M20
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Make Model | M20 |
Year | 1955 - 61 |
Engine | Single cylinder, side valve, 4-stroke |
Capacity | 496 cc / 30.3 in |
Bore x Stroke | 82 x 94 mm |
Cooling System | Air cooled |
Compression Ratio | 4.9:1 |
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 |
Ignition | Magdyno |
Battery | 6 V (except for AA models: 12 V) |
Starting | Kick |
Max Power | 9.6 kW / 13 hp @ 4200 rpm |
Clutch | Multi-plate, dry |
Transmission | 4-Speed |
Final Drive | Chain |
Gear Ratios | Solo: 1st 15.8 / 2nd 10.9 / 3rd 7.0 / 4th 5.3:1 Sidecar model: 1st 17.6 / 2nd 12.2 / 3rd 7.8 / 4th 5.9:1 |
Frame | Twin cradle |
Front Suspension | Up to 1947: Girder After 1947: Telefork |
Rear Suspension | None, spring loaded saddle |
Front Brakes | Drum, 7 in |
Rear Brakes | Drum, 7 in |
Wheels | Steel, wire 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 (1937 model) |
Ground Clearance | 120 mm / 4.7 in |
Saddle Height | 724 mm / 28.5 in |
Dry Weight | 167 kg / 369 lbs |
Fuel Capacity | 13.6 L / 3.6 US gal |
Average Consumption | 4.3 L/100 km / 23.4 km/l / 55 mph |
Top Speed | 80.5 km/h / 50 mph |
Colours | Black and chrome with green tank and gold lining |
Source | Wikipedia |
At the outbreak of World War II BSA were Britain's largest motorcycle manufacturer with a long history of armaments supply to the armed forces. Designed by Val Page the BSA M20 started development in 1937 as a heavy-framed sidecar model with a simple 500 cc single cylinder side valve engine. It had low compression and plenty of low-end torque through a standard BSA gearbox.
Early K-M20 models from 1939 were made from standard civilian parts with the addition of military fittings, such as a large 8-inch Lucas DUl42 headlight (fitted with a black out mask), a timing-gear cover with a screw-in plug for access to the magneto drive-pinion nut and special filler caps for the petrol and oil tanks. These early military M20 models were also fitted with a long spiked prop stand on the rear nearside pivoted from a lug brazed on to the rear frame tube. Factory ledgers show that BSA exported K-M20 models to Sweden, South Africa and India, as well as civilian dealers and distributors.
M20 factory bombing From 1942 there was a shortage of rubber so handlebar grips and foot pegs were replaced by canvas covered metal items and production was standardised, with only minor modifications until the end of World War II. By early 1942 a new large rear carrier was fitted to hold universal WD steel pannier-frames and bags. This meant repositioning the long prop stand to forward of the nearside rear wheel spindle nut. In 1943 further modifications were made include redesign of the crankcase sump shield and fitting of the Vokes high capacity air cleaner, which was a box shaped canister on top of the fuel tank and was intended to assist operations in dusty environments. In early 1945 a push-button switch was introduced for the headlight and the main lighting switch relocated to a bracket beneath the offside of the saddle.
Military service
Civilian versions |