BSA M20

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

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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.

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

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

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 stamp­ings, the brake is ex­cel­lent for slimy mu­dor ice but not much else, and the speedo is mostly aca­demic. All of which adds to the en­ter­tain­ment of the ride

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