The BMW M2B15 was BMW's first

flat-twin engine A flat-twin engine is a two-cylinder internal combustion engine with the cylinders on opposite sides of the crankshaft. The most common type of flat-twin engine is the boxer-twin engine, where both pistons move inwards and outwards at the same ti ...

. Manufactured from 1920 to 1923, the M2B15 was intended to be a portable industrial engine, but it was used by several German motorcycle manufacturers to power their motorcycles. In 1920, BMW engineer

Max Friz Max Friz (October 1, 1883 – June 9, 1966) was a German mechanical engineer specializing in engine design. He was the key contributor of engine design and innovation that led to the founding of Bayerische Motoren Werke AG (BMW) in 1917. Early ...

reverse-engineered Reverse engineering (also known as backwards engineering or back engineering) is a process or method through which one attempts to understand through deductive reasoning how a previously made device, process, system, or piece of software accompli ...

the engine of foreman Martin Stolle's 1914 Douglas motorcycle and developed a similar 500 cc side-valve

flat engine A flat engine is a piston engine where the cylinders are located on either side of a central crankshaft. Flat engines are also known as horizontally opposed engines, however this is distinct from the less common opposed-piston engine design, ...

from it. This was referred to internally as the Type M2B15 and offered for sale officially as the "Bayern Motor". The engine was tried out by various motorcycle manufacturers. Starting in 1920,

Victoria Victoria most commonly refers to: * Victoria (Australia), a state of the Commonwealth of Australia * Victoria, British Columbia, provincial capital of British Columbia, Canada * Victoria (mythology), Roman goddess of Victory * Victoria, Seychelle ...

Nuremberg Nuremberg ( ; german: link=no, Nürnberg ; in the local East Franconian dialect: ''Nämberch'' ) is the second-largest city of the German state of Bavaria after its capital Munich, and its 518,370 (2019) inhabitants make it the 14th-largest ...

used the engine in their KR 1 motorcycle, and other manufacturers such as SMW and Bison also fitted it. Bayerische Flugzeugwerke used the M2B15 engine in their Helios motorcycle. BMW inherited the Helios when it was merged with BFW in 1922.

References

M2B15 Motorcycle engines Boxer engines {{Motorcycle-stub