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Memorable Motorcycles: BSA M20 Despatch

Thursday, November 22, 2012
Ease of maintenance  simple engineering and the use of cast iron and pressed steel made the BSA M20 an appealing choice for the British military.
Ease of maintenance, simple engineering and use of cast iron and pressed steel rather than scarce aluminum made the BSA M20 an appealing choice for the British military.
I need to begin this episode of Memorable Motorcycles with a disclaimer. To save all the military vehicle experts writing letters of complaint, I do know that the BSA M20 featured in this article is not a technically perfect example of a British Despatch rider’s bike. I also know how important supremely accurate detail is to war buffs so please accept that this M20 is in the spirit of a Despatch bike – rather than being an award winning example of one.

The M20 has two interesting facts attached to it. First, it was the most widely built military motorcycle of the Second World War, with a shade over 126,000 units produced. Second, despite the huge numbers of M20s which were manufactured, it was not the most popular motorcycle with the troops who rode into battle. Almost every BSA rider would have dumped their M20 in a ditch, at the first opportunity, in order to have the vastly better Matchless G3L.

Given the fact that there were better motorcycles available to the British forces, what then made the bike such a success?

The M20 story goes back to 1936 and Britain’s greatest motorcycle designer ever, Val Page. I am a huge fan of Valentine Page, and the M20 either shows that he was having a bad day at the office or, more likely, BSA management had really put the knuckle screws on him in terms of cost cutting.

The BSA M20 might not look flashy  but it would get you home.
The BSA M20 wasn't flashy and not the most off-road capable mount from BSA. However, it could claw its way out of slippery situations and proved reliable for war-time duty.
The aim was to produce a dull as ditch water, 500cc side-valve Single with a lot of torque. The job of this unworthy steed would be to plod around British roads, pulling a sidecar which would contain Mum, three kids and the family dog. When you realize that BSA were only claiming 13 hp for their new 500 you can see that this was not intended to be a hot sports set-up.

When the bike was first submitted to the Ministry of Defence in 1937 it was rejected, with both the piston and cylinder barrel failing after 6000 miles.

The second batch of prototypes was better, just scraping through the 10,000 mile minimum target and a small lot of M20s were ordered in 1937. There was a tremendous irony in the order. The M20 was heavily criticized by the evaluation team at the Mechanisation Experimental Establishment at Farnborough for being slow, heavy and possessing an extremely low ground clearance.

This should have been the death knell for any prospective order but the MEE test staff did like the bike’s reliability and ease of maintenance. They were also rather fond of the M20’s huge pulling power – a combination of a low, 4.9:1 compression ratio, heavy flywheels, long (94mm) piston stroke and ultra-mild valve timing.

The four-speed, wide-ratio gearbox was also well received. Thoughtful of the overall gearing, first was perfect for plodding through mud while top gear still allowed the Despatch rider to make brisk progress carrying vital documents. This latter task was very important when field radios were still heavy, clumsy and unreliable.

Though designed for road use  the BSA M20s were surprisingly reliable off-road as well.
Designed primarily for road use, the BSA M20 was tossed into off-road conditions as well.
Meanwhile, the off-road experts at BSA were far from happy at the thought of the M20 in military service. While the management was pushing the British government to order the M20, BSA’s highly influential development rider, Bert Perrigo, was vociferously against the idea.

Perrigo proposed the overhead valve BSA Blue Star which was lighter, faster and vastly better off-road than the M20. Army riders competing in trials for the official Army team had the even better M24 Gold Star which they had used to success in international, long-distance events. So, if there were so many superior alternatives, why the M20?

One reason, and a critical one, was the materials and engineering used in the M20. Even by the standards of the day, the M20 was low tech and easy to manufacture. Most importantly, the bike contained very little aluminum. This was a vital factor when one considers that at the start of the war British housewives were being urged to donate their pots and pans to make Spitfires: the shortage was that severe. Therefore, a motorcycle with a cast iron barrel and cylinder head and pressed steel brake hubs was always going to be desirable.

The engine was basic beyond belief and was simple to manufacture. No special machine tools were required and assembly was equally simple. Again, this was critical when skilled craftsmen were being drafted into the military and new staff had to learn skills very quickly.

British Despatch rider with his BSA M20 in the field.
British Despatch rider with his BSA M20 in the field.
Because there was nothing new on the bike, sub-contractors were not placed on unfamiliar and challenging ground. The girder forks were simple to make and not subject to the demands of very fine tolerances, while brazed lug frames had been made by BSA since the very start of motorcycle production.

If something did break, it could be repaired simply in field workshops by competent military mechanics who did not need to be experts in motorcycles.

A further factor was BSA’s ability to make lots of M20s very quickly - and to do so while under severe strain. In 1939, BSA controlled 67 factories, employed 28,000 people and used over 25,000 machine tools. So when the main BSA factory at Small Heath was bombed during the 1940 Blitz, production was not terminally damaged.

The key fact that BSA could make the M20 in such large quantities was the one thing that prevented British and Commonwealth forces from being equipped with a better military motorcycle. What the military logistics officers wanted was a small inventory of spares which could be sent anywhere in the certainty that they would be supplying M20s.
The statistics are quite startling. During the war years, all the British factories combined produced 289,666 motorcycles of all capacities and types and of this total 126,334 were M20s. For sure, wherever the British were engaged in war there were lots of M20s present!

BSA M20 riders were trained in bulk during World War II.
British BSA M20 riders were trained in bulk during World War II. Considering the lack of mechanical experience for most Brits, the M20's simplicity proved beneficial.
The final item in the recipe was the M20’s ease of use. Again, it is important to remember how unfamiliar most of the British population was with anything mechanical in 1939. Fridges were rare, washing machines unheard of and many working class people had never even been in a car let alone driven one.

The M20 was low, slow, and almost impossible to stall and therefore ideal for the sort of mass induction programs which were necessary to get tens of thousands of new recruits competent in a very short time.

Not that the M20 was without its faults. The clutch was crude and unreliable and had to be kept free of oil to be working effectively. Some Despatch riders complained bitterly that the clutch on their brand-new M20s dragged and slipped and had to be re-built even before entering service.

In fact, the Don Rs, as they were known, became notorious for customizing their “own” bikes. Ten cigarettes slipped to one of the REME (Royal Electrical and Mechanical Engineer) fitters would ensure that you got a good magneto from the stores or a sweet gearbox and particular bikes became much loved by their riders.

This affection was well placed and the bikes need to be considered through eyes of those who used them. Once you had got over the problem of an M20 spitting back through the carburetor and setting fire to the bike – this was so common that later military M20s carried a fire extinguisher – the BSA would amble along at 45 mph all day and all night without complaint. At this speed, it would consume around one gallon of anything vaguely combustible every 50 miles. No need for high tech gas – the M20 would burn absolutely anything.

The Lucas magdyno provided separate ignition and lighting - excellent for battlefield reliability.
The Lucas magdyno provided excellent for battlefield reliability.
The Lucas magdyno ignition system was also a blessing. The dynamo charged the battery and provided only a hint of lighting but this was not the issue it might seem since all vehicles operated on highly constrained “blackout” illumination.

The magneto element of the magdyno was completely independent of the dynamo and provided a reliable spark to keep the motor running. Roadside maintenance was simple and the width of the points’ gap in the magneto was set with a piece of cigarette paper. “Fag paper clearance…” became an almost standard measurement.

With something over three gallons of fuel in the tank, the M20 had a good range and if the girder forks and rigid rear end did not exactly provide a magic carpet ride they didn’t break either.

With incoming hostile fire, and your life seriously at risk, road side repairs on sophisticated frames or forks would not be high on your “must do” list.

The low ground clearance was not as great a problem as it might first seem. Often, M20s were loaded to ridiculous extents. Whether carrying Junior Officers, whose rank did not warrant the use of a staff car, or ammunition and weapons, the M20 rider needed to be able to instantly place both feet on the ground. Once more, basic engineering was good in battle conditions.

When the bike got stuck it was easy to pull out – on its side or upside down – and then it started instantly. Just as importantly, the docile power, and huge flywheels, meant that M20s would drag themselves out of trouble with the minimum of fuss.

If things got desperate, and death or capture was imminent, a highly stressed M20 could be persuaded to run up to 60 mph – but this was not a sensible or long term, speed.

Valentine Page was charged with creating a 500cc side-valve single with lots of torque for the British military and the BSA M20 is the result.
Dressing for the re-enactment part, a proper Despatch will fetch a correspondingly higher MSRP. The civilian version or lower-spec military model makes for a relatively affordable entry into the vintage motorcycle ranks.
This brings us to the 21st century and M20s. First, however, a digression. There were so many M20s made that tens of thousands of them became available post war. The last ones were sold off when I was a teenager, brand-new and ready to roll, for $45. At the time, all us biking babies sneered at the very thought of riding such a dull, plodding carthorse of a bike – but I still wouldn’t mind 50 brand new M20s, still in their delivery crates, in my workshop by way of a pension plan.

Now, M20s fall into two separate categories. If you want a real, fully equipped, accurate in every detail, military bike for use in re-enactments then M20s are expensive for what they are. However, since you will have already spent a fortune on authentic military id, uniform, weapons and even ration cards, no doubt you can afford the $8000 a correct M20 will fetch.

A less original specimen will be much more affordable – either in quasi-military specification or even the much prettier civilian model. Now, a different set of questions arise. There is nothing overtly wrong with an M20 in that it will start, run, stop and amble round corners satisfactorily but equally, these bikes are desperately dull, joyless things to ride.

M20 enthusiasts will tell you of the bucolic pleasure of cruising English country lanes with the chuff, chuff, chuff of the side-valve engine puffing along beneath you. This is true, but there are so many much better experiences to be had on a summer evening in England. A Tiger 90, Ariel Red Hunter or the Holy Grail of an early Goldstar are vastly better in every way that, other than its purchase price, I can’t think of a reason to ride an M20.
Memorable Motorcycles: BSA M20
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