If Britain hadn’t needed thousands of solid, straightforward motorcycles for military service in the Second World War, then the side-valve M20 would most likely have evaporated into history long ago. Instead, their wartime ubiquity means that many still s
If Britain hadn’t needed thousands of solid, straightforward motorcycles for military service in WW2, then the sidevalve M20 would most likely have evaporated into history. Instead, their wartime ubiquity means that many still survive and thrive. Stuart Urquhart rediscovers the art of going nowhere slowly…
Many readers may have experience of M20/M21 models, especially given their abundance and attractive low ownership costs during the mid1960s and 70s. I’m a fan and passed my test on a BSA M20 purchased by my dad for the princely sum of specifically for this purpose. It served me well as a stude never once did it let me down on the weekend flight fro to Loch Fyne to admire my girlfriend pulling pints at the Inn. Good times, fab bike.
Harking back to the bike’s beginnings, 1936 was nota for many reasons; the Berlin Olympics, the British mona game of musical chairs, the first regular television servic and it was also the year when BSA’s chief engineer Val designed the sidevalve M20 500. Originally intended as sidecar tug (along with its larger 600cc M21 sibling), the M20 was destined to become the darling workhorse of the forces, with over 126,000 going to the war effort – almost double the number supplied by any other Britis motorcycle manufacturer.
At the outbreak of WW2, BSA was Britain’s largest motorcycle manufacturer, as well as being a major munitions supplier with several rewarding military contracts. But in 1936 when BSA submitted their M20 fo War Office evaluation it was rejected as being overweig and underpowered, as well as suffering from limited gro clearance – characteristics not ideal for combat conditio However, one year later the War Office reconsidered the and the M20 slipped through.
Although it was slow and overweight, the M20’s depe qualities soon won favour with despatch riders and esc personnel. Straightforward to maintain, the simple side technology made the engine virtually unbreakable and sort in the field. However, with girder forks and a rigid frame, these machines were not as comfortable or agile as the Matchless G3L which had Teledraulic (telescopic) front forks and a frame derived from off-road competition.
Countless M20 motorcycles joined the D-Day landings in Normandy – it was by far the most common WW2 military motorcycle and as a result many have survived, both in military and civilian form. Although production of the M20 ceased in 1955 many remained in military service as late as 1965, before being discontinued in favour of the overhead valve, lighter and more agile BSA B40. At the end of the war, many WD M20 machines were simply painted black and snapped up by a transport-hungry public. The 600cc M21 was produced until 1963 with many yellow-liveried AA combinations in service until 1968. The AA M21 became a familiar and reassuring presence for the motoring public throughout the UK.
BSA’s WD M20 was normally covered in khaki green paint with regimental insignia on the petrol tank, and serial numbers painted
white on the mudguards, oil tank and tool box. According to their theatre of war, some army M20s were also painted in sand or camouflage colour schemes. Air Force machines tended to be painted military blue.
The most distinguishing features of a military-spec machine were BSA’s heavyweight girder forks with blackout masked headlamp, rigid rear frame (the plunger frame was introduced postwar), spiked field propstand (located on the nearside), front fork and rear frame mounted pannier frames with fold up trays and canvas bags, canvas handlebar grips, exposed metal ribbed footrests and kickstart. As rubber was scarce during the war years, this machine’s knee-grips are a later addition. Africa desert models had a cut-away section on the offside of the petrol tank to facilitate fitting a large air filter which could cope in hot, dusty conditions.
Its simplicity and indestructibility meant that the M20 was in military and commercial use all across the globe. Weighing 370lb and displacing 496cc, with a bore and stroke of 82 x 94mm, power output was a lowly 13bhp at 4200rpm. Compression was also very low at 4.9:1 – just about good enough for 60mph, and the odd ankle-breaking kickback! The M20 can hold its modest top speed without complaint – another asset of simple sidevalve technology and massive flywheels. Fuel consumption for a single-cylinder motorcycle was pretty poor at around 40mpg. However with plenty of low-down torque and a strong rigid frame, the M20 proved to be a flexible and forgiving motorcycle that excelled in testing military conditions, despite its drawbacks of low ground clearance and a portly build.
The 500cc sidevalve engine runs very hot and is known to burn out exhaust valves – symptoms can include poor starting and erratic running. Running the ignition retarded for long periods can also burn out valves, and the manual advance and retard should be checked regularly along with the ignition timing itself. Popping and banging through the exhaust are early signs of valve wear. Excessive spitting through the carb can be the result of fuel boiling, and fitting a thick and insulating Tufnel gasket between the carburettor and cylinder head is advisable. The valve lifter clearance should also be checked periodically – if it is not sealing correctly this is another sure way to burn out an exhaust valve. Similarly, tappets should be checked according to the manual’s recommended settings to keep the engine running well.
Hereabouts is a richly patinated and decently original WD M20 which belongs to my friend and avid collector of WW2 militia, Fraser. Fraser has owned some very tasty weaponry (all legal of course), and more recently an American Willys jeep, as well as a British Army Armstrong 500. He bought this M20 from dealer and military specialist Stuart Bray, and was attracted by its ‘as found’ condition.
‘I’ve always been interested in vehicles built for a specific military purpose – machines that are reliable in the field as well as being aesthetically pleasing,’ said Fraser. ‘I was drawn to this particular M20 on Stuart’s website because out of the five military motorcycles he was offering for sale, this was the only one that had not been restored.’
Fraser admits that he paid the going rate for his M20, because it came with an authenticated guarantee that it was an ex- WD motorcycle. It had also been serviced and prepared by Stuart. ‘But I had to laugh when I was warned not to use the M20 until I had changed its original WD tyres. WDbranded tyres are a rare commodity on any military machine, and I fully intended to leave them on the bike. But unfortunately I had to replace the front tyre because it was literally falling from its rim, whereas the rear boot was fine – and good for at least another several thousand miles!’ laughed Fraser.
Although it was reregistered in 1968, paperwork confirms that the BSA is a 1943 model. The original 1960s number is faintly visible on the nearside front number plate. During the 60s, military departments offloaded unwanted WD stock through public auctions or direct to dealers up and down the country. Fraser also has documents confirming his M20’s taxation class as ‘unlicensed’ – meaning off-road or military use according to Fraser. Other original WD features abound, such as the brass registration plates riveted inside the toolbox and fading regimental numbers stencilled across many cycle parts.
‘When my M20 arrived I was pleased to have paperwork that endorsed its original condition and low mileage – but with mileage I appreciate it’s anyone’s guess as to how much unrecorded use the bike underwent in service. I need to do some research, as it would be fascinating to learn where the BSA was stationed during its military career.
‘Cables, levers, wiring, WD plates and even the studs, nuts and bolts appear original and
undisturbed. Of course, everything is covered in a thick coat of green. The cycle appears to have two or three layers of paint and that’s one reason I need to research its history. The regimental serial numbers that are stencilled on some cycle parts motivated me into gently rubbing away the top layer of the petrol tank’s paint with wet and dry and I was thrilled when coloured army insignia began to appear.
‘I know from the M20’s paperwork that at one time she was stationed with the Royal Artillery, and I’m hoping that the serial numbers and blue and red colours will eventually authenticate this. A conundrum is the lion emblem that I uncovered topside on the petrol tank which may confuse ties to the Royal Artillery, but as the bike has been painted several times, anything is possible. If any readers have theories as to the origin of the regimental colours I would like to know more.
‘When I replaced the front tyre I was surprised that even the inner tubes were WD stamped. They were faded orange rubber and grossly oversized for the job, in my opinion, and might have better suited a JCB!’ he laughed.
Following delivery Fraser was understandably nervous about starting his M20 for the first time. ‘I took several long breaths and a stiff whisky before I had the nerve to fire her up. I put on my thickest ankle boots and flooded the carb expecting the engine to backfire, but she started first kick and every cat and pigeon for miles fled the din and billowing cloud of smoke – a common result of being wet-sumped. Then my wife opened our bedroom window and berated me for the blue and stinking oil cloud that was about to envelop her washing!’
But Fraser’s first run aroon the block proved to be an unforgettable experience, and he remembers well the ‘nice smell’ as his M20 cooled down in his garage.
Paperwork confirmed that the magneto had been rewound – always a boon with any old classic. The Amal pre-Monobloc carburettor also looked fresh and was certainly spotless inside when Fraser had to remove and clean it during a bout of poorstarting. This is his second M20; his previous one was a moody starter too. Unfortunately M20s are known for running hot, frequently proving difficult to restart following a long run. It is imperative to fit an insulating gasket between the carburettor and the cylinder head flange, and I did note that Fraser’s M20 has one fitted – but I would fit a thicker one. Fraser confirmed that cold starting is usually a one kick affair but, as everyone has their own technique for starting singles, we’ll explore this later during the road test. It is fairly common for M20 models to have broken and corroded cylinder cooling fins – luckily this model’s are intact and in excellent order, if a little rusty.
Fraser’s M20 gets much use and frequently enjoys club runs with the Scottish Classic MC. ‘I like to use the M20 as much as possible, as it’s a thoroughly delightful and uncomplicated motorcycle that has never let me down. Engine, points and carburetion are all good, as are the original chain and sprockets. However the clutch began to slip with prolonged use and I removed the primary casing one day to strip and clean the clutch. The smell of fifty-odd years of decaying lube was amazing – it was like being in an old barn!
‘I also greased the wheel hubs but was a bit over-zealous when I fitted a Willys Jeep grease nipple in order to use my mechanical powered grease gun. It’s a powerful tool that will force out stinky WD grease from hubs and bearings, and transport you back to the Spitfire and glory days!’
As we chatted and photographed Fraser’s much admired M20, he summed up with a few witty comments about ownership and riding. ‘Apart from the odd fettle it’s been all scenery and smiles. The M20 is faster than I had expected and would sit all day long at 60mph if asked, but 55mph is just perfect and in keeping with its archaic push-up valves. “Is Mr Tappet asleep today?” I often imagine the camshaft is asking of the follower.
‘I often tell inquisitive bystanders that it’s a bit like riding a worn-out old bed. Much as you would expect from the 1950s squareprofile tyres, handling is good until you find me lying in the ditch! The gearbox likes to have a lie-in most mornings but is absolutely fine in the afternoons, if not rushed into decisions. It’s a bike for daydreamers and Sunday afternoon strolls. The three and a
half foot jump from third into fourth is mindboggling and when the power comes back in it’s a bit like releasing a giant, wound up, elastic band.
‘Brakes – where are they, pray tell? The back anchor is fine when sitting stationery, but otherwise forget it. Front brake has long been AWoL, and one day I’ll get around to having a peek inside the drum, just to see if anything’s inside... but who honestly needs brakes on a side valve?’ Fraser laughed.
Comedy hour over, it was time for Fraser to have a whirl on my ‘Indian superbike’ (his description of my Enfield Bullet), and in turn I was looking forward to my first trundle on a BSA M20 in almost forty years...
When tripping over the odd bomb crater or hidden foxhole that attempted to impede our progress in snapping pics in and around some local forest tracks, I was genuinely surprised at how easy we found manoeuvring the M20 into the perfect position for my fixed lens camera. The BSA’s elongated propstand also performed as an indispensable crutch for taking time-outs in rough ground while we set up detail shots. With Fraser at the bars and me pushing the rear via its handy panniers, we could shove the bike over exposed tree roots, submerged boulders and up and down ditch and dale – and virtually anywhere with little effort for two men. Useful manoeuvrability I could well imagine for dispatch riders trudging around war-torn France.
When admiring Fraser’s P&J in its familiar surroundings, I could well appreciate the appeal of a non-restored motorcycle. Especially as his rare M20 is oozing originality and looks resplendent in its military guise. The absence of chrome and the well-worn coat of patina that shrouds this old war veteran are hard to find nowadays, and I can understand why Fraser is so engrossed in preserving its history. Charisma just pours from every painted-over nut and bolt. Granted the WD look is olde worlde, but it’s cool and suave enough for wannabe Steve McQueens too. Khaki and canvas suit this old warhorse in a similar fashion to the red and carbonfibre chic of the Ducati Panigale – both are icons of their time.
So how difficult can it be to start an M20? Simply by tickling the pre-Monobloc and selecting half-advance with no need for any choke, it was a first kick affair from cold. But we’ll see how well I perform when the plug is hot. Fraser had warned me about the M20’s poor brakes, so I wore my stout Hoggs Fife boots for the road test. The one digit clutch is a delight and marginally better than my Commando’s – but selecting first gear had bystanders’ heads ducking in expectance of an incoming artillery bombardment.
With first gear engaged, and gently
opening up the light-feeling throttle, we gracefully ambled down the road like there were tomorrows in abundance. By 20mph the revving sidevalve engine was screaming ‘third’ and on the third tomorrow we passed 40mph and into top gear. I’m not alluding to the fact that this bike is ponderously slow; more that there is absolutely no hurry on an M20. The box selects gears quietly and seamlessly provided you take things SLOW. There was no crunching of gears (after first) and not once did I find a false neutral lurking anywhere inside this well-behaved box. Did I mention the light clutch and throttle? Timing the changes with a blip of the throttle also helps to keep everything shipshape and dandy, as this old girl likes to be coaxed along.
Bumbling along the hedgerows, you soon become aware of the lovely muted exhaust that has knowingly seduced you down to a soporific pace, making progress even more pleasant. This, make no mistake, is one green and pleasant motorcycle. Even the metronomic tickover from the engine has the pilot spellbound.
Eventually the rolling war museum and I made progress until I could no longer feel the slim canvas grips. My hands had become gripped with cramp as pins and needles fluttered through my fatigued palms, forcing me to release the bars. I headed for the verge as Fraser had forewarned, but fortunately I had come prepared with my Hoggs and we foot-dragged to a stop courtesy of Fife’s best rubber soles.
‘ Time for the hot-start test’, I bellowed at Fraser as he shot past on India’s superbike looking decidedly bewildered. Four to five frustrated kicks later and we were back in the lazy bangs zone with Fraser forming up the rear in perfect formation.
Then the hypnotic dance of the girder forks takes over before a series of hairpin bends jolts you awake as you fall off the edge of the square profile tyres. But the fright of crashing through potholes on a girder/rigid motorcycle on WD rubbers (the front is an Ensign) will bring any well intended sortie to a grinding halt. This machine gave a new meaning to ‘rear shocks’ and I soon learned to avoid even the slightest road ripple. If you avoid the pitfalls however, the handling is fine and predictable.
I adored the engine’s mellow power and I loved the solid and dependable ride that the M20 could deliver on a smooth road. I would die of fused organs over any rough surface however, and I have formed a new respect for my old man and his boy’s own club of
DRs. That said, the M20 is an excellent plodder and the single, sprung saddle offers a reasonable degree of comfort. Controls are excellent and well-placed allowing the rider to adopt the classic and effortless gentleman’s armchair poise. Once you’ve sorted out the vagaries of the advance and ‘retired’ control lever, and mastered the starting technique hot or cold, you’ll begin to really appreciate life in the slow lane.
Best of all is you can’t go fas won’t even try. Instead you su all the wonderful scenery, exp back roads and contemplate of yesterday motorcycling. No worth slowing down for.
Any machine intended for use off-road needs to be able to stand on its own two stands. This surely is one of the best propstands of all time
Above & below: The front end is heavyweight, intended to survive little maintenance and great abuse, so the forks are robust rather than precise, and hanging bags of tools from the legs of the girders doesn’t help. Forks links are cheap steel...
A neat flashback to the days when ‘green’ meant a colour. BSA plainly had shares in a company making primary chaincase screws, making battlefield clutch adjustment something of a worrisome process
Matters electrical are handled by the ubiquitous Lucas Magdyno, which can be very reliable, even after all this time
Left & right: Two views of a war hero. The M20 engine was intended to be stolid and reliable, capable of being maintained for years in a war zone. Many of them were used by the AA and commuters, too Below: Military history
Before it became a working warhorse, the M20 was intended to be a part of BSA’s civilian line-up and was typical of an affordable tourer. 13bhp was considered ‘ample power for medium sidecar work,’ in the mid-1930s
The hefty 500cc sidevalve single is an easy starter when cold – rather less so when hot. This must have been interesting in the heat of battle