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BSA B21

Make Model	BSA B21
Year	1937 - 39
Engine	Four stroke, single cylinder, Overhead valve
Capacity	249 cc / 15.2 cub in
Carburetor	Amal
Oil capacity	2.3 L / 4.8 US pints
Exhaust	Single, chrome silencer
Ignition	Magneto
Battery	6V
Starting	Kick starter
Transmission	4-Speed, hand change
Final Drive	Chain
Gear Ratios	1st 18.2 / 2nd 12.4 / 3rd 8.1 / 4th 6.2
Frame	Triangulated cradle type
Front Suspension	Girder, spring loaded fork
Rear Suspension	None, spring loaded saddle
Wheelbase	1575 mm / 62 in.
Ground Clearance	124 mm . 4.9 in.
Fuel Capacity	13.6 L / 3.6 US gal

In the 1930s Birmingham's BSA was the world's most productive manufacturer, with a stretch of models between 150cc and 1000cc, produced in single cylinder and/or vee twin configurations. They enjoyed a particular strength in the quarter litre class, with a variety of side- and overhead valve models, offered in standard or de-luxe spec, one of the latter's options being foot-change gearbox operation.

Due to a disastrous attempt at the TT, back in the early 1920s, BSA deliberately avoided any forms of competition for the greater part of the Thirties, in complete contrast to their post war philosophy. Even so, in a contemporary magazine road test impression the B21 in question was reported to have 'peppy' performance and, "...contrary to its sturdy appearance was found surprisingly easy to manoeuvre on to the rear stand".