In 1983, the BMW K 100 became the marque’s first production motorcycle with a four-cylinder engine. Its 987cc unit produced 66 kW, or 90 PS, at 8,000 rpm, but the new series was also defined by its unusual mechanical layout.
The inline-four was mounted longitudinally and laid on its side. It used liquid cooling, Bosch LE-Jetronic fuel injection and two overhead camshafts. The engine also served as a load-bearing member of the tubular steel frame.
The gearbox bolted directly to the engine, while the single-sided rear swingarm housed the drive shaft. BMW called this integrated assembly the Compact Drive System. Alongside the new engine architecture, the familiar shaft-driven connection to the rear wheel remained.
The basic K 100 was unfaired; RS, RT and LT versions grew from the same foundation. Its history shows how one drivetrain design can underpin a whole motorcycle family, from a simpler roadster to versions equipped for long-distance travel.