After World War I all German companies were prohibited from producing aircraft engines. Thanks to the manufacture of large displacement four-cylinder in-line engines for trucks, tractors and boats, they could be maintained, but a new product had to be created to ensure the future. Martin Stolle, a 34-year-old young engineer with great talent within the development department of BMW, had a brilliant that allowed the Bavarian house to get ahead.
Inspired by the engine that powered his Douglas motorbike, Stolle designed a 500cc air-cooled twin-cylinder impeller with horizontally positioned combustion chambers. This type of engine arrangement was already known as Boxer engine, in which the pistons always worked "one against one" similar to the movement of boxers in a fight.
In 1920 the production of the new Boxer engine began, which in its initial design generated 6,5 CV to 4.500 rpm. The brand new impeller was supplied to various motorcycle manufacturers under the name of Bayern-Kleinmotor (Small Bavarian Engine). Soon the idea of Stolle was installed in motorcycles of the brands Helios, Bison, SMW (Stockdorfer Motoren Werke), Corona y Hoco.
The most successful motorcycles were those made by Nürnberger Victoria-Werke, whose model KR 1 Powered by BMW's Bayern-Kleinmotor it attracted a large number of buyers. In this model alone, more than 1.000 copies of the first BMW Boxer engine were installed.
Two years after the launch of BMW's new bestseller, Stolle followed in the footsteps of “his” engine. He changed companies and moved to Victoria-Werke, where he participated in the development of other highly successful motorcycles.
In Munich his legacy was not only an innovative engine concept, but also a pioneering inspiration for the future of BMW. The company was destined to advance on two wheels.
After providing great proof of his mastery as an engineer with the aircraft engine IIIa, Max frizA BMW chief engineer, he was encouraged to explore new horizons and decided to develop a motorcycle in his own home.
The peace and quiet he needed for his project was found in the guest room of his house, located in front of the manufacturing plant. This is how, in December 1922, that quiet environment witnessed the birth of a new motorcycle. Its distinctive feature was the Boxer engine, combined with a robust cardan transmission, rather than a chain or belt. In addition, Friz attached the gearbox directly to the engine.
The result was a refreshingly harmonious motorcycle that was immediately well received. Internally known as R32, the first BMW motorcycle was presented to the public in September 1923.
La R37, introduced a year later, was marketed as Sportmodell. The model naming system known today was not introduced until the advent of the R42In 1926.
The Boxer engine configuration with cardan transmission and gearbox bolted to the engine is still valid today, on the motorcycles of the R Series from BMW, attesting to the legacy of Stolle and Friz, 100 years after the creation of the first BMW Boxer engine.