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BSA M21

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