The BMW F 800 R with the two-cylinder parallel-twin 800 ccm.

On the two-cylinder parallel-twin, the crankpin offset of the crankshaft is zero degrees. As a result the engine, which is installed horizontal to the riding direction, works with a uniform ignition sequence where one power cycle takes place with each turn of the crankshaft. This results in a sound that is deliberately similar to opposed-twin engines, which also work with an ignition offset of 360 degrees. In particular however the uniform firing sequence favors a balanced gas exchange with a high torque yield and harmonious characteristics. The basic prerequisites for a dynamic drive have therefore been met.

The inevitable mass forces with first and second order two-cylinder engines are neutralized using a previously unique balancing mechanism. Instead of conventionally via balancing shafts or counterweight shafts, the oscillating mass forces are compensated via a joint system guided centrally on the crankshaft with a defined arrangement of counterweight masses: an eccentric shaft arranged opposite the crank pin on the crankshaft bears what is known as a balancing con-rod. This con-rod is joined to a balancing swing arm.

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The kinematics are designed so that the balancing con-rod moves up and down in the opposite direction to the two engine con-rods. Due to the guidance via the relatively long swing arm, the piston rod end moves in a virtually straight swivel motion. The distribution of masses across the piston rod end and swing arm have been chosen so that the mass forces from the swivel motion in each crank position counteract the relevant oscillating mass forces of the crankshaft drive (piston and con-rod share). As a result the mass forces of first and second order are eliminated virtually entirely, resulting in low-vibration engine operation. A further major benefit of this elegant design is the low noise level, since no typical drive noises are emitted by gear wheels or chains.

The oil circuit also boasts special technical features, going beyond the conventional standard for the class. In order to minimize losses due to adulterants, the F 800 series of engines comes with semi-dry sump lubrication. The oil emitted from the main bearing of the crankshaft drive runs into the balancing mechanism's partitioned shaft. Here, an oil pump sucks the lubricant away and distributes it in the gearbox via oil nozzles. The oil that is drained from the gearbox via apertures in the crankcase collects, along with the oil drained from the cylinder head via the chain shaft, in the remaining free space in the crankcase around the con-rod shaft. This free space therefore serves as an integrated oil reservoir. All bearing positions are supplied from this reservoir via a second pump.

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In the two-cylinder parallel-twin engine of the BMW Motorrad F-series, there are two rotating overhead camshafts powered by a toothed chain. These actuate four valves per cylinder via cam followers. The entire valve gear is subject to extraordinarily low wear despite the large opening stroke, making maintenance intervals considerably longer.
Additional BMW-typical features include the mixture preparation, which is performed by an intake pipe fuel injection with BMS-KP-engine control and two 46 millimeter throttle valves. As well as via the injection time, the injection quantity is defined by the engine control via the pressure applied by the electric fuel pump according to the performance requirement. The fuel system works without oil return and merely pumps the quantity actually required by the engine. This delivery rate regulation saves on electricity and the fuel pressure can be modified across a broad area for optimal mixture formation. This principle is protected by means of patents and therefore unique. To gauge the fuel quantity added, as well as familiar parameters such as load, speed and temperature, the residual oxygen content in the exhaust gas is also used. The relevant information is provided by an oxygen sensor located behind where the manifolds join. This is essential for effective conversion of exhaust gases in standard three-way catalytic converters.
With the two-cylinder Parallel-Twin, BMW development engineers have deliberately focused more on smoothness and superior unfurling of power in the mid-speed range rather than on peak performances. The power train's acceleration will thrill sport riders while touring riders will enjoy the effortless shifting with the high-torque twin.
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