Anthony Heal recalls Coatalen’s experiments of 1910-11, which led to the evolution of the successful road-racing Sunbeams of the post-1918 era.
In 1909 Louis Coatalen joined the Sunbeam Moter Co. at Wolverhampton as, chief engineer. He immediately instituted the policy of experiment in design and test in racing that was responsible for building up the reputation of the Sunbeam Company. It was the Coatalen policy that brought the firm to the leading position in the British motor industry that it maintained for so many years, and it was the abandonment of that policy at the time of the economic slump in the early ‘thirties that contributed to, even if it did not wholly account for, the Wolverhampton firm’s downfall.
It may not be generally known that, prior to adopting the L-head side-by-side valve-engine for his 12/16-h.p. 3-litre cars in 1912, Louis Coatalen had designed, built and raced (with varying degrees of success) Sunbeam engines both with vertical and inclined overhead valves, and with push-rod and overhead-camshaft valve operation, as well as motors with the more normal T-head, side-valve arrangement. The epoch-making success of the 1912 3-litre cars that won first, second and third places in the Coupe de l’Auto at Dieppe, and which were third, fourth and fifth in the Grand Prix de l’A.C.F. itself (which was run concurrently) has overshadowed the earlier and, in some ways, more interesting experiments. It is proposed, therefore, to give a short account of three of these early cars in this article.
For many years Sunbeam cars had competed in trials, hill-climbs and races in more or less standard form, so that the appearance of the specially-built, cigar-shaped, single-seater Sunbeam “Nautilus” at Brooklands in March, 1910, caused a good deal of interest and speculation. Coatalen was not only a brilliant engineer and an ardent experimentalist, but he was also a keen publicist, and he quickly realised that to the technical lessons to be gained by racing were to be added appreciable advantages in the way of advertisement. “Nautilus’s” narrow single-seater body was built up of wooden slats mounted on hoops rather in the manner of a barrel, the nose and tail being formed by cones of polished brass. Only the driver’s head protruded through the small cockpit opening. In order to reduce the wind-resistance still further, the front axle carried a streamline fairing and discs covered the wheel spokes. An undershield completely enclosed the underside of the car, and the exhaust pipe was apparently led along inside the car to the opening in the tail cone, instead of protruding from the body.
A small radiator was mounted low down in front of the engine and it was supplemented by another mounted transversely behind the driver’s seat. A small hole (about 4 in. in diameter) in the nose admitted air to the forward radiator, but no provision appears to have been made to provide any air flow to the rear one. The cooling system seems to have been the Achilles’s heel of the car, for the rear half of the body had to be removed when “Nautilus” raced at Brooklands. Even this expedient appears to have been insufficient, as the car boiled badly. In its first race it was baulked by a collision between two other competitors when it had a good chance of success after covering a lap at 77.6 m.p.h. At the 1910 Whitsun meeting at Brooklands, The Autocar reported that “the Sunbeam got away (in the 21-h.p. handicap, 8 1/2 miles) with a fine burst of speed and looked like winning at one period, but all at once it slowed up and was passed by the other three cars owing to lack of water in the radiator causing the engine to overheat.” “Nautilus” was at first run with thermo-syphon cooling, but even the addition of a water pump failed to overcome the overheating trouble.
The engine had four cylinders of 92 by 160 mm. (4,244 c.c.). Sixteen overhead valves were mounted vertically in the cylinder head and were operated, through push-rods and rather lengthy rockers, from two camshafts, one on each side of the crankcase. The weight of the operating gear necessitated the use of very strong valve springs and the rockers caused a good deal of side-thrust on the valve stems. These two factors, according to Coatalen (The Motor, May 19th, 1914) were the cause of the car’s unreliability, but it seems likely that the cooling arrangements must also bear some part or the blame. A forward-facing air scoop on the air intake of the carburetter provided a slight forced-induction effect and this, no doubt, was the cause of statements that had been made that the engine was supercharged. Incidentally, “Nautilus” appears to have been the only chain-driven Sunbeam to have raced at Brooklands.
In 1911, profiting by the lessons learnt with “Nautilus,” Coatalen produced another overhead-valve engine for a very successful racing-car known as “Toodles II.” To overcome the troubles experienced with heavy push-rods and rocker gear, the new engine had a chain-driven overhead camshaft in order to reduce the reciprocating masses to a minimum. The bore of the new engine was reduced to 80 mm., while the stroke remained 160 mm., giving a capacity of 3,215 c.c. The cylinders were cast in pairs and were set 16 mm. desaxé. The cooling of the valve seats and the lightening of the operating gear had evidently been given special study. There were two valves per cylinder inclined at an included angle of 100°. Each valve was mounted in a detachable water-jacketed cage. Each valve cage had its own water off-take branch, and holes in the joint face registered with similar holes in the cylinder water-jacket. The whole of the water flow had therefore to pass through the jackets of the valve cages. 50 mm. diameter tulip valves with hollow stems were used for lightness. To avoid side thrust on the valve stems, the valve springs were enclosed in thimbles which moved in guides, the forked ends of the rockers bearing on the thimbles. A second return spring was used for each rocker.
The camshaft, which was carried in plain bearings, was driven from its front end by a compound roller chain enclosed in an aluminium casing. Trouble was experienced with the chain thrashing and, to mitigate it, a flywheel was fitted to the front end of the camshaft to damp out variations in torque. As was common practice at the time, the inlet valve opened at top dead centre, but the exhaust valve did not close until 12° after t.d.c. The oil pump, water pump and magneto were driven off the crankshaft sprocket on the near side of the engine.
Light steel pistons, turned from solid forgings, had most of their skirts cut away very much like the later Ricardo “slipper” pistons. The piston crown was steeply conical and, with the hemispherical combustion chamber, gave a compression ratio of 5 to 1. With their two compression rings and gudgeon pins complete, these steel pistons only weighed 1 lb. 7 oz. Long, narrow H-section connecting-rods were carefully lightened by a row of 14 holes of graduated size, so that little of the centre web remained. Throughout the whole design great care was obviously taken to reduce the weight of all the reciprocating parts, and one is reminded of Coatalen’s famous saying: “An ounce off the piston is worth a pound off the crankshaft and a hundredweight off the chassis.” At 2,600 r.p.m. the engine gave 63 b.h.p., which was 26 per cent. more than the side-valve racing engines developed from the 80 by 120 mm., 12/16-h.p. model.
Not only was unnecessary reciprocating weight eschewed, but the frontal area of the car as a whole was reduced to a minimum. The narrow, sharply-pointed radiator was built up of oval-section tubes with numerous small conical projections. The air, after passing through the cooling element, was discharged through vents on either side of the bonnet. A bulkhead behind the radiator sealed off the engine compartment. The steering gear was mounted centrally, and a slender single-seater body with a longish, pointed tail was fitted. A smooth undershield ran the whole length of the car.
The chassis was a standard 1910 model with 3/4-elliptic rear springs. Rudge-Whitworth wire wheels were used and Triou hydraulic shock-absorbers damped the axle movement.
During 1911 “Toodles II” won 22 prizes, including a five-mile match race with C. A. Bird’s 60-h.p. Napier at 83 m.p.h., and two short handicap races at the Brooklands Whitsun meeting. Coatalen also broke the 16-h.p. Class Short Record (1/2 mile, flying start) at 86.16 m.p.h. The season’s successes brought the Sunbeam Company and their chief engineer a great deal of very welcome récIame and, in order to follow up the advantage thus gained, another engine was built early in 1912 with a gear-driven overhead camshaft in place of the chain-drive used on “Toodles II.” No record appears to exist of this engine ever having been raced, and this may be due to the fact that the energies of the firm were devoted in 1912 to the preparation of a team of side-valve 12/16-h.p. cars for the Coupe de l’Auto.
As mentioned earlier, this policy paid a handsome dividend when the three basically standard Sunbeams swept the board at Dieppe. Their success was largely due to careful preparation and test at Brooklands, but the experience gained by a lone entry in the 1911 race must also have stood them in good stead. The fact is often overlooked that Sunbeam’s first attempt at international road-racing was the modest entry of a single 12/16-h.p. car in the Coupe de l’Auto in 1911. The car used on this occasion was basically standard. The engine had four cylinders (80 by 149) in a monobloe casting, with T-head. Pressure lubrication was used and the cooling was assisted by a water pump and a fan. A Bosch magneto and a Claudel carburetter were fitted. The cone clutch transmitted the power to a 4-speed gearbox and “live axle.” Third-gear gave direct drive and top was geared up. Rudge-Whitworth detachable wire wheels were fitted and two spares were carried, one on each side of the car. The body work was of roughly streamline form, and the pointed tail bore a striking resemblance to those used on F.I.A.T. racing cars in 1922, and on Bugattis from 1924 onwards. To reduce the time spent at the “ravitaillements,” two filler caps were provided, and a photograph of the car refuelling shows two large “bidons” being emptied simultaneously. The race took place over ten laps of the Boulogne circuit and the total distance was 315 miles. Louis Coatalen shared the driving with T. H. Richards, who had handled the 30-h.p. 6-cylinder Sunbeam during the 12-hour World’s Record at Brooklands. On the first lap the Sunbeam lay 10th, but it climbed to 7th position for the second and third lap. On the fourth round it was passed by Burgess (Calthorpe), but recovered the position by overtaking him on the next lap. The Sunbeam maintained 7th place until it was passed by Porporato’s Gregoire. A skid due to an excess of enthusiasm in an attempt to overtake the French car eliminated the Sunbeam on the eighth lap. Thus ended the Wolverhampton firm’s first entry in an international event. A modest enough beginning to what was to prove to be a long and successful racing career.