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In-line engine, two-cylinder, transverse mounted.

Since 2006, a new two-cylinder in-line engine design has been employed in the F model series. It is initially being incorporated in the F 800 S and ST models.
The engine, made largely of aluminium, is of a parallel twin design, with an ignition displacement of 360 degrees. This principle is characterised by particularly high power levels. It is clearly no coincidence that the resulting sound is reminiscent of that of the flat twin boxer.

In order to cope with the first and second order inertia moments that are unavoidably encountered in this type of engine, the BMW Motorrad engineers developed an unusual concept, aiming at an engine design that functions at a greater level of efficiency than one with standard, counter-rotating balance shafts. It is based on a system of articulated joints, positioned centrally on the crankshaft, comprising a pre-defined arrangement of counterweight masses. A balance rod sits on an eccentric, which is positioned at 180 degrees to the crank pins, and which is joined to an approximately vertical balance pivot. The precisely calculated distribution of masses between the piston-rod end and the balance pivot serves to efficiently oppose the oscillating inertia moments of the crankshaft, in all positions. They are effectively eliminated to the extent that only the pleasant pulsations of a powerful two-cylinder engine remain.

The water-cooled, 798 cm³ two-cylinder four-stroke engine has a highly modern cylinder head. A timing chain fitted with hydraulic chain adjusters drives two overhead camshafts, which control four valves for each cylinder via a system of cam followers.

The BMS-K engine management system is responsible, in conjunction with an intake injection and two 46-millimetre large throttle valves, for the preparation of the fuel mixture. The injection volume is determined by the duration of the injection sequence supplied by the fuel pump, and varies according to power requirements. By employing a pressure sensor, no return line is needed in the fuel supply system, since the amount of fuel transported is always precisely as required.

The oil circulation also displays an interesting special feature: as semi-dry sump lubrication is employed here, there is no need for a separate tank for engine oil; the effect of this is to eliminate mixture losses. Around 3 litres of lubricating oil is pumped around the engine, which means that at maximum rotational speed, oil is flowing through the system at a rate of approximately 20 litres per minute. An oil-water heat exchanger is additionally employed to reduce the engine oil temperature, which results in a rapid onset of the required operating temperature and commensurate shortening of the warming up period.

The compression ratio of 12.0:1 means that fuel consumption is highly efficient. Depending on the model, an average rate of 4.4 litres per 100 kilometres at 120 km/h can be attained, falling to 3.4 at 90 km/h. In conjunction with the 3-way catalytic converter, it effortlessly complies with the EU-3 norm.

The relatively long bore/stroke ratio of 82 x 75.6 millimetres ensures a good compromise between high-rev power and torque, while the power distribution figures of the models fitted with this engine are as impressive as the acceleration. Ninety percent of the maximum torque is available at 5,000 rpm, and as the engine speed moves up to the nominal level of 8,000 rpm, the curve continues to rise.

The total package which has been created here constitutes a highly modern broadband engine, which successfully demonstrates its many qualities with a variety of motorcycle designs.