BSA M21 (1937-61)

Make Model: BSA M21


Year: 1937 – 61
Engine: Four stroke, single cylinder, side valve,
Capacity: 591 cc / 36.1 in
Bore x Stroke: Up to 1938: 85 x 105 mm After 1938: 82 x 112 mm
Cooling System: Air cooled
Compression Ratio: 5.0:1
Oil Capacity: 3.4 L / 7.2 US pints
Carburetor: 1937-38: Amal 76, 1939-45: Amal 276, 1945 onward: Amal monobloc
Exhaust: Single, chrome
Induction: Aspirated
Ignition: Magdyno
Battery: 6 V (except for AA models: 12 V)
Starting: Kick
Max Power: 11 kW / 15 hp @ 4200 rpm
Clutch: Multi-plate, dry
Transmission: 4-Speed
Final Drive: Chain
Gear Ratios: Solo: 1st 14.3 / 2nd 9.9 / 3rd 6.3 / 4th 4.8:1 Sidecar model: 1st 16.6 / 2nd 11.5 / 3rd 7.3 / 4th 5.6:1
Frame: Twin cradle with integral sidecar lugs
Front Suspension: Up to 1947: Girder After 1947: Telefork
Rear Suspension: Up to 1947: None, spring loaded saddle After 1947: Plunger type

Front Brakes: Up to 1955: Drum, 7 in After 1956: Drum, 8 in
Rear Brakes: Drum, 7 in
Wheels: Steel, laced spokes
Front Tyre: 3.25 x 19 in
Rear Tyre: 3.50 x 19 in
Dimensions: Length: 2180 mm / 85.8 m Width: 740 mm / 29.1 in
Wheelbase: 1372 mm . 54 in.
Ground Clearance: 117 mm / 4.6 in.
Saddle Height: 724 m / 28.5 in.
Dry Weight: 167 kg / 369 lbs
Fuel Capacity: 13.6 L / 3.6 US gal


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