BSAM20
Will this third BSA side-valve single measure up to the first one? Should you ever go back? Yes, of course you should, if it provides a spark of joy.
I’ve had a soft spot for BSA side valve singles for 25 years. I acquiredmy first one, a 1955 600cc M21, in 1995, from dealer Andy Tiernan. It was extensively rebuilt by Sean Hawker, who formerly ranCMES, the classic electrical specialists. Sean and a friend had ridden their M21s on a 34,000mile trip through southern Russia, into China, down through India and Malaya and all round Australia, so he knew his side valves.
The following year, he and I took a 1500mile roundtrip toamotor showon the Shetland Islands. Sean was riding his expedition bike. Neither of our BSAsmissed a beat.
Peace of mind
When people ask me, or I ask myself, why the obsession and affection for 13 and 15bhpmodels, which where outdated even during their final decade of production, I recall something I’d written about the return leg of that Shetlands journey, riding fromAberdeen down the east coast of Britain on my own:
“A breather pipe came loose, and the clutch got a bit snatchy, but at a steady 55 the engine never smoked or faltered. In the morning rush hour out of Newcastle, or crossing the mile-and-a-half Humber Bridge, or on the empty sweep of a Lincolnshire plateau, I came to realise what wasmissing – any of the usual anxiety about a breakdown, as the M21’s utter reliability brought peace of mind.”
For a mechanical duffer likeme, that was a great gift. And it didn’t come at the price of dullness. The plunger M-Series handling, as someone else observed, features “a wonderful, cobby, sturdy, feel whichmade bends, while not exactly easy, a very satisfying experience.” Fittedwith the 8in sls front brake adopted for the M21 in 1956 and found on other BSAs up to and including the Gold Star, they could stop well too; and after a 12 volt conversion by Sean, the lights were excellent. With a sprung saddle and manual advance/retard to give that ‘one thump every lamp-post’, I used to call it “Edwardian motorcycling with modern benefits.”
I regretted selling that one in 2003, and 11 years later for a keen price, bought a worn-out 1958 M21, with a view to eventually using it as a hack while on a writing stint in France. A friend, Nigel Stennett-Cox, generously set about refurbishing it skilfully and economically (see TCMAugust 2016). But the problems kept coming, and after 15 months and just a few hundred miles, I had to let it go, and took my A10 to France instead. Partly because, whatever was done, this M21 had never gone as well as the first one. This was a TTmodel: Terminally Tired.
New contender
But nourished by a fatal habit of returning obsessively to Tiernan’s ‘andybuysbikes’ website, I still kept an
eye on side valve single possibilities. And sure enough, this 1955 500cc M20 appeared there inmid-2019. Reimported from Denmark and nowwith UK paperwork and an age-related registration, Andy’s no-nonsense description was “old wheezer”, and though it looked pretty much all there in the photos (I failed to notice the missing toolbox!), and was given a fairly positive report and road test (a useful feature of Andy’s sales presentation), the price seemed a bit high at around £4000.
Anyway I’d always told myself, after testing too many tiredWM20s, to hold out for a 600cc M21. Yet recently I’d ridden a really well fettled, early 1940 example – you’ll read about it shortly in TCM– which had modified my view. As the months passed and the M20 seemed nailed to Andy’s floor, I noted that the engine and frame numbers, which on BSAs then were not identical, were still both appropriate to 1955.
As a long-time member of the excellent BSA Owners’ Club – always join a club, you know it makes sense – I wrote to Julian Snook, who had been assisting the club’s over-worked librarian andmachine dating officer, Steve Foden. As requested, I included Andy’s photos of the engine and frame numbers, since “I have seen quite a few,” wrote the helpful Julian, “when the numbers on the V5C are not the same, or not quite the same, as the numbers stamped on the bike.” He then confirmed that the numbers were a factory-matched pair, and that this 1955 M20 had been dispatched onDecember 2, 1954, so was a 1955 season machine. Themodel year had begun in October 1954, with an engine number about 50 before this one.
Tiernan had been told that the M20 might have been ex-Danish Army, but Julian could only confirm that it had been dispatched, one of 19 plungerM20s, to the Danish importer H.V. Hansen Motors and Cycles,
Copenhagen, and that the recordmade no mention of the military. A further 20 rigid-framedM20s had gone to Denmark over the same period. “Did these 39 bikes all go to the Danish Army?” Julian asked “I don’t know, and BSA does not explain!” We would later find under the black paint on the tank traces of maroon, part of the 1955 civilian colour scheme, so the export plunger machines probably had not been destined for the armed forces.
M20s were no longer offered for sale to the public in the UK after the 1955 season. The side valve 500cc single was relatively slow and thirsty, with a 64mph top speed on test and averagempg of just over 50. The ohv B31 350 was 10mph faster, with fuel consumption over 75mpg. Ten years on, any lingering admiration for the M20’s wartime dependability had largely dissipated, and the torquier M21 was preferred for pulling a sidecar. But interestingly Julian confirmed that fleet orders, mainly from abroad, to Shell Petroleum, the Arab Legion, Iranian Oil, and the Milk Marketing Board, meant that the last M20 machines had not left Small Heath until July 1956, and that engines only were being despatched well into 1957.
Andy’s golden axe
I was still scoping the blackM20 in December 2019, egged on by another addict, Len Page on the Isle of Wight (see TCMJune 2018 for the test of hisWM20).
I’d already rung Andy to see if he’d drop the price a bit, but he was adamant. Until December, when he applied Andy’s golden axe to the BSA, cutting the price by £500. Coincidentally I was visiting friends in Suffolk just before Christmas, and arranged to drop over to Andy’s for a test ride.
Mechanic Peter Ransom, who had carried out the test and report for Andy, got the bike ready, while
confirming that the charging problem he’d found had been dealt with. The bike looked tidy and Pete started it first kick. I headed out of Framlingham on country roads. Apart from the front end sometimes feeling slightly uncertain, which I put down to the nonstandardWestern bars, the handling and roadholding on old-style K70 and Avon SM tyres was reassuring. The big front brake didn’t work as well as it should have, and the engine was rattly, but pulledwell. Recorded speeds seemed distinctly encouraging, until I realised that the speedo on this export machine was in kilometres!
After covering eight to 10miles, I returned to Tiernan’s, and at first was unable to shut down, as the handlebar-mounted exhaust valve lifter lever and cable had gone AWOL. After admiring the engine’s steady, unstoppable tickover, I reached down and pulled in the lever on the timing-side case where the cable would have been attached, and the motor futt-ed to silence. After waitingaminute I reset the handlebar advance/ retard lever, and had a go at restarting; sadly for me now, kicking over even a 4.9:1 cr engine is not a foregone conclusion. But happily it fired up third kick. I told Andy that if he’d fit a sidestand, we had a deal. So with the usual mixture of dread and elation, I’d bought my third BSA side valve.
M-Series mafia
Len Page had agreed to fettle theM20. He has two of his own (see TCMFebruary 2020 for his 1944 RN model) plus an M21 outfit. He rode mine away from the lock-up for a service, leaving his girder-forked 1946 model there. He too liked the Danish bike’s handling, but was worried by the sound of the engine. He had the top end off and tested for play in the big end, but there was none. The piston however, had been left very loose in the barrel after a rebore. The alloy head fitted from 1951 tended to amplify noise, while the tank was found to lack the proper rubber mountings, contributing to the rattles.
Meanwhile there was the usual long shopping list of necessary bits, though Len fromhis own spares provided the exhaust valve lifter lever and cable, and a pukka lifting handle to make getting the bike on its centrestand easier. Along with foam grips and a fuel filter, I’d provided a bulb horn, but Len generously gave me a derelict Altette which I could get rebuilt later. On Facebook I read that Sean Hawker was putting his old M21 motor back in its frame, which for years had housed a tuned B31 engine. I got in touch and we’ll meet up before long.
I had experienced some starting trouble on cold mornings, as the separate-float Amal 276 had no choke internals; Len found that it was also set up oddly, and the sooty spark plug indicated very rich running. In the spirit of ‘in for a pound’, via trusted BSA specialists Kidderminster Motorcycles (Tel: 01562 66679), I ordered a new, unleaded-resistant, correctly-jetted Amal 376 Monobloc, the right carb for 1955 anyway, even if it did cost north of £200. But that alsomeant new cables, and a heat-dissipating spacer to clear the dynamo.
Isle of Wight Ken made the latter for us, fromsteel. Kidderminster provided the necessary two new head bolts on the exhaust side, while Len had the threads for the others heli-coiled, before reassembling with a copper head gasket.
Testing, testing
And so forth. But I had, probably unwisely, booked a photo sessionwith ace snapper Gary Chapman, so that I could write this and tell the world about my latest folly. So Len returned the bike without the new carb fitted as the spacer was still en route, andwith his misgivings