BSA M series

In the 1930s the M series was a mixture of overhead valve and side-valve models. During and after the Second World War only the side-valve models of this series were continued, typically for use by the armed forces or in sidecar combinations.

BSA M33-10 ( M34-12, M35-10, M10 )
The BSA M33-10 was a British motorcycle made by BSA at their factory in Small Heath, Birmingham in 1933.

The M33-10 was developed as a 5.95 hp side valve based on the earlier BSA Sloper with capacity extended to 595cc to make it more suitable for use with a sidecar. In 1934 M33-10 was replaced by the M34-12 'de Luxe' side valve and the M34-13 overhead valve 'de Luxe' models, bith of which had 5.95 hp engines.
All BSA Motorcycles M Series

Model		Engine	First year	Last year	Notes
M33-10, M34-12, M35-10, M10		596 cc	1933	1936	Side-Valve
M33-11, M34-13, M35-11		596 cc	1933	1935	overhead valve
M19 Deluxe		349 cc	1937	1938	overhead valve
M22		496 cc	1937	1939	overhead valve
M23 Silver Star/Empire Star		496 cc	1937	1940	overhead valve
M24 Gold Star		496 cc	1938	1939	overhead valve
M20		496 cc	1937	1955	side-valve. Thousands of this model were supplied to the British Army
M21		591 cc	1937	1963	side-valve. The UK's Automobile Association used this model in sidecar combinations
M33		499 cc	1947	1957	B33 overhead valve engine in M series plunger frame for civilian sidecar work

M33-10, M34-12, M35-10, M10 596 cc 1933 1936 side-valve M33-11, M34-13, M35-11 596 cc 1933 1935 overhead valve M19 Deluxe 349 cc 1937 1938 overhead valve M22 496 cc 1937 1939 overhead valve M23 Silver Star/Empire Star 496 cc 1937 1940 overhead valve M24 Gold Star 496 cc 1938 1939 overhead valve M20 496 cc 1937 1955 side-valve. Thousands of this model were supplied to the British Army M21 591 cc 1937 1963 side-valve. The UK's Automobile Association used this model in sidecar combinations M33 499 cc 1947 1957 B33 overhead valve engine in M series plunger frame for civilian sidecar work