Sunbeam S7 De Luxe
The British industry is often accused of a lack of innovation, especially after the SecondWorldWar.But there were exceptions, and some advanced designs.
The history of the British motorcycle industry is littered with innovative and radically exciting designs that promised much but failed to deliver, an example of which is this month's test bike. It's a 500cc twin with the name of Sunbeam on the petrol tank and now owned by West Country enthusiast Steve Morris.
In 1945,with the Second World War coming to its end, there came rumours that BSA were developing a new overhead camshaft inline twin which was set to be a class leader, a model which Small Heath hoped would be snapped up by the bike-starved population. Sadly this was not the case and subsequent sales were disappointing.
During the war, it was standard practice for captured enemy vehicles to be evaluated by makers of similar bikes and in England, BSA had been given a stream of BMW, Zundapp, NSU and DKWs to examine very carefully for their range of postwar machines. The R75 Army issue scored highly for both its comfort and handling, but BSA felt that an OHV flat twin would shout 'copy' from the rooftops from prospective customers, who would not be very pro-German so soon after the war. During 1946, a search was made for a suitable engine and for this Small Heath secured the services of Erling Poppe, an engineer and designer whose family firm of White and Poppe had been responsible for making the engines for the original Bullnose Morris motorcar in the 1920s.
The first Sunbeam motorcycle, powered by a 350cc side-valve engine, had been manufactured in 1912and quickly earned the name of 'The Gentleman's Machine; a quality bike with real gold leaf used for the lining on the petrol tank. Despite the death of the company's founder John Marston (aged 82) in 1918,the Wolverhampton factory continued to make beautifully constructed - and often very fast - machines, winning the Senior TT in 1920 and 1922.
There were two more TT wins in both 1928and 1929 with Charlie Dodson in the saddle, but by this time, the depression began to tighten its grip and in 1928the company was taken over by ICI. Under the umbrella ofICI, there was little change to the range of mostly overhead and side-valve single cylinder models, but then, in September 1937,the motorcycle production and trademark were sold to the giant AMC empire.
AMC was very much aware of Sunbeam's previous racing successes and went about designing a new line-up of sporting singles for the 1939season. Still in the traditional black and gold livery, they proved to be both well made and reliable but were only in production for one year before the Second World War brought production of civilian machines to a halt.
In addition to the motorcycles, the Sunbeam Wolverhampton factory also manufactured a range of top quality pedal cycles and in 1943,with an eye to the end of the war, BSAwere keen to match the cycle output of rival Raleigh and on November 25, a deal was struck with AMC whereby the cycle and motorcycle manufacturing rights went to Small Heath. It signalled the end of the road for the superbly engineered Sunbeam singles but BSAwas very much aware of the kudos the name carried and it was decided to use it on the new inline twin, a model which the Small Heath management considered would carry on the traditions of the late John Marston and become the postwar reincarnation of 'The Gentleman's Machine'.
Their new recruit Erling Poppe had looked hard at the BMW layout but had decided to use a concept which had been lying about in the experimental shop since 1932, an inline twin known to all who worked on it at BSA's factory at Redditch as the 'LAT;Prototypes of the new single overhead camshaft S7 - the designation of which is now unknown - were tested during 1946,but initially the high revving engine proved to suffer incredible vibration problems, which, period reports are to be believed, saw one early test model returning to base with the engine hanging from the frame.
Hazardous affair
The high-revving, short stroke engine produced plenty of power with a top speed of around 90mph but, as was quickly discovered, the vibration caused serious wear in the worm drive and on the road the 'peaky' power delivery of the prototype twin saw it twitching to the right, making going up through the four-speed gearbox a slightly hazardous affair. With its block-tread 4.75 x 16in tyres, the handling of the S7 was certainly 'suspect' too and it soon became apparent that the poorly designed cylinder head allowed large quantities of oil to collect around the rockers, which starved the bearings, resulting in spectacular failure.
It was thought that the major problems would disappear if there was less power from the 500cc twin and the famous George Dance - a genius of the competition department at the old Sunbeam Wolverhampton factory - was invited to test ride a number of prototypes.
He was not overly complimentary of the rather portly inline 4oolb twin, which now featured flat combustion chambers and inline valves in the engine unit, which was now tilted forward by three degrees. This had cut the output to a rather meagre 23.6bhp, which helped the handling and reduced the rear drive wear, but emasculated the performance, leaving the S7 on the
verge of being underpowered for a 500cc machine.
Road testers reported that the prototypes still suffered the old vibration issues, but their concerns and criticisms weren't what the BSAmanagement wanted to hear, so they were ignored, and a limited batch were put into production and sent to South Africa for police use during a royal visit. It was only when they were returned as 'being unrideable' that BSA'smanagement conceded that the excessive 'vibes' might be a deterrent to sales and something needed to be done. Their answer was to rubber mount the engine.
Adopting this important modification took time to implement and it wasn't until October 1947that a proper road test of the rubber-mounted Sunbeam appeared in TheMotor Cycle magazine. Two-and-a-half years had passed since the first hints of the new model had been put out by BSA'spublicity machine and any customer interest fired up by articles in the Press had largely been lost and, apparently, designer Erling Poppe was given 15 minutes to clear out his desk and leave the works.
But BSAwere not giving up on the idea of a
'gentleman's tourer' and in 1949two new models burst upon an indifferent world, in the form of the S7 De Luxe and the more sporty SB.This month's test bike, finished like all S7 De Luxes in Sunbeam's mist green and carrying the number of 315GRP,was supplied by Aldershot, Hampshire, BSAagents Phillips Brothers and first registered on January 5, 1952,at the on the road price of £190. Little or nothing of the Beam's subsequent history is known about but five decades on it was restored by David
Gardner and later sold to Midlands-based enthusiast Bernard Lance bury who, in 2015,moved it on to its present keeper Steve Morris.
Steve started his motorcycling life in the 1970swith a 50cc Garelli Tiger Cross, a bike plus helmet he bought for £12,which kick-started his two wheeled career. Fast forward to 2020 and he now has an eclectic collection of bikes, the S7 De Luxe sharing space in his well-equipped workshop with many others including a beautifully, recently restored Tiger Cross, an original, low mileage Sunbeam SBand a previously-featured in these pages Vincent Comet. There's no doubt that the softly tuned
- and rather portly - S7 Sunbeam is a very different machine to the Stevenage single, but as I would later discover it's an ideal one for negotiating the superb back roads in its new home in West Wiltshire.
From its release in 1949until its demise in 1956there was little in the way of substantial alterations to the overall layout and design of the Sunbeam and with no serious attempt from BSAto market them, only 5554 examples of the shaft driven 500cc inline twin would ever roll off the Redditch production lines.
In many ways the Sunbeam could have made for an ideal sidecar machine, but in reality it was rather asthmatic and, as was soon discovered, was not the best for dragging double adults up steep hills. The factory's experimental department was aware of this and went about manufacturing a 600cc prototype, but due to the fat loss the parent company were making, none ever reached the production stage.