Motorcycle specifications BMWK 100 1983 BM's first 4

BMW has built the legend of the flat-twin. Although the single-cylinder is a recurrent theme in the brand's history, it is the architecture of its flat-twin that remains its indelible trademark.

Yet innovation regularly shakes up this kind of saga. In the history of motorcycling, certain machines mark a breakthrough. The BMW K 100 falls into this category. For the public accustomed to the Flat, the arrival of this bike was a surprise, a daring gamble that divided purists but paved the way for the modern BM era. Nicknamed the "Flying Brick" because of the shape of its engine, it embodied a technical and philosophical revolution that helped renew interest in the brand.

The genesis of a daring gamble

In the early 1980s, BMW was faced with a dilemma. Its R-series, with its air-cooled, twin-cylinder boxer engine, was beginning to look dated in the face of more sophisticated, high-performance Japanese competition. To remain relevant, the Bavarian brand needed to innovate. Rather than fine-tune its existing engines, it took a radical decision: to design an entirely new motorcycle, with a novel engine architecture.

The result was the K 100, a motorcycle powered by a longitudinal in-line 4-cylinder engine, mounted flat in the frame. Transmission was by shaft rather than chain, a BMW specificity retained. This engine block, with its forward-facing cylinders, resembled a brick laid on its side, earning it its nickname.

Avant-garde engineering

The 987 cm3 water-cooled 4-cylinder engine was the first of its kind for BMW. It featured Bosch L-Jetronic electronic fuel injection, a rare technology on a production motorcycle at the time. With 90 hp at 8,000 rpm and torque of 8.7 m.kg at 6,000 rpm, it offered smoother power delivery and a very different torque distribution from the boxer engines of the day.

Its compact design, with the main driveshaft integrated into the engine block, ensured remarkable robustness, making the K 100 a motorcycle capable of covering hundreds of thousands of kilometers without trouble.

Despite weighing 239 kg (dry), the K 100 was renowned for its excellent balance and handling. Its low center of gravity, thanks to the flat-mounted engine, gave it reassuring stability, even at high speeds.

The Monolever rear suspension, a BMW innovation, was one of the bike's strong points. This single-arm swingarm connected directly to the engine and universal joint transmission eliminated the notorious "universal joint torque" of earlier R models, which tended to lift the bike under acceleration. The system ensured a smoother ride and better roadholding.

A trio of revivals

The K 100 was available in several versions to meet different needs. The basic K 100, a streamlined roadster; the K 100 RS (for Reise-Sport), which added an aerodynamic fairing and half handlebars for a sportier ride; and the K 100 RT (Reise-Touring), which offered a full fairing, an adjustable windscreen and a more upright riding position.

The bike was one of the first to offer ABS as an option, a major safety innovation long before it became the norm. Fuel injection was not widely used, and the position of the engine made a lasting impression.

The "Brick" had to convince

Despite its many qualities, the K 100 was not without its faults, often pointed out by critics and owners alike. While the engine was smooth at high revs, it suffered from noticeable vibrations at low revs, a phenomenon that was only partially resolved on later models.

Despite its low center of gravity, the K 100 was a heavy bike. Its heavy weight could make it difficult to maneuver from a standstill or at very low speeds.

For brand purists, the K 100 lacked the soul and mechanical character of the old boxers. The sound of the engine, though powerful, was more classic, more "Japanese", and less distinctive than that of the flat-twin engines.

Other problems, often minor but recurrent, were reported by owners: the fragility of the fuel pump immersed in the tank, or difficult starting in cold weather on certain models. However, these shortcomings did not detract from the car's reputation for reliability.

A new path

The BMW K 100 paved the way for a whole line of K models, from the surprising K1 to the LT, which muscled up the road-going category. Much later, the 4-cylinder became the S in the Bavarian catalog, while the ^fixed K gained nobility by becoming synonymous with the 6-cylinder. But that's another story.

M.Bi. - Manufacturer's photos