BSA B series

The B-series were single cylinder models of 250cc, 350cc and 500cc. After the Second World War only 350cc and 500cc overhead valve models were continued.


The BSA B21 was a British motorcycle made by Birmingham Small Arms Company (BSA) at their factory in Small Heath, Birmingham. Production started in 1937 and ended with the outbreak of World War II in 1939. Development After World War I, BSA started designing new models and began exporting motorcycles to the colonial countries. During the depression of the 1930s, the BSA range was reduced and in 1937 Val Page designed the B21 250cc and the M23 Empire Star in both 350cc and 500cc engines. When the second world war started, the Military BSA M20 with a side valve engine of 500cc took over and the B21 was discontinued.
The BSA Blue Star is a British motorcycle made by BSA at their factory in Small Heath, Birmingham. The Blue Star range was produced between 1932 and 1936. In 1936 a slightly uprated sports version called the BSA Empire Star was launched with the Blue Star remaining in the model range. In 1937 an entirely new engine designed by Val Page featured in the Empire Star and the Blue Star was dropped from the range. The Empire Star developed into the famous Gold Star in 1938 (also known as the M24).
The B33-3 O.H.V. 249cc Blue Star was called the Blue Star Junior and the R33-5 348cc O.H.V. Blue Star was known as the Sporting Blue Star. It was the W33-8 499cc O.H.V. that became the most popular, however, and led to the development of the Gold Star.It was known as the "sea beezer" and it was BSAs fifth best seller.
Further information:BSA B series Pre-unit construction

Model	Engine	First year	Last year	Notes
B33-1 - B35-1, B1	249 cc	1933	1936	side-valve
B33-2 - B35-2, B2	249 cc	1933	1936	overhead valve
B33-3 - B35-3, B3 Blue Star	249 cc	1933	1936	overhead valve
R33-4 - R35-4, R4	349 cc	1933	1936	overhead valve
R33-5 - R35-5, R5 Blue Star	349 cc	1933	1936	overhead valve
W32-6, W33-6, W34-7, W35-6, W6	499 cc	1932	1936	side-valve
W32-7, W33-7, W34-8, W35-7	499 cc	1932	1935	overhead valve
W33-8, W34-9, W35-8 Blue Star	499 cc	1933	1935	overhead valve
W33-9, W34-10, W35-9	499 cc	1933	1935	overhead valve
B20	249 cc	1937	1938	side-valve
B21	249 cc	1937	1939	overhead valve
B22 Empire Star	249 cc	1937	1938	overhead valve
B23	348 cc	1937	1939	side-valve
B24	348 cc	1937	1939	overhead valve
B25	348 cc	1937	1939	overhead valve
B26	348 cc	1937	1939	overhead valve
B29	348 cc	1940		overhead valve
B30				overhead valve
B31	348 cc	1945	1959	overhead valve
B32	348 cc	1946	1957	overhead valve
B33	499 cc	1947	1960	overhead valve
B34	499 cc	1947	1957	overhead valve