BMW M2B15

BMW M2 B15
BMW M2B15 at Deutsches Museum
Overview
Manufacturer	BMW
Also called	Bayern-Kleinmotor, Bayern Motor
Production	1920–1923
Combustion chamber
Configuration	flat-twin
Displacement	494 cc (30.1 cu in)
Cylinder bore	68 mm (2.7 in)
Piston stroke	68 mm (2.7 in)
Cylinder block alloy	cast iron
Cylinder head alloy	cast iron, in unit with block
Valvetrain	side-valve pushrod engine
Combustion
Fuel system	BMW carburettor
Fuel type	petrol
Oil system	wet sump
Cooling system	air-cooled
Output
Power output	6.5 hp (4.8 kW)
Dimensions
Dry weight	31 kg (68 lb)

The BMW M2B15 was BMW's first flat-twin engine. 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 reverse-engineered the engine of foreman Martin Stolle's 1914 Douglas motorcycle and developed a similar 500 cc side-valve flat engine 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 of Nuremberg 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.