The 3-litre twin-ohc Super Sports Sunbeam was among the most interesting of vintage cars, distinguished by its racing-type engine when not many others were so endowed.
News that Louis Coatalen of the Sunbeam Motor Car Company in Wolverhampton had this new car in mind began to circulate early in 1924, but production did not commence until ’25. Its six-cylinder engine had twin overhead camshafts operating two inclined valves per cylinder via sliding fingers for tappet adjustment. Its crankshaft had a vibration damper and ran in seven bearings, as did each gear-driven camshaft. The dimensions of this very advanced engine were 75x110mm (2920cc). Pump lubrication returned the oil to a 4.5-gallon dry-sump tank.
The engine was in unit with a single-plate clutch and gearbox, driving 820×120 tyres, soon changed to 4.25×21. The chassis was virtually that of a 1924 Sunbeam, with cantilever back springs and a somewhat non-sporting wheelbase of 10ft 10.5in, compared to 9ft 9.5in of a Speed Model Bentley. This super sports Sunbeam weighed 27cwt and was geared to give 90mph at 4000rpm. The chassis price was £950 and the four-seater cost £1125. An 80mph Weymann saloon was priced at £1250. With its long bonnet and body and cyde-type front mudguards it was an impressive sight.
Even before news broke of the new Sunbeam a vitriolic correspondence started in The Autocar between WO Bentley and Coatalen, unique as both held such prominent positions in the motoring world. The latter had expressed his belief that building specialised racing cars was essential for the improvement of production cars. This angered WO, who in the 1922 TT had done quite well with near-standard cars, even to relying on rear-wheel brakes only, because his catalogue Bentleys did not feature front-wheel brakes. Coatalen said the Bentleys were based on 1913/14 racing designs, with their single-ohc and four valves per cylinder in pent-roof heads necessitating twin plugs.
The way ahead, said Sunbeam’s engineer, was to use twin valves in hemi heads, with a central plug and six cylinders, as he did with his post-1914 racing cars and his forthcoming sportscar. Coatalen did not know, presumably, that by 1925 WO would reveal the Big Six Bentley. Nor could he, or WO, foresee the meritorious Le Mans and Brooklands performances of these six-cylinder Bentleys in 6.5 and 8-litre form; but maybe Coatalen did not accept them as “special racing cars”. They went to it fiercely with disguised politeness, over some 13 pages of The Autocar.
WO missed a point by not asking Coatalen why, before his new car was ready, he had offered the OV single-ohc, four-valves-per-cylinder engines for existing production Sunbeams. But perhaps WO never knew of these, as I believe that only one OV-powered Sunbeam was submitted for a brief journalistic road test.
Coatalen criticised WO for using open propshafts when torque-tube transmission, which Sunbeams had from 1924, was much superior. When Coatalen said the Sunbeam engines ran at 2700rpm in their celebrated 1912 Coupe de L’Auto 1-2-3 finish, WO responded by saying the car he raced in that year did 3400rpm. But he said he hoped he would never make special racing cars, but that if he did he would get the best man from Fiat or Sunbeam to design them, and set the dog on them if they came near his production cars — subtle irony, because the Sunbeam that had won such great acclaim after winning the 1923 French GP was a Fiat crib!
WO had to apologise to Coatalen for thinking his special racing cars were made in isolated factories and by special designers. (But I thought the racing Sunbeams were constructed in the Experimental shop, which photographs seemed to show was usually full of racing cars.) W said, “The Bentley has never been, and never will be, anything but a touring car.” Coatalen in defending his hemi-head engines quoted the Condor aero-engine with four valves in each such head. It was a great, and very entertaining, verbal contest.
Coatalen entered two Sunbeams for the 1925 Le Mans 24 Hours, in direct competition with the Bentleys. He lined up Jean Chassagne, Segrave, George Duller and Sammy Davis to drive them for him. The Bentleys were in the care of Frank Clement and John Duff, whose Bentley had won the previous year, and Kensington Moir and Dr Benjafield.
This very demanding race opened with a close duel between Segrave and Moir for some 200 miles, until dust from the road jammed the barrel throttles of the Claudel-Hobson carburettors on Segrave’s Sunbeam, and then Moir ran out of fuel five miles before the stipulated replenishment distance. Next, Duff had fuel-feed problems; he ran to the pits for a replacement pump, and Clement took over, but a float chamber broke away and that Bentley was out, too. Coatalen must have relaxed…
But the Sunbeams with their long chassis had their own troubles. Duller pulled out with a useless clutch and Davis/Chassagne had their back axle damaged by being forced down into a gutter — and Davis thrice used the Mulsanne escape road when his throttles jammed. But the engine was fine, holding a continuous 3800rpm, and second place was secured, four laps behind the winning Lorraine of de Courcelles and Rossignol, and one ahead of another Lorraine.
Duller won the Essex MC Six-Hour race at Brooklands in 1927 in a 3-litre Sunbeam with more substantial mudguards, Segrave having run out of fuel. In ’28, six special 3-litres were produced with Noll Cozette superchargers. Sir Malcolm Campbell drove one of these in the ’29 Phoenix Park race, but the clutch disliked 138 bhp. BO Davies ran one in the ’30 race, but retired with supercharger woes, having already lapped Brooklands at over 107mph. GJ Jackson, meanwhile, won at Southport and Blackpool with a non-supercharged car.
The 3-litre Sunbeam was in production up to 1930 and remains one of the finest British vintage sportscars.