Norton’s first 750cc twin, reluctantly designed for the power-hungry Americans, shook at speed, but, today, its many virtues make it a highly desirable classic.
Words: STEVE WILSON Photographs: GARY CHAPMAN
I first saw and heard a Norton Atlas on the stage of Her Majesty’s Theatre in London’s Haymarket, in 1961.
‘Bye Bye Birdie’ was a loose take on an Elvis-figure in a small Ohio town, about to enter the US Army. As a teen musical it wasn’t a patch on ‘West Side Story’, which I’d also seen previously at Her Majesty’s. But rock star ‘Birdie’ did roar in on a high-handlebar Norton Atlas, a model just released for the US market’s 1962 model year. So cool.
Atlas in classical mythology had been strong enough to hold the world on his shoulders, but the Norton name more likely drawn from the 1957-on rocket, America’s first intercontinental ballistic missile. Both the missile name and the musical presence indicated that this Norton had been aimed squarely at the USA.
The Atlas story
The 750cc twin had been developed by Doug Hele at Bracebridge Street, before he left to join the Norton twin’s original designer, Bert Hopwood, at Triumph. Norton’s Plumstead-based parent AMC company was already in financial decline, and, having made a mess of their wholly-owned US export operation, appreciated their current US importers, the Berliner brothers’, willingness to pay for machines as they left the production line. But that, along with the rapid contraction of the UK motorcycle market, meant that the Berliners’ tail now wagged the Plumstead dog. And what Joe Berliner wanted was a big, powerful but flexible engine, capable of doing 20 to 100mph in top gear.
Hele had overseen the successful export Manxman 650 for 1961. However, despite sharing the latter’s Slimline Featherbed frame, Roadholder forks, magneto ignition, and even the ratios in its excellent AMC four-speed separate gearbox, Hele had severe reservations about the vibration that came with the move up to 750cc for a parallel twin. He later told author Mick Duckworth that “Fred Swift, one of our test riders, came back from a high-speed (pre-production) run on the M1 motorway, and his hands were swollen. I decided that if we put a big twin into production, it should not have a compression ratio higher than 7.5:1.”
There were other problems. There was not enough room between the cylinders as currently arranged to simply bore them out from the 650’s 68mm (x 89) to 73mm. So Hele had to move the block back some 0.01 inch to provide room; creating a désaxé arrangement, as it’s called, when the cylinders are offset relative to the crankshaft. The cylinder base holding-down nuts were thus different to the 650’s. Another distinguishing feature from the 650 was that with the new layout, the crankcase breather outlet moved to the drive side.
Initially a single carb was intended, to further restrict power, but in production twin 11/16 inch Monoblocs were fitted, with a single float chamber on the left-side instrument. This was to keep width down, because Norton’s fine-breathing cylinder head featured parallel inlet ports, with inlet valves close together, so that the mixture came into the combustion chamber tangentially, promoting swirl in the hemispherical heads to aid combustion. By contrast the exhaust ports and their valves were widely separated, making for a good flow of cooling air down the middle of the head.
The 1962 export-only Atlas went out with 7.6:1 compression and a claimed 49bhp, the same as the 650SS, but testers found the big engine notably more flexible. With a chromed primary chaincase, rear chainguard and mudguards, plus the high bars and small (2.5 Imperial gallon) ‘gas’ tank US riders favoured, and soon to be offered in Metallic Ruby red as well as traditional silver and black, the Atlas did not disappoint, offering 0-60mph in 5.1 seconds and an average top speed of 119mph. The Featherbed handling was its peerless self, and a 1963 Cycle World test didn’t even mention vibration!
Back in Blighty, as Bracebridge Street closed and Norton moved in at Plumstead later that year, there had been an early problem, with some frames breaking just above the front engine mounts due to the 750’s grunt. Ken Sprayson at Reynolds, where Featherbed chassis were built, quickly cured this, by inverting the mounting lugs so that their tails were uppermost.
In addition to the Atlas-engined Matchless G15/AJS Model 33 roadsters, the Berliners’ demands led to the 1963-67 Atlas Scrambler, the 1965-67 N15CS/G15CS, and along with other variants, the 1967-69 P11 (“Dynamite On Wheels!”)/P11A/Ranger. All were Atlas-engined, and some 7000 of these ‘Hybrids’ were produced. They’re another story, but they did keep Atlas development going, and their production dates at Plumstead spanned the demise of AMC in Sept 1966, and the creation of Norton-Villiers.
Norton v AMC
The principal ‘experimental technician’ on Atlas development was ex-Comp Shop man Wally Wyatt. Rivalry between Norton and AMC was long-standing, and Wyatt later wrote that the Norton twin’s “cylinder head porting was so bad that I couldn’t even get my finger down it,” and claimed that “with a bit of file work” he was soon getting 59bhp from the Atlas and 67bhp on racing versions.
However, one of the few Bracebridge Street men who had moved to Plumstead, the immensely knowledgeable trouble-shooter John Hudson, knew that Wyatt was getting his results partly by raising compression ratios, and wrote that Wyatt ‘…should never have done it if he had known anything of the designer’s original intentions.’ And writing retrospectively in Classic Bike, Bernard Hooper, co-designer of the Norton 750 Commando, stated unequivocally that “Wyatt had raised Atlas output to 47bhp – forget the published figures.”
Certainly, by August 1965 another Cycle World test on a 7.6:1 c.r export Atlas wrote that “unfortunately the engine also delivers some quite spirited shaking,” though they found it very usable around town due to its low speed pulling power, and qualified the shakes on long fast trips as ‘…not really any worse than any other big displacement twin.’ A retrospective 1974 piece on Norton twins in Cycle, however, concluded that: “The Atlas was an unhappy motorcycle…(it) did not merely vibrate nuts and bolts loose. It quaked down highways seeding the berms with metal.”
Certainly it was an Atlas pillion ride, and the vibes felt through footrests and saddle, that had appalled Dr Stefan Bauer. Bauer, a distinguished scientist, was Norton-Villers’ boss Dennis Poore’s Director of Engineering, and a non-motorcyclist; and after the pillion experience, he insisted that on a proposed new Norton twin, vibration would not be tolerated. And so, thanks to Hooper and Bob Trigg, the Commando with its Isolastic system for the modified Atlas engine, was born in Sept 1967.
Meanwhile, the Atlas in the UK had gone first to the police in all-white livery, and then from February 1964 to the public, finished in classic silver and black, with a later burgundy option for the tank. UK versions featured Norton ‘straight’ handlebars, a 3.2 Imperial gallon tank, 12 volt electrics, and, with the US still in mind, Roadholders widened to take a fatter front tyre. In 1965 the rear chain was also widened to 5/8 x 3/8in. UK testers found the Featherbed handling undiminished, but 4500-5000rpm to be as fast as it would run smoothly. For 1967 the carbs changed to Concentrics.
The 1968 season, with the Commando now the focus, was to be the Atlas’ final year, when it nominally (though not always in practice) featured coil ignition with alternator and capacitor, and from mid-1967, revised oilways and doubled circulation from a modified oil pump. There was also, finally, a rear hump on the dualseat, as early on US testers had found themselves sliding along the smooth seat pushed by the 750’s incredible acceleration! Then the Norton story moved on.
The Druid connection
Dave Owen is no stranger to these pages (see the ISDT-spec Ariel KH twin, TCM July 2022), but so far mainly featuring his Ariels, the marque he has concentrated on since 2000. But before that, since the mid-1970s, from the Dominator 88 he owned when he took his test, to the brand-new Commando 850 Mk3 on which he covered 25,000 miles in two years, or more recently, an ex-WD 16H outfit, or a 1972 Kuhn 750 Commando (“A real flyer!”) – it was Nortons.
He bought the Atlas in 2021 from the estate of the late Terry Dobney. Terry was a former soldier, a motorcycle engineer, a specialist in Indian motocycles, and, famously, an Archdruid, which he took seriously, and Keeper of the Stones at Avebury. Dave had to have his Atlas. The Featherbed 750s are relatively rare.
The machine was something of a bitsa, with a 1962 frame and a 1968 engine – even though it still features a magneto (“Not the first time I’ve seen this,” Dave commented). It had first been registered in February 1968, though Atlas production had actually ceased that January, despite being listed for the full model year. “The V5 states ‘rebuilt from parts, not all new’,” said Dave, “so I’m assuming it had been off the road at some time and the registration number reclaimed.
“When I got it, the advance/retard unit was missing, and the magneto needed a full rebuild. Then I checked everything over, replacing all the drive chains and the rear brake shoes. I also changed the leaking head gasket to a solid copper one.” In 1965, the Norton twins’ spigots on top of the cylinder block and their matching recesses had been removed, probably on cost grounds; John Hudson told me that spigotless heads had been thoroughly tested in Bracebridge Street, but the previous arrangement retained as better engineering.
The numbers on the cylinder head indicate that it was a Commando one, of the type developed by Wyatt, giving around 9.0:1 compression. The carbs are twin 32mm Concentrics. “The clutch is quite heavy,” said Dave, “due to my fitting stronger springs to cope with the power; standard Norton springs caused instant clutch slip at speeds over the legal limit.” In the year since he’s had the Atlas, Dave has done around 2000 miles on it.
Masterclass
Riding the Atlas filled in a gap for me, as I’d owned 350cc, 500cc and 650SS Norton twins, plus 750cc and 850cc Commandos, but never the Featherbed 750.
I let Dave do the starting honours which he performed second kick. Climbing aboard was easy despite a catalogued 31.5 inch seat height; this felt like a low-set machine, and with high-mounted footrests for good ground clearance, gave a slightly jockey-like riding position, though less so than its contemporary, the T120 Bonneville. The clutch pull was fairly stiff but not terrible, and the gearchange notchy but clean, with no unwanted neutrals. Both brakes were okay, the eight-inch tls off a Commando nothing special, but the rear seven-inch sls, good.
But all this evaporated on the sunny B-road with its series of curves, both sharp and then progressive, and a humped railway bridge at one end. Suddenly I was back in the land of “on rails”, just think of a line and you’re on it. Featherbed country. I had forgotten how superlative the roadholding had been on my Slimline 650, and I knew from experience that this remained true for both wet and dry roads. This Atlas’ Avon Roadrider tyres didn’t hurt, either.
The nice rorty note from the ‘cigar’ silencers filled my head as it rose and fell. The vibes at these relatively low speeds, up to 60mph, seemed normal. Norton twins, Commando excepted, had rarely been a comfortable ride. Though the ergonomics of the riding position were spot on, the fairly hard springing from the Roadholders and thick Girling units, while contributing to the superb handling, also took its toll on long journeys. Riding the 650 back from Morocco, the trip from Marseille to the Dordogne in one hot afternoon had been pretty harsh, especially for my pillion.
But – I was blissed out, the tilting, swooping ride, with Norton ‘straights’ in place, felt so precise, so right. And on the Atlas, unlike the 650SS which had to be revved purposefully beyond 4000rpm (which I very rarely did) to get on the power–band, the big, responsive, unfussy 750 had scads of poke at virtually any revs. It seemed like the best of both worlds.
Still, I had to explore the downside, those bad vibrations. But as I wheeled around to head for straighter stretches and turn up the wick, the engine died. And would not come to life again. Druidry? No, it later transpired that an insulating washer in the magneto had broken, causing a short. But the ride so far had convinced me that relishing the handling and playing tunes on that wonderfully flexible engine, while keeping to cruising speeds (and do many of us regularly go chasing the ton on our classics these days?), this big Featherbed twin was a thing of beauty and a joy forever.
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