SUNBEAM S7 & S8

The gen­tle­man’s mo­tor­cy­cle

Old Bike Australasia - - FRONT PAGE - Story Jim Scaysbrook Photos Ray Goul­ter and Jim Scaysbrook

Ac­cord­ing to def­i­ni­tion, a sunbeam is a del­i­cate shaft of light, and while the term ‘del­i­cate’ may well be ap­plied to the pre-WW2 of­fer­ings from the Wolver­hamp­ton-based com­pany, it is not a de­scrip­tive that springs to mind for the in-line twins that ap­peared post-war fol­low­ing Sunbeam’s takeover by BSA.

In fact, the pre and post-war of­fer­ings were poles apart. On one hand, lithe sport­ing sin­gles pos­sessed of a healthy turn of speed and sub­lime han­dling, and on the other, rather bloated and un­der­pow­ered. Yet the Sunbeam S7 was in in prin­ci­ple at least, ex­actly what the British mo­tor­cy­cle in­dus­try des­per­ately needed to em­brace – fresh think­ing. Sunbeam it­self had a che­quered his­tory, be­gin­ning in 1899 as the prod­uct of John Marston Ltd. The first pow­ered Sunbeam was a strange look­ing four-wheeler with a sin­gle wheel front and rear and wheels at each side – of­ten de­scribed as a ‘sofa on wheels’. Sub­se­quent Sunbeam cars were far more el­e­gant, and this side of the busi­ness was split to be­come the Sunbeam Mo­tor Car Com­pany which pro­duced a line of highly ac­claimed ve­hi­cles. The orig­i­nal con­cern con­tin­ued as a man­u­fac­turer of pedal-pow­ered bi­cy­cles, uniquely fit­ted with a fully en­closed oil bath rear chain – a fea­ture car­ried over to the first Sunbeam mo­tor­cy­cle, the Gen­tle­man’s Mo­tor Bi­cy­cle, which ap­peared in 1912. A 350cc sin­gle with a two-speed coun­ter­shaft gear­box and multi-plate clutch, the new Sunbeam was a qual­ity item, with a rear-mounted Bosch mag­neto and ec­cen­tric fly­wheels to achieve crank­shaft bal­ance. The im­pec­ca­ble fin­ish be­came a sig­na­ture of sub­se­quent Sun­beams, with deep black enamel fin­ish and genuine gold leaf let­ter­ing and lin­ing. Hav­ing sur­vived WW1, Sunbeam was struck a crip­pling blow when John Marston died in 1918 aged 82, fol­lowed less than a year later by his son Roland. The com­pany soon had new own­ers, Noble In­dus­tries, which it­self later be­came the gi­ant Im­pe­rial Chem­i­cal In­dus­tries (ICI). Un­der the new own­er­ship, Sunbeam flour­ished, with com­pe­ti­tion suc­cesses that in­cluded Isle of Man TT vic­to­ries. New 350 and 500cc over­head valve en­gines were im­me­di­ately fruit­ful, and the com­pany re­cruited Graeme Walker (fa­ther of Mur­ray) as Com­pe­ti­tions Man­ager and works rider. Grand Prix and fur­ther TT wins fol­lowed, but so did the De­pres­sion, and the Sunbeam range was trimmed to just four mod­els. Un­like many of its com­peti­tors, Sunbeam saw out the cri­sis, but in 1936 ICI sold Sunbeam to Lon­don-based Match­less, who al­ready owned AJS, to form a new com­pany called As­so­ci­ated Mo­tor Cy­cles Ltd (AMC).

For a year or so, lit­tle changed in the Sunbeam line up, but then came a com­pletely re­designed model, known as the High Cam, which was not in keeping with the svelte and sporty mod­els of the past. Pro­duc­tion of the new line had barely started when Bri­tain once again found it­self at war. Al­most covertly, as the war drifted to­wards its con­clu­sion, AMC qui­etly di­vested it­self of the Sunbeam brand, which now be­came part of BSA in Birmingham in 1943. It could have been ex­pected that BSA, hav­ing ac­quired the tool­ing as well as the nam­ing rights, would sim­ply con­tinue where AMC had left off, but what ap­peared as the next chap­ter in Sunbeam’s his­tory owed noth­ing to what had pre­ceded it. What BSA en­vis­aged was a luxury ma­chine with a com­pletely unique spec­i­fi­ca­tion, and to achieve this BSA hired a de­signer from out­side the main­stream mo­tor­cy­cle in­dus­try; Aus­trian-born Er­ling Poppe, who had pre­vi­ously been a de­signer at the bus-build­ing divi­sion of British Tramways and would later be­come chief de­sign engineer at Rover cars. Ear­lier in his ca­reer, Poppe had been a part­ner in Pack­man & Poppe, pro­duc­ing a 250cc two stroke utility mo­tor­cy­cle and later a 976cc side-valve JAP-en­gined model, but he had been away from the mo­tor­cy­cle scene for more than 20 years when he ar­rived at BSA. Although the BSA board placed sev­eral stip­u­la­tions in re­gard to their new Sunbeam model (in­clud­ing that the per­for­mance should match the Tri­umph twin, and ‘must not in­cor­po­rate BSA fea­tures that could be recog­nised’), Poppe was not given carte blanche when it came to the de­sign of the new 500 twin, which was in fact pro­jected to be the first of a line of sim­i­lar de­signs that would in­clude a 300cc ver­sion. In­stead, Poppe was given the de­sign of a BSA pro­to­type from the ‘thir­ties which had failed to pro­ceed to pro­duc­tion, the Line-Ahead Twin. His stay at BSA was brief, and the fi­nal touches to the new Sunbeam were en­trusted to Gerry Bayliss. Des­ig­nated the S7, pro­to­types of the new model were built in two forms; a tour­ing ver­sion and a sports ver­sion, the lat­ter of which never reached pro­duc­tion. Poppe brought much car-based think­ing to the draw­ing board, seek­ing a clean, smoothrun­ning, quiet and easy-to-start ma­chine. The en­gine it­self, with its unit four-speed gear­box, was an all-al­loy, wet sump par­al­lel twin with the crank­shaft set along the frame and hor­i­zon­tally-split crankcases, with the top half in­cor­po­rat­ing the cylin­der block. Oil was con­tained in a casta­lu­minium sump bolted to the lower face of the crank­case. The first cylin­der head pro­duced was a cross-flow de­sign, with the car­bu­ret­tor on the left. The com­bus­tion cham­bers were of the squish type, and the en­gine, in pro­duc­tion form, was ef­fi­cient and rea­son­ably pow­er­ful. Fi­nal pro­duc­tion heads had the in­let port and car­bu­ret­tor switched to the right side, sit­ting be­tween the ex­haust ports.

The valves were op­er­ated by a chain-driven sin­gle over­head camshaft, and fi­nal drive was by shaft. To re­duce the in­her­ent me­chan­i­cal noise of an all-al­loy

air-cooled en­gine, short, stiff fins were cast, and the camshaft fit­ted with qui­eten­ing ramps to pro­vide a slow tran­si­tion for an 18-thou tap­pet clear­ance. The de­sign team be­lieved that the elim­i­na­tion of pushrods in favour of the over­head camshaft would also lower me­chan­i­cal noise, and also al­low the use of lighter valve springs, which in turn pro­duced less wear on valve seats and fur­ther re­duced noise. The choice of a chain rather than a ver­ti­cal shaft to drive the camshaft was also done for noise rea­sons. The cylin­der head used a sin­gle in­let port with an Amal Type 275 car­bu­ret­tor with a tiny 15/16” choke size, and twin ex­haust ports. A Vokes oil-drip air fil­ter was housed in a swish look­ing shroud, held in place by three acorn nuts. On the op­po­site side of the head, a cast-al­loy stream­lined and finned cover kept the weather away from the spark plugs. At 70mm x 63.5mm, the en­gine was well over­square, and used very short light al­loy bolted-up con­rods to keep pis­ton speed down and en­sure the en­gine was as com­pact as pos­si­ble. Each Y-al­loy pis­ton used four rings; two com­pres­sion rings and an oil ring above the gud­geon pin, and an­other oil ring at the base of the skirt. The one-piece iron crank­shaft had a very large cen­tral bob-weight, sup­ported at the front by a ball bear­ing and at the rear by a plain, white-metal lined bear­ing with a spring-loaded oil seal to pre­vent en­gine oil from reach­ing the clutch. The clutch used a sin­gle seven-inch plate, car-style, op­er­at­ing di­rectly onto the fly­wheel. Ig­ni­tion was by bat­tery and coil, with an au­to­matic ad­vance and a dis­trib­u­tor driven at half en­gine speed from the rear end of the camshaft. Power was sup­plied by a 40-watt Lu­cas dy­namo with the ar­ma­ture car­ried on the front end of the crank­shaft where it re­ceived a di­rect stream of cool­ing air.

The cra­dle frame had widely spaced front tubes that were bolted to the front of the crank­case, with tele­scopic forks at the front and plunger rear sus­pen­sion. Defying con­ven­tional logic and per­haps with a tilt to the US market, fat 4.50 x 16 front and 4.75 x 16 rear tyres were fit­ted. Although con­ven­tional in ap­pear­ance, the front fork was a be­spoke item with no in­ter­nal damp­ing for the legs. In­stead, the tubes con­tained oil-soaked cot­ton for lu­bri­ca­tion with rub­ber bump-stops for the slid­ers. A speedo was lo­cated in the head­lamp to the right hand side, with a pair of warn­ing lights on the left; red for ig­ni­tion and green for oil, the lat­ter blink­ing if the oil level fell below one pint.

The fi­nal drive shaft had univer­sal joints front (a rub­ber Layrub cou­pling) and rear (a Hardy Spicer metal unit) that ran at ap­prox­i­mately half en­gine speed in top gear. How­ever in­stead of the bevel crown wheel and pin­ion used by oth­ers in­clud­ing BMW and Zun­dapp, BSA stip­u­lated the use of worm and wheel drive gears, prob­a­bly be­cause these were a stock item used in an­other BSA prod­uct – Daim­ler cars. This com­po­nent proved to be the Achilles Heel of the en­tire de­sign, although when prop­erly set up with shims and match­ing com­po­nents, plus the cor­rect grade of lu­bri­cant, can give long trou­ble-free ser­vice. By 1945, the pro­to­type S7 was ready for test­ing, but the un­for­tu­nate chaps to whom that task fell re­ported that the vi­bra­tion from the en­gine, which was rigidly mounted in the frame, was so se­vere that it was all-but un­ride­able. Even with this fault, the first batch of S7s was built in 1946 with the en­gines se­cured di­rectly to the frame, but all were re­called for mod­i­fi­ca­tion. In a very em­bar­rass­ing episode for the brand, a small batch of S7s from the first pro­duc­tion run was rushed to South Africa to act as es­cort ve­hi­cles dur­ing the visit of King Ge­orge VI, but the rid­ers com­plained so ve­he­mently of the vi­bra­tion they were with­drawn and sent back to the fac­tory. The fix was in the form of iso­lat­ing the en­gine from the frame by a se­ries of elas­tic mounts. The low-fre­quency vi­bra­tion was ab­sorbed by two di­ag­o­nally-dis­posed, bonded rub­ber en­gine mount­ings. To ab­sorb half-fre­quency vi­bra­tion, caused mainly by the mo­tion of the con-rods, a spring-loaded fric­tion damper was mounted at the top (rear) of the en­gine. What BSA/Sunbeam called “snub­bers” – small rub­ber buf­fers car­ried at the top (rear) and bot­tom (front) of the en­gine – con­trolled os­cil­la­tion. The en­gine still danced around, but at least the ef­fect was no longer trans­ferred to the rider. To pre­vent the ex­haust sys­tem from break­ing up un­der the vi­bra­tion, a short length of flex­i­ble metal­lic tub­ing was used to cou­ple the pipes.

Ini­tially the S7 was avail­able only in black, but a Mist Green op­tion was soon in­tro­duced. When the S7 went on sale in 1947 it car­ried a sub­stan­tial price tag – £222 (In­clud­ing UK pur­chase tax) when the com­pany’s own BSA 500cc A7 twin sold for just £167. As feed­back from ini­tial sales drifted in, a com­mon prob­lem was high­lighted; that the fi­nal drive set up chopped out af­ter as few as 5,000 miles. Un­less metic­u­lously set up, the worm-drive to the rear wheel was in­ca­pable of trans­mit­ting the power of the en­gine, and the gear­box cas­ing also grew ex­tremely hot af­ter a de­cent run, so com­pany’s an­swer was not to re­design the fi­nal drive com­po­nen­try, but to de-tune the en­gine to pro­duce some­thing like 24hp. The un-damped front forks soon gained sin­gle-way damp­ing, which im­proved ride qual­ity con­sid­er­ably, and nu­mer­ous other de­tailed changes made to the S7, such as re­plac­ing the orig­i­nal in­verted front brake and clutch levers (which piv­oted from the ends of the rub­ber-mounted han­dle­bars in true vin­tage style and had their ca­bles run­ning in­side the bars), with con­ven­tional levers and ex­posed ca­bles. A new model, mar­keted as the S7 De Luxe was shown at the first post-war mo­tor­cy­cle show in Eng­land, held at Earls Court, Lon­don in Novem­ber 1948. Also dis­played at this show was a sec­ond ver­sion, called the S8, avail­able in black or poly­chro­matic grey, with a cheaper price and 12kg less weight,

which gave it bet­ter per­for­mance. The S8 dif­fered in many ways, in­clud­ing a re­vised oil­ing sys­tem with a larger ca­pac­ity, but vis­ually the main change was the re­ver­sion to con­ven­tional 19-inch front and 18 inch rear wheels and tyres, nar­rower sec­tion mud­guards and lighter front forks and a smaller front brake sourced from the BSA twin. The S8 also had a con­ven­tional sprung sad­dle in­stead of the Terry can­tilever type on the S7. In place of the S7’s tubu­lar steel si­lencer, a cast alu­minium ver­sion was used. In both the S7 de Luxe and the S8, en­gine power was in­creased slightly to 26hp. The S8 went on sale in 1949 but although the S7 con­tin­ued along­side it un­til pro­duc­tion ceased in late 1956, nei­ther ever sold in ac­cept­able quan­ti­ties, although BSA an­nounced in Novem­ber 1951 that the 10,000th Sunbeam twin had just rolled off the pro­duc­tion line. Six years later, this fig­ure had in­creased by just over 6,000. The of­fi­cial pro­duc­tion fig­ures are 7,658 for the S7 and S7 de Luxe, and 8,530 for the S8. A ma­jor fac­tor in this lack of show­room suc­cess was un­doubt­edly the price, which by 1950 had risen to £259 for the S7 and £227 for the S8, when a 500cc Royal En­field twin went for £177 and the A7 BSA twin for £182. But there was also the mat­ter of styling, which was a ‘love it’ or ‘hate it’ sit­u­a­tion with buy­ers. An­other fac­tor was the rather un­der­whelm­ing per­for­mance, which could only be rec­ti­fied by a com­plete re­design of the trans­mis­sion. Both the S7 and S8 had been built to the high­est stan­dards of fin­ish and ap­point­ment, and BSA felt there was no point in com­pro­mis­ing this by low­er­ing spec­i­fi­ca­tions to achieve a lower re­tail price. And so af­ter a lit­tle more than a decade in pro­duc­tion, one of the most in­no­va­tive post-war British de­signs slipped into obliv­ion. For all its quirks, Sunbeam S7/8 own­ers uni­ver­sally praise the smooth­ness of the rid­ing ex­pe­ri­ence, which is a far cry from the hippy-hippy shake of the first batch. To­day, ex­am­ples of the Sunbeam twin – uni­ver­sally re­ferred to as “The Gen­tle­man’s Mo­tor­cy­cle” since its in­cep­tion – are highly prized, and the long-es­tab­lished Ste­wart Engi­neer­ing in UK does a world­wide trade in new and sec­ond hand S7 and S8 parts.

Thanks here to Bryan Fowler (British born, raised in USA, and for the past decade, a Syd­ney res­i­dent)

for the op­por­tu­nity to pho­to­graph his 1953 S7 De Luxe. Among sev­eral oth­ers, Bryan has three mo­tor­cy­cles that he be­lieves were sig­nif­i­cant turn­ing points in the post-war British mo­tor­cy­cle in­dus­try; the S7, a Ve­lo­cette LE, and an Ariel Leader. I think he is quite cor­rect when he says that this trio em­bod­ied very fresh think­ing – a deliberate move to break away from the tra­di­tional and tired de­signs that had be­come en­trenched in the in­dus­try. His S7 was pur­chased from Kohl’s in Lock­port, New York (see Bryan’s story in OBA 72 Out & About). “I bought it in 1982,” says Bryan, “af­ter look­ing at it sit­ting on the shop floor since 1977. I also re­built one last year that I bought in New­cas­tle, NSW. These bikes have lots of traps for would-be re­stor­ers; left thread axles, hid­den nuts in the cylin­der heads; peo­ple miss these and try to lever heads off. I have had BMWs (and still ride one) but the S7 is one of the smoothest bikes I’ve ever rid­den. This one has the Mk2 front forks, which are much bet­ter. They ab­so­lutely must have metal fuel lines or they melt on the ex­haust pipes and the bike can catch fire. The dip­sticks used to blow out with crank­case pres­sure, so they were re­designed with a se­cur­ing clip. On the early en­gines the cylin­der sleeves were not pinned and tended to work loose, so the later ones were pinned.” With as­sis­tance from his wife Zac, who tol­er­ates such mar­riage-test­ing stunts such as clean­ing mo­tor­cy­cle parts in the dish­washer, Bryan has re­stored all his bikes him­self, as he ex­plains. “All the work done on the S7, LE and Ariel (ex­clud­ing en­gine ma­chin­ing and chroming) I did my­self (with the bride as­sist­ing with cri­tiquing or sewing pan­nier in­serts). I am say­ing this, not for self­ag­gran­dis­e­ment, rather, too of­ten, restor­ing some­thing be­comes a ques­tion of who’s got the big­gest cheque book, which I re­sent. I would like oth­ers to know, who may just be get­ting in­ter­ested or started in restor­ing things, to be will­ing to give it a go. I have no for­mal train­ing, but I quickly learned, to keep your ears and eyes open to the old timers… and the won­ders of a Hills Hoist clothes line – par ex­cel­lence for hang­ing mo­tor­cy­cle parts, to then, paint them, or an ex­ten­sion lad­der set be­tween two trees. Thank­fully the bride un­der­stood early in the game, the kitchen is a man­u­fac­tur­ing cen­tre…as such...the dish­washer is un­beat­able for fi­nal clean­ing of parts, stove-paint us­ing the oven, etc, and for any­thing too big to wash there’s the bath­tub!” The S8 fea­tured here be­longs to South Aus­tralian John Wat­son. Ray Goul­ter, for­mer sec­re­tary of the Auto Cy­cle Union of NSW, pho­tographed the bike at John’s home. If you’re in the area and fancy see­ing a big bunch of Sun­beams from all eras, not just the S7/8, the an­nual Sun­beams in Oz Rally takes place this year in NSW, based at the pic­turesque town of Glouces­ter near Bar­ring­ton Tops, from Septem­ber 14-15.

An S7 takes pride of place at the Ade­laide Show circa 1949. (Photo: Paul Caine)

FAR LEFT: Brochure of the orig­i­nal 1946 S7 LEFT: Sunbeam ad­ver­tise­ment pre­view­ing the 1948 Earl’s Court Show. ABOVE: Pre-war pre­de­ces­sor of the S7, the short-lived Hi Cam Sunbeam (Il­lus­tra­tion by Alan Puck­ett).

Fac­tory il­lus­tra­tion of the drive shaft with nee­dle roller univer­sal joint at the rear. RIGHT Fac­tory il­lus­tra­tion of the front rub­ber mount­ing. BELOW RIGHT Fac­tory il­lus­tra­tion of the trou­ble­some worm re­duc­tion gear in the rear dif­fer­en­tial.

S8 in gold liv­ery at the 2016 All British Rally. An S7 in the South­ward Mu­seum, New Zealand.

In OBA 59 Jeff Brum­head told of his ex­pe­ri­ences with S7 and S8 Sun­beams. Here is Jeff’s S8, loaded ready for a trip from Vic­to­ria to Queens­land in 1957.

Stream­lined air fil­ter cover. Ig­ni­tion switch and am­me­ter sit in the bat­tery box.

The tired old S7 sit­ting on the shop floor in Kohl’s, New York.

Stan­dard Smiths speedo. Steel fuel lines are a must! Cam­chain ad­juster sits on left side of en­gine. One of the “snub­bers” to coun­ter­act the rock­ing of the en­gine. Large rub­ber mount stead­ies the top of the en­gine. ABOVE Later dip­stick caps were se­cured by a clip. Dis­trib­u­tor sits above the clutch hous­ing. Flex­i­ble joint in ex­haust pipe. FROM FAR LEFT The rear hub and univer­sal joint, hous­ing the of­ten trou­ble­some worm gear; Rear plunger unit bolts have tommy-bar tops to ease rear wheel re­moval; Sin­gle-way damp­ing re­placed the early un-damped front forks; Only the ca­ble ad­juster is ex­ter­nally vis­i­ble on the front brake.

Much slim­mer fork crowns hold the head­light and speedo. ABOVE LEFT 19-inch front wheel with smaller, con­ven­tional brake. ABOVE RIGHT 40-watt Lu­cas dy­namo pokes out the front. BELOW Cast al­loy si­lencer on the S8 re­placed the steel S7 item.

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