compactness, optimal thermodynamics and an efficient thermal budget in mind. The narrow valve angle results in perfectly straight intake ports and a compact combustion chamber for a high rate of compression and optimal efficiency.
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The four-cylinder power train is equipped with cam follower control with two overhead camshafts for an optimal power output and maximum speed strength while at the same time fulfilling criteria for rigidity, minimal moved masses and optimal time cross-sections at the valves. It offers the perfect combination of maximum rigidity and minimal weight of moved valve gear components with a highly compact cylinder head design at the same time.
Valve clearance is compensated via very small, lightweight adjustment plates guided in the spring seats. On the intake side the spring seats are manufactured from lightweight high-performance aluminium. The moved masses of the cam follower valve control are lower than with a similar bucket-tappet solution. The low oscillating masses enable high valve acceleration for full cam profiles and high valve opening cross sections.
The speed limit defined for this series motorcycle is 14,200 r.p.m., though the purely mechanical speed tolerance is way above this. The large cylinder bore of 80 mm enabled the largest possible and therefore most performance-friendly valve disc diameters to be used. The valve disc diameters on the intake side are 33.5 mm, and on the exhaust side 27.2 mm, highly impressive as this is the greatest possible filling in the supersport 1000 segment.
For the lubricating system, the engine uses wet sump lubrication with an Eaton oil pump, a tried-and-tested solutions for this segment. In place of a heat exchanger, a separate oil cooler is used for oil cooling, which is integrated into the lower trim panel under the water cooler to aid flow aerodynamics. Use of an oil cooler prevents unwanted additional thermal pressurisation of the coolant, thereby enabling the use of a smaller and lighter water cooler and hence less coolant.
The focus here was on a lower construction width, a compact and, above all, lightweight construction and also on the arrangement of the electrical sub-assemblies and their drives. For instance, the alternating current generator is located on the left crankshaft stump and is equipped with a permanent magnet. It produces a power of 434 W at 6,000 r.p.m. and is designed for a maximum speed of 16,000 r.p.m. The transmission starter is capable of 800 W, weighs 1,050 g and is located in the left upper crankcase half behind the cylinders It is coupled via a freewheel and has a reducing effect at a ratio of 1:24.61 on the left outer crank-web, which is designed as a spur gear. To reduce weight, the left side cover for alternator and starter is manufactured from light magnesium.
Fuel injection works fully sequentially, i.e. the fuel is injected individually into the intake duct according to the intake stroke of the relevant cylinder. To improve the torque curve, the engine is equipped with sophisticated, controlled intake manifold technology. Depending on the speed, the length of the intake funnel is controlled by the characteristic map and varied in two stages via a servomotor attached to the intake silencer. The appropriate amount of fuel is added via four injector nozzles each located at the throttle-valve rail and above the intake pipe in order to obtain optimal filling. The fuel injector nozzles are actuated separately or together depending on speed and power requirement.
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