PUNCHING ABOVE THEIR WEIGHT – 100 YEARS OF BOXER ENGINES.

1918. The First World War has come to an end. The economy is on its knees and a ban on manufacturing aircraft engines has stripped BMW of its raison d’être. Time for a change of direction – such as producing engines for motorcycles, a mode of transport enjoying burgeoning popularity. A two-cylinder boxer engine provided the perfect solution for the job at hand, and series production duly got underway in 1920.

The first BMW boxer engine wasn’t designed for action in one of the company’s own machines but as a product to be offered to the array of motorcycle manufacturers plying their trade at the time. These firms were more small-scale workshops than large factory operations, their production numbers were fairly small and engine development was by a distance the most expensive piece in the overall jigsaw.

Boxer engine
BMW R 32
Boxer engine

A modest start.

Production of the M2 B15 (a.k.a. “Bayern-Kleinmotor” – small engine from Bavaria) began in winter 1920/21. Its most distinctive aspect was the flat arrangement of the cylinders – a signature feature of a boxer engine. At 494 cubic centimetres, the engine was no lightweight and it developed 6.5 horsepower. Nuremberg-based company Victoria deployed the new unit in its KR1 model with considerable success. Victoria had its cylinders positioned longitudinally, whereas BMW later preferred a transverse layout. This hallmark engine was introduced in the first motorcycle made by BMW itself – the R 32.

One of the principal creators of the first BMW boxer engine was Martin Stolle. Working alongside long-serving BMW designer Max Friz, Stolle felt undervalued and handed in his notice. The new engine he subsequently developed for one of the Bavarian company’s rivals promptly turned heads at Victoria – BMW’s most important customer – and sales at his former employer nosedived.

Franz Bieber at the Ruselbergrennen 1922 on Victoria KR1
MF 1798-1
Martin Stolle on Victoria KR1 1922

Merging into motorcycle construction.

BMW joined the ranks of motorcycle manufacturers overnight following its merger with BFW (Bayerische Flugzeugwerke) in 1921. BFW’s Helios and Flink models were only moderately successful, though, and even the arrival of the BMW engine in the Helios could do little to change that. A radical new solution was required, and fast. Managing Director Franz Josef Popp handed Max Friz the task of designing a complete motorcycle from scratch – and in a single month Friz presided over a mini-revolution. His still impressive 1:1 drawing shows a boxer engine facing crossways into the breeze, together with a cardan-shaft drive and double-cradle frame. This heralded the birth of the BMW R 32, which hit the roads in 1923, powered by the second boxer engine in BMW’s history.

The boxer engine became part of BMW DNA and is visually unmistakable. Like so much in life, it was created out of need; here, necessity really was the mother of invention. It set in motion a 100-year story of success unparalleled in the fast-moving world of engineering and technology. The sound, the looks, the broad grin on the face of the rider: these would become the hallmark characteristics of a BMW.