Sunbeam s7 De Luxe
A balloon-tyred tandem-twin the “world’s most magnificent motor cycle”? We go check
'It was a pleasant surprise to find myself astride a goodlooking, sweet-running Sunbeam that was remarkably smooth and comfortable, handled very acceptably, and performed well enough to make for a very enjoyable ride'
CLASSIC BIKES TEND TO provide surprises when you ride them for the first time, which is often not a good thing. Famous old models frequently fail to live up to expectations, either due to problems with an individual machine or simply due to the passing of time. But just occasionally the opposite is true: you come across an old bike that is much better and more fun to ride than its reputation would suggest.
Sunbeam’s S7 has a reputation, all right — and not a good one. This was the balloon-tyred tandem twin, launched in 1947, that was advertised by parent company BSA as the “world’s most magnificent motor cycle”, but which failed dismally to live up to its billing. Words frequently used to describe the early S7 (though not by the uncritical UK magazines at the time) are: unreliable, slow, heavy, ill-handling, under-braked, thirsty, and expensive. Sunbeam never recovered from the model’s poor sales performance and ceased production less than 10 years after its launch.
So it was a pleasant surprise to find myself astride a good-looking, sweet-running Sunbeam that was remarkably smooth and comfortable, handled very acceptably, and performed well enough to make for a very enjoyable ride. Cruising lazily along on the handsome pale-green twin, enjoying its armchair-like ride, I couldn’t help wondering: if an S7 can feel this good so long after being built, can it really have been quite so awful when new all those years ago?
Part of the reason for this bike’s good behaviour was that it was a nicely restored example of the S7 De Luxe, the revised model that was introduced in 1949. This improved on the original S7 with a modified engine and new front suspension, so was more reliable and handled better than its predecessor. But, perhaps, it’s also true that the Sunbeam twin had always been an enjoyable machine, so long as its rider wasn’t in a hurry, and provided the bike was running as it was supposed to.
The S7’s early years were certainly troubled. The model’s story began when the giant BSA group bought Sunbeam from AMC (owners of the AJS and Matchless marques) in 1943. The attraction of Sunbeam Cycles for BSA was the firm’s bicycle manufacturing ability, rather than Sunbeam motorcycles’ reputation for high-quality finish and TTwinning performance, which dated from the original Wolverhamptonbased marque’s glory days in the 1920s. But BSA and Sunbeam boss James Leek was keen to produce a flagship motorcycle, which suited Sunbeam’s upmarket image.
BSA was in possession of some BMW R75 sidecar outfits, captured during World War II, whose proven design looked promising as the basis for such a machine. This plan did not extend to the flat-twin engine layout, which would have been too BMW-like, especially just after the War. Instead, the firm turned to Erling Poppe, a designer of Norwegian extraction. Poppe’s creation combined an R75-based chassis layout with the novelty of a 487-cc, all-aluminium, overheadcamshaft tandem twin powerplant which, like the BMW, used shaft final drive.
Poppe had experience of car and lorry engine design, as well as motorcycles, and his work for the Sunbeam was an attempt to bring four-wheeled attributes such as comfort, smoothness, quietness, and
convenience to the two-wheeled world. But he did not ignore performance, and the S7 prototype that was first tested in 1946 had lively acceleration and a top speed of 150 km/h.
Unfortunately, BSA’s testers soon realised that not only did the prototype engine vibrate badly — it was, after all, a solidly mounted parallel twin, albeit turned at 90 degrees from the normal layout — but it was also unreliable. It had insufficient oil capacity, and its drive shaft turned the rear wheel not via a conventional bevel drive, but by a “worm” drive inside the rear hub — a setup that wore very quickly.
Equally seriously, the prototype S7 combined fat, 16-inch tyres with an unusual form of telescopic front suspension, designed by Poppe. The main legs contained no springs. Shock-absorption was by a main spring, plus smaller rebound spring, placed centrally between the two legs, running down from the steering head to the front mudguard. Steering was vague and got worse when the throttle was opened or closed suddenly — when torque-reaction sent the bike to the right, reportedly so fiercely that BSA’s test-riders occasionally ran off the road in left-hand bends.
BSA’s response was not to completely redesign the bike, but simply to detune the motor, rubber mount it, and tip it back in the frame by three degrees to reduce torque reaction. This did the trick as far as vibration and torque reaction were concerned, but the other flaws were not so easily cured. And the detuned engine, whose new cylinder-head had all four valves on the right side, with a smaller carburettor moved across to sit between the twin exhaust ports, produced a maximum of only 25 PS at 5,800 rpm.
This reduced the production S7’s top speed to a modest 120 km/h and also cut the acceleration of a bike which, at almost 200 kg dry, was no lightweight. Worse still, even this detuned motor proved very unreliable, with a list of problems that included overheating (mainly due to the limited oil capacity), cracked cylinder liners, fast-wearing rubber mounts, and weak valvegear. Perhaps, it’s no surprise that by the time the bike was in production, in 1947, designer Poppe had been fired and given 15 minutes to clear his desk.
But for Sunbeam and parent company BSA, there was no alternative but to press on with the S7. One of Poppe’s successes had been to create a distinctive and stylish machine whose tyres, big fenders and sprung saddle owed much to Indians and Harleys. But even this look was of dubious advantage, because in Europe those American bikes had a reputation for poor handling. The result was that in the first two years Sunbeam sold only 2,000 units of the S7, a disastrous return on BSA’s investment.
The fightback began in spring 1949, when Sunbeam introduced two derivatives: the lighter, cheaper and more conventional S8, and the S7 De Luxe. The latter had a revised engine with a deeper oil sump, new cylinder liners and larger rubber mounts. Its chassis also received a much-needed upgrade, most importantly gaining conventional front forks with internal springs and hydraulic damping.
Styling was unchanged, and one glance at this very nicely restored 1949-model De Luxe made that decision easy to understand. The S7 had always been a handsome machine with a clean, integrated look. My first surprise was that despite those big tyres and fenders it was
quite small and compact. The saddle was very low, and the bike felt notably light and manoeuvrable as I fired the softly tuned engine into life with a gentle swing of the kick-starter.
That easy starting ritual was reflected in the whole of the bike, I soon discovered, after accelerating away to confirm for myself those stories about the Sunbeam’s modest engine performance. True enough, the acceleration was nothing to get excited about. But its low-rev judders soon faded and the S7 could be revved quite hard without generating annoying vibration. It was also pleasantly torquey and responsive at medium engine speeds.
This bike also benefited from a light clutch (a car-type single-plate design had also been revised in 1949), and a sweet-shifting four-speed gearbox. There was plenty of power for cruising with 80 km/h or more showing on the optimistically provided 120 mph (193 km/h) Smith’s speedo, with acceleration in hand for overtaking. And the S7 also gave the bonus of an unexpectedly rorty note from its two-into-one exhaust system, especially when I changed into top at about 70 km/h and the sound deepened to an improbably sporty brrrrapp.
Handling was not as bad as I’d expected, either, presumably due largely to the benefits of the new forks. These had no compression damping and only very basic hydraulic rebound damping, so the ride was slightly choppy, as was that provided by the rear end’s plunger setup. The spring-loaded saddle’s gentle bouncing added to the vague cornering feel, too, and those big balloon tyres doubtless contributed to the slow steering.
But the S7 frame was a rigid twin-downtube structure of chrome molybdenum tubing, which helped keep the bike stable at speed. And despite the bike’s slightly loose feel, it could be cornered enthusiastically enough to touch down the centre-stand. The S7 De Luxe was by no means a sporty bike, and its single-leading-shoe front brake needed a firm squeeze of the lever to have much effect. But the chassis behaved well enough to make for an entertaining ride.
Sadly for Sunbeam, neither the De Luxe nor the lighter and sportier S8 model, also launched in spring 1949, could turn around the company’s fortunes. Sales did improve, with the S8 being the more popular model. By the end of 1952 more than 10,000 of the twins had been produced. But from then on, Sunbeam went into decline. Development of the S7 and S8 models came almost to a halt. And a promising S10 prototype, which combined a more powerful 600-cc engine with conventional shaft final drive, was never produced.
The end for Sunbeam came in late 1956, when the firm came under the control of BSA’s boss Jack Sangster and his right-hand man, Edward Turner, who moved swiftly to stop production. Apart from a final insult when BSA used the famous Sunbeam name on a couple of scooters, another of the great old British marques had gone. But it only takes one ride on a sweet-running old S7 De Luxe like this one to confirm that, despite its poor reputation and commercial failure, Sunbeam’s flawed twin had much to offer as a stylish, comfortable roadster.
When was the last time you saw a tandem-twin layout?
Note how the reading begins at one o'clock
The drive shaft is connected to a worm drive inside the rear hub