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


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