The BSA M20 was a British

motorcycle A motorcycle (motorbike, bike, or trike (if three-wheeled)) is a two or three-wheeled motor vehicle steered by a handlebar. Motorcycle design varies greatly to suit a range of different purposes: long-distance travel, commuting, cruising ...

made by Birmingham Small Arms Company (BSA) at their factory in

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Birmingham Birmingham ( ) is a city and metropolitan borough in the metropolitan county of West Midlands in England. It is the second-largest city in the United Kingdom with a population of 1.145 million in the city proper, 2.92 million in the West ...

. Although initially viewed as a near failure by the

War Office The War Office was a department of the British Government responsible for the administration of the British Army between 1857 and 1964, when its functions were transferred to the new Ministry of Defence (MoD). This article contains text from ...

in 1936, the M20 evolved into one of the longest serving motorcycles in the history of British military motorcycling, as well as becoming the most numerous type produced for

World War II World War II or the Second World War, often abbreviated as WWII or WW2, was a world war that lasted from 1939 to 1945. It involved the vast majority of the world's countries—including all of the great powers—forming two opposin ...

with 126,000 in active service. Many are still in use around the world today.

Development

At the outbreak of

BSA were Britain's largest motorcycle manufacturer with a long history of armaments supply to the armed forces. Designed by

Val Page Valentine Page (1891–1978) 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 Sweden, formally the Kingdom of Sweden,The United Nations Group of Experts on Geographical Names states that the country's formal name is the Kingdom of SwedenUNGEGN World Geographical Names, Sweden./ref> is a Nordic country located on ...

South Africa South Africa, officially the Republic of South Africa (RSA), is the southernmost country in Africa. It is bounded to the south by of coastline that stretch along the South Atlantic and Indian Oceans; to the north by the neighbouring countri ...

and

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, 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,

on the night of Tuesday 19 November 1940. The factory was one of the main targets for the

Luftwaffe The ''Luftwaffe'' () was the aerial-warfare branch of the German ''Wehrmacht'' before and during World War II. Germany's military air arms during World War I, the ''Luftstreitkräfte'' of the Imperial Army and the '' Marine-Fliegerabtei ...

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 Polyoxybenzylmethylenglycolanhydride, better known as Bakelite ( ), is a thermosetting phenol formaldehyde resin, formed from a condensation reaction of phenol with formaldehyde. The first plastic made from synthetic components, it was developed ...

(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

. 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 including 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 The Military Vehicles and Engineering Establishment (MVEE) was a British defence research unit on Chobham Lane, Chertsey in Surrey. It was responsible for many innovations in armoured vehicle design, including ceramic Chobham armour. History T ...

, MVEE,

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, 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

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but the

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and the

Royal Air Force The Royal Air Force (RAF) is the United Kingdom's air and space force. It was formed towards the end of the First World War on 1 April 1918, becoming the first independent air force in the world, by regrouping the Royal Flying Corps (RFC) and ...

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 National service is the system of voluntary government service, usually military service. Conscription is mandatory national service. The term ''national service'' comes from the United Kingdom's National Service (Armed Forces) Act 1939. The ...

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.

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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.

112 MPH BSA M20

As well as being painstakingly restored by enthusiasts to accurate wartime specification, the M20 has also been developed by specialists for speed trials. A 1938 BSA M20 ridden by Bill Jenkins from

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achieved a top speed of 108 mph at

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making it the fastest M20 in the world. The original side-valve engine was extensively modified and fuelled with

nitrous oxide Nitrous oxide (dinitrogen oxide or dinitrogen monoxide), commonly known as laughing gas, nitrous, or nos, is a chemical compound, an oxide of nitrogen with the formula . At room temperature, it is a colourless non-flammable gas, and has a ...

. The intake port fed by the carburetor, originally horizontal, was re-drilled at a steep angle into the cylinder casting so it pointed up at the underside of the intake valve. The motorcycle did however retain the long BSA prop stand that hinged under the seat and clipped to the rear mudguard when not in use — so it looked like a stock M20. In October 1995 an M20 fitted with a

BSA Gold Star The BSA Gold Star is a motorcycle made by BSA from 1938 to 1963. They were 350 cc and 500 cc single-cylinder four-stroke production motorcycles known for being among the fastest bikes of the 1950s. Being hand built and with many op ...

crankshaft sprocket and running on a 95% methanol / 5% acetone mix ridden by Pat Jeal achieved a terminal speed of 112 mph at the disused airfield of

RAF Elvington Royal Air Force Elvington or more simply RAF Elvington is a former Royal Air Force station which operated from the beginning of the Second World War until 1992 located at Elvington, Yorkshire, England. History Royal Air Force use The station ...

, Yorkshire.

References

External links

BSA wartime gallery

Video of BSA WD M20
{{WWIIBritishSoftVeh M Military motorcycles Motorcycles introduced in the 1930s Articles containing video clips World War II vehicles of the United Kingdom Single-cylinder motorcycles