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BMW M2 B15
BMW M2B15 at Deutsches Museum
Also calledBayern-Kleinmotor,[1]
Bayern Motor[2]
Displacement494 cc (30.1 cu in)
Cylinder bore68 mm (2.7 in)[4]
Piston stroke68 mm (2.7 in)[4]
Cylinder block materialcast iron[4]
Cylinder head materialcast iron, in unit with block[4]
Valvetrainside-valve pushrod engine[4]
Fuel systemBMW carburettor[1]
Fuel typepetrol
Oil systemwet sump[1]
Cooling systemair-cooled
Power output6.5 hp (4.8 kW)[2]
Dry weight31 kg (68 lb)[1]

The BMW M2B15 was BMW's first flat-twin engine.[3] Manufactured from 1920 to 1923, the M2B15 was intended to be a portable industrial engine,[2] but it was used by several German motorcycle manufacturers to power their motorcycles.[5]

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.[4] This was referred to internally as the Type M2B15 and offered for sale officially as the "Bayern Motor".[2] The engine was tried out by various motorcycle manufacturers. Starting in 1920, Victoria of Nuremberg used the engine[2] in their KR 1 motorcycle,[3] and other manufacturers such as SMW and Bison also fitted it.[5]

Bayerische Flugzeugwerke used the M2B15 engine in their Helios motorcycle. BMW inherited the Helios when it was merged with BFW in 1922.[2][4]


  1. ^ a b c d Translation of BMW M2 B15 owner's manual
  2. ^ a b c d e f 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.
  3. ^ a b c "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
  4. ^ a b c d e f g h 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.
  5. ^ a b 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.