|BMW M2 B15|
|Displacement||494 cc (30.1 cu in)|
|Cylinder bore||68 mm (2.7 in)|
|Piston stroke||68 mm (2.7 in)|
|Block material||cast iron|
|Head material||cast iron, in unit with block|
|Valvetrain||side-valve pushrod engine|
|Fuel system||BMW carburettor|
|Oil system||wet sump|
|Power output||6.5 hp (4.8 kW)|
|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.
- Translation of BMW M2 B15 owner's manual
- Norbye, Jan P. (1984). "The Origins of BMW: From Flying Machines to Driving Machines". BMW - Bavaria's Driving Machines. New York, NY, USA: Beekman House. pp. 14–17. ISBN 0-517-42464-9.
- "M 2 B 15 "Small Bavarian Engine" (M15a)". BMW Classic: BMW History. Munich, Germany: BMW Group Classic. Retrieved 2012-08-11.
Construction time: 1920 - 1923
- Faloon, Ian (Feb 15, 2009). The BMW Boxer Twins Bible: All Air-Cooled Models 1970-1996 (Except R45, R65, G/S & GS). Veloce Publishing. pp. 6–7. ISBN 978-1-84584-1-683.
Coincidentally, BMW was also interested in motorcycles and in 1920 its foreman, Martin Stolle, stripped down his 1914 Douglas 500cc flat twin. Friz set about copying it, with a few modifications, and the BMW M2 B15 engine was born.
- Walker, Mick (2005-09-01). "1: Background". How To Restore Your BMW Twin: 1955-1985. Motorbooks Workshop (2nd ed.). p. 9. ISBN 978-0-7603-2262-8. Retrieved 2012-08-11.
The M2B15 was supplied to Victoria, Bison, SMW and SBD and other smaller companies.