800 ccm two-cylinder in-line engine.
The high-torque parallel-twin engine with a displacement of 798 cubic centimetres is common to all F-models. Its high torque characteristics, which are similar to an opposed-twin engine, unique sound and spontaneous kick with each rev combines the liveliness of a single-cylinder with the irrepressible force of two. Besides attaining a balance between powerful torque and dynamic sprint-ability, the newly developed parallel-twin engine proves that excellent driving performance need not necessarily be associated with high levels of fuel consumption.
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 driving 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 favours 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 neutralised 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.
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 minimise 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.