BSA M20500

BSA M20500
Manufacturer	BSA
Production	1955 - 61
Engine	Four stroke, single cylinder, side valve
Compression ratio	4.9:1
Top Speed	80.5 km/h / 50 mph
Ignition	Magdyno
Battery	6 V (except for AA models: 12 V)
Transmission	4-Speed
Frame	Twin cradle
Suspension	Front: Up to 1947: Girder After 1947: Telefork Rear: None, spring loaded saddle
Brakes	Front: Drum, 7 in Rear: Drum, 7 in
Front Tire	3.25 x 19 in
Rear Tire	3.50 x 19 in
Wheelbase	1372 mm / 54 in (1937 model)
Weight	167 kg / 369 lbs (dry),
Oil Capacity	3.4 L / 7.2 US pints
Fuel Capacity	13.6 L / 3.6 US gal
Manuals	Service Manual

It could reach a top speed of 80.5 km/h / 50 mph.

Engine

The engine was a Air cooled cooled Four stroke, single cylinder, side valve. The engine featured a 4.9:1 compression ratio.

Drive

Power was moderated via the Multi-plate, dry.

Chassis

It came with a 3.25 x 19 in front tire and a 3.50 x 19 in rear tire. Stopping was achieved via Drum, 7 in in the front and a Drum, 7 in in the rear. The front suspension was a Up to 1947: Girder After 1947: Telefork while the rear was equipped with a None, spring loaded saddle. The M20500 was fitted with a 13.6 L / 3.6 US gal fuel tank. The bike weighed just 167 kg / 369 lbs. The wheelbase was 1372 mm / 54 in (1937 model) long.

Photos

Overview

BSA M20

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 BSA workers employed making the M20 were killed in an air raid on the BSA factory in Armoury Road, Small Heath, Birmingham on the night of Tuesday the 19th of November, 1940. The factory was one of the main targets for the Luftwaffe and at 9.25pm a low flying aircraft dropped two bombs which destroyed the southern end of the BSA building in Armoury Road. Rescuers included BSA's own fire brigade who pumped the Birmingham and Warwick canal dry putting out the fire. As well as 53 workers killed, 89 were injured and it was six weeks before the last of the bodies could be recovered. Much of the factory and equipment was destroyed or damaged but BSA had 67 factories so work was transferred elsewhere and production of the BSA M20 continued.

Modifications From October 1939 the K-M20 was designated the W-M20 and modified to include girder-forks and removal of the valanced rear mudguard. During late 1940 some civil specification M20s were purchased by the War Office which were civil models with a military paint scheme. In 1941 front and rear number plates were removed and between 1941 and 1942 active service use in North Africa showed the need for easy adjustment of the fork dampers. Special damper knobs were made of bakelite (later replaced with pressed steel). The DU142 headlight was replaced with a smaller 6 in Lucas DU42, with a hooded, slotted black-out shield, and a universal L-WD-MCT1A tail light was fitted.

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 The M20 failed on its first submission to the War Office in 1936 due to 'unacceptable engine wear'. The prototype machine required a replacement piston and cylinder after approximately 6,000 miles. In 1937 three more M20s were submitted to the War Office for testing. Two of these machines only just passed the 10,000 mile suitability tests at Military Vehicles and Engineering Establishment, MVEE, Chertsey, while a third machine was used in service trials. In 1938 when a small batch was commissioned. Criticised for being heavy and slow, with poor ground clearance it was saved by its reliability and ease of maintenance. As the need for transport quickly gained pace orders were placed for larger quantities. Most BSA M20 motorcycles were used by the British Army but the Royal Navy and the Royal Air Force also commissioned M20's from BSA. Designed as a general-purpose motorcycle for convoy escort and dispatch use, the M20 saw action in almost every theatre of war. After the war the BSA M20 model continued in military service throughout the national service of the 1950s and in smaller numbers until the end of the 1960s, partly due to the low cost and easy availability of spare parts but also as a result of six years of harsh conditions with no serious failures.

Civilian versions The BSA M20 was a reliable and affordable form of post war transport, so BSA repainted the khaki WD models black and they became particularly popular as a sidecar motorcycle. The Automobile Association placed a large order and their yellow and black M20 combinations became a familiar sight on British roads. The 1945 wartime cast iron engine continued in production until 1951, when an alloy cylinder head was introduced but otherwise it remained largely unchanged. Spares began to become harder to find in the 1950s, however, and the simple design was overtaken by modern twin cylinder motorcycles, so it was discontinued in 1956 — but the 600cc M21 went on until 1963 when it was also discontinued.

Make Model	BSA M20
Year	1955 - 61
Engine Type	Four stroke, single cylinder, side valve
Displacement	496 cc / 30.3 in
Bore X Stroke	82 x 94 mm
Cooling System	Air cooled
Compression	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 Tire	3.25 x 19 in
Rear Tire	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