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The over-riding requirements for this motor by BMW were to try and keep it compact, light and efficient. After some amount of research on different layouts and types, BMW came to the conclusion (somewhat reluctantly I suspect) that the across the frame inline four was the best format for this type of bike.
Okay, so an inline four cylinder with DOHC and four valves per cylinder is not exactly a revolutionary design, but there are some interesting ideas incorporated into the new K1200S motor:
LOW AND COMPACT
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| Lean it over 55 degrees. |
Unhappy with the high centre of gravity of the conventional inline four designs, BMW incorporated a 55-degree forward lean angle into the cylinders of the K1200S. This moves more of the load toward the front wheel and opens up space above for a large airbox, as well as giving freedom of frame design (no requirement for it to go around the motor).
By making the motor a dry sump design and slapping the alternator behind the cylinders instead of on the end of the crank, they have also managed to keep the overall width and height of the motor to a minimum. This enables a low mounting of the motor, while maintaining lean clearance (50 degrees) and aiding a low c of g.
Okay, that’s all fine and dandy, but what’s going on inside then?
