1985 BMW K 100 RS

developing its flat-twin boxer engine further:
·Developing European Union emissions regulations meant that more control was needed over the amount of fuel entering
the combustion chamber. From an engineering standpoint this was easier to
achieve with more cylinders at an overall smaller displacement.
·The market-led development of bikes was leading to the Japanese factories developing smoother
and quicker machines based around a four-cylinder format.
·Bike comparison in the media at the time was based around top speed, and a four-cylinder when fully
developed created more power.
In combination, this meant that BMW's marketing to users of a
superior bike, allowing them to price at a premium, was being quickly lost,
resulting in a loss of sales and market share.
The engine has its four cylinders arranged so that the crankshaft is on the right-hand
side of the motorcycle, with the cylinder heads, camshafts, injectors and spark
plugs on the left-hand side. This arrangement keeps the centre of gravity
relatively low, which benefits handling; and the space behind the front wheel
available for the radiator.
In addition, since the crankshaft is now on the right-hand
side, access to the engine becomes much easier than in a conventional design,
where the crankshaft is at the bottom. BMW preferred a shaft-drive for
smoothness, and a single-sided hollow swing arm enclosing the drive shaft
provided right side drive through the gearbox and to the rear wheel. The
4-into-1 all stainless steel exhaust exited on the left hand side.
Brakes were twin-potBremboonto undrilled discs. Two different
forks manufactures were used: Showa with an outer upper tube diameter of
1.612 in (41 mm) and Fichtel and Sachs measuring 1.627 in
(41 mm). In later models, the standard swingarm was replaced with aParaleverjust as on the K1