Sunbeams Between the Wars

by John R. Coombes and John Wyer 

The heading above refers, not as might be thought to the happy times we enjoyed between World War 1 and World War II, but to the cars manufactured during that period by the Sunbeam Motor Car Company Ltd., of Wolverhampton. It is particularly opportune that we are able to publish this article in this issue, because this is the Jubilee year of Sunbeam, whose first car was made in 1899. The matter which follows is the work of John R. Coombes, whose father was advertising manager to the Sunbeam Company from 1919 to 1923 and who himself was, until recently, with the Sunbeam Trolley-bus concern in the old factory, and John Wyer, who served his apprenticeship with Sunbeam while they were still making private cars. Anthony Heal, whose interest in, and collection of, historic Sunbeam cars is well known, contributes a foreword, and Motor Sport is indebted to these three gentlemen for the great pains they have taken over the accuracy and continuity of this exclusive contribution. For many years Sunbeam built cars that were esteemed all over the world on account of their typically British quality and performance and notable refinement of running and control, and their racing department gained for this country the honour of winning the 1923 French Grand Prix and of building the first car to exceed 200 m.p.h. Something of the esteem in which Sunbeam is still held in Wolverhampton, its birthplace, is seen in the three-quarter-length portrait of Segrave which hangs in the entrance hall of the Bantock House Museum in that town. At the present time, in comparison with some vintage cars the Sunbeam can be described as "popular," for a surprising number of the o.h.v. "14/40s" are still on the road, the number of later six-cylinder models in service is legion, while as recently as last July the twin-overhead-camshaft 3-litre proved its prowess at Silverstone. Consequently, we present this article confident that not only will enthusiasts in general find it of great interest, but that it will be of considerable value to owners and prospective purchasers of Sunbeam cars, in the Jubilee year of this famous and respected British make. — Ed.​

Not in vain the distant beacons, forward, forward, let as range,
Let the great world spin for ever down the ringing groove of change;
Thro' the shadow of the globe we sweep into the younger day,
Better fifty years of Europe than a cycle of Cathay.

(Tennyson)

It is half a century since the first Sunbeam car was built in a disused coach house in Wolverhampton. John Marston had already made a handsome fortune in 1899 and his Sunbeam bicycles had achieved for themselves a reputation for quality and finish. Many thought him foolish to risk the hard-won fruits of many years pioneer work in the cycle trade on such a hazardous venture as the new-fangled "horseless carriage." He was persuaded into it by Thomas Cureton who had joined Marston's cycle works as an apprentice and had since risen to become his trusted lieutenant. Cureton made the first experimental Sunbeam car, in its entirety, with the help of one man and a boy. After trials on Sunday mornings in the privacy of his garden, John Marston decided to back Cureton's brain-child, and in 1900 a second car was produced. The first Sunbeam car catalogue, entitled All about a Motor Car, was published in the same year and the verse from Tennyson's Locksley Hall, printed at the head of this Foreword, was quoted in it. It seemed opportune, therefore, to recall it on this occasion of the Sunbeam Jubilee.

Foreword

The informative article by John Coombes and John Wyer which follows, deals with the Sunbeam cars that were built between 1919 and 1985. This brief foreword can serve only to sketch broadly the developments that took place during the first two decades of the firm's history. Space does not permit a detailed account of the machines produced from 1899 to 1919, nor is it possible to make more than a passing reference to the racing and competition successes that they achieved. The latter subject really deserves a special article of its own. The development and achievements of Sunbeam aero-engines, in war and in peace, is another side of the firm's activities that merits more detailed attention than we can give it on this occasion.

Cureton's first experimental car appears to have been fitted with a single-cylinder engine mounted vertically at the front. Transmission was by belt and the high wooden road wheels were shod with solid rubber tyres. The second car, produced and catalogued in 1900, had the engine in the then more fashionable horizontal position. It was equipped with the up-to-date "electric ignition" and is said to have developed 6 b.h.p. at 700 r.p.m. Belt transmission was retained and a two-speed gear added. In 1901 the firm entered into an arrangement with a Mr. Mabley-Smith to produce a very peculiar four-wheeled vehicle, which is probably already known to readers of Motor Sport — the Sunbeam-Mabley. Despite the unusual design (rather like an S-shaped Victorian sofa) these machines were made in some quantities and were sold at the modest price of £130. Mr. Mabley-Smith drew a royalty on each one and, it is said, he made more out of each Sunbeam-Mabley sold than did John Marston. At the 1901 Crystal Palace Motor Show the Mabley was shown alongside a new twin-cylinder Sunbeam which embodied a number of up-to-date improvements including wheel steering, raked steering column and band brakes working on drums (in place of shoe brakes operating on solid rubber tyres as on earlier models).

A four-cylinder 12-h.p. car was introduced in 1902 when Thomas C. Pullinger joined the firm as Works Manager. He persuaded Marston and Cureton to swallow their pride and import some French-built cars in order to learn from the more advanced industry of France how motor cars were really made. For some time afterwards engines and gearboxes were imported from Lyon to be mounted in chassis made in Wolverhampton. Thus began a connection with France that continued until the eventual demise of the Sunbeam Motor Car Company, Ltd., in 1985. As on subsequent occasions in the history of the firm this injection of French ideas resulted in the production of a successful car. The 10/12-h.p. (4-cylinder 80 by 120 mm.) not only proved to be the mainstay of the business, but served to enhance Sunbeam's reputation in competitive events. Two cars of this type made non-stop runs, without losing a single mark, in the Glasgow-London Non-Stop Trial organised by the A.C.G.B.I. (latterly known as the R.A.C.).

Behind the scenes work was quietly going on during the summer of 1908 with the testing of a new six-cylinder engine which was added to the range of Sunbeam cars offered to the public in February, 1904, barely four months after S. F. Edge had announced his intention of producing a six-cylinder Napier. Possibly as the result of Edge's propaganda (he was an accomplished publicist) Napier's claim to have built the first "six" is regarded by some as proven, but others (notably Sunbeam, Brooke and Maudslay) might well contest the claim.

John Marston's motor-car business waxed slowly but surely as the qualities of the cars he built came to be recognised. In 1905 a £40,000 company was floated with Marston and Cureton as two of the directors. W. M. Iliff's name appeared on the prospectus as Secretary. A new and more powerful model, designed by Angus Shaw, chief of the newly-established drawing office, was produced. Known as the 60/20-h.p., it had a four-cylinder engine (95 by 120 mm.), magneto ignition and honeycomb radiator (earlier cars had all used gilled tubes), four speeds and, of course, chain drive in "little oil bath" chain cases. To demonstrate his faith in the new car, Shaw set off with Frederick Eastmead in June, 1906, to drive an open four-seater from John o'Groats to Land's End and back again to John o'Groats (1,757 miles) without stopping the engine. This performance was officially observed by the Scottish Automobile Club who provided relays of hardy observers to ride in the back seat. The engine ran non-stop for 95 hours 56 minutes and "no repair or adjustment of any kind took place during the whole period." The Sunbeam Motor Car Company was now, quite definitely, "on the map" and was steadily producing cars at the rate of ten per week. The successful 16/20-h.p. was continued in 1907 and a six-cylinder 25/30-h.p. model with the same bore and stroke (95 by 120 min.) was added.

The first ten years had been a period of struggle, experiment and test. The decade that followed was to witness achievement and success, due largely to the genius of one man. In February, 1909, Thomas Cureton engaged a young Frenchman, Louis Coatalen, as chief engineer and once again the injection of French ideas revitalised the whole concern. Coatalen's influence spread throughout the works; he inspired the design, supervised the manufacture and himself tested the completed cars. He re-designed the 16/20-h.p. car, enlarging the dimensions to 95 by 135 mm. and he produced a new smaller model known as the 12/16-h.p. (four-cylinder 80 by 120 mm., T-head). The latter was an immediate success; 350 were made in 1910 and 650 in 1911. As a result the works had to be enlarged to deal with the volume of orders. In 1911 a worm-driven rear axle replaced the chain drive and two new six-cylinder models were introduced; 25/30-h.p. (105 by 135 mm.) and 18/22-h.p. (80 by 120 mm.). The 16/20 four-cylinder car was continued.

An ardent experimentalist, Coatalen soon took advantage of the facilities offered by Brooklands for testing cars and standard Sunbeam chassis gained many successes there. But not for long was he content to race only production models and in 1910 a special overhead-valve four-cylinder (92 by 160 mm.) engine was built and fitted in a chain-driven chassis. The radiator was mounted behind the driver and the narrow single-seater cigar-shaped body enclosed everything but the driver's head. Although quite fast the car (known as Nautilus) was prone to overheating. Another special racing car (Toodles II) was built in 1911. It was fitted with a four-cylinder (80 by 160 mm.) overhead camshaft engine and was much more successful than its predecessor. In the same year Coatalen completely redesigned the 12/16-h.p. model, using a new monobloc (80 by 150 mm.) L-head engine and a bevel-driven rear axle. One of these cars was driven in the 1911 Coupe de l'Auto race for 3-litre voiturettes by T. H. Richards. This was the first appearance of the marque in an international event on the continent. When lying seventh, Richards had to retire with a broken steering connection.

For the 1912 race at Dieppe a team of three 12/16-h.p. cars was prepared and they swept the board, finishing first, second and third in the Coupe de l'Auto and third, fourth and fifth in the Grand Prix itself, which was run concurrently. These basically-standard side-valve 8-litre machines beat all-corners save a couple of specially-built Grand Prix racing cars of twice and three times the Sunbeam's capacity. This great success (the first British victory since Edge's Gordon Bennett win in 1902) firmly set the Sunbeam company in the van of British constructors, which position it was to retain for fifteen years. Coatalen's part in the achievement was recognised and he was elected a director of the company. He redesigned the 16/20-h.p. and the six-cylinder 25/30-h.p. models on lines similar to the 12/16-h.p. car and this three-model range was continued until the outbreak of war in 1914. During the hostilities the two smaller models were supplied to the War Office for use as staff-cars in France and to increase the supply some were built, under licence, by the Rover Company. Since 1913 Coatalen had been developing Sunbeam aircraft engines and to meet the needs of war their production was greatly increased. The firm's experience of high efficiency engines for racing cars stood them in good stead, and their 1914-1918 aero-engines show many signs of a close family relationship with the power-unit of the 1914 Grand Prix Sunbeam.

Louis Coatalen and W. M. Iliff were appointed joint managing directors in the year 1914, and four years later John Marston, the chairman of the company and founder of the firm, died at the age of 82. Thomas Cureton, who since his apprenticeship, had worked with Marston and had been instrumental in persuading him to branch out into the manufacture of motor cars, fittingly succeeded his chief as chairman. He occupied the post for little more than two years and died in 1921, shortly after his retirement. In August, 1920, the Sunbeam Motor Car Co. amalgamated with A. Darracq & Co. (1905), Ltd. The latter concern had, in the previous year, already absorbed the Clement Talbot Motor Co. as well as the well-known firm of spring-makers, Jonas Woodhead & Co., the engineering firm of Heenan and Froude, whose dynamometers are well known and H. du Cros, the coachbuilders. Three Sunbeam directors joined the board of the new combine which marked the amalgamation by changing its name to S.T.D. Motors, Ltd. Mr. James Todd, chairman of S.T.D., became chairman of the Sunbeam company. Thus three famous firms, each of whom had accomplished great things in racing and record-breaking on road and track, joined forces and the motoring public awaited the outcome with great expectations.

It is sometimes said that the products of firms who engage in Grand Prix racing derive the least benefit from it. A superficial look at some of the cars such firms have built might tend to support this view. But racing has more than just technical value and to the Sunbeam company it was the mainspring of their endeavour. To Louis Coatalen it acted as a spur and the hundreds of men he employed felt an intense pride in the success of the Sunbeam racing cars. So long as Sunbeams "wore the green" in international Grands Prix every man was "on his toes " and the firm maintained its technical leadership. Coatalen was the creative genius who inspired and led the team, but he was ably supported by three stalwart lieutenants: J. S. Irving, the experimental and development engineer, who put his chief's ideas into tangible form; Clement Kaye, the works manager, who organised production, and Leo Cozens, the sales manager, who kept the Sunbeam company's products and their achievements constantly in the public eye.

In 1926 the racing activities of the S.T.D. group, of which the Wolverhampton firm was the senior member, were transferred to the Talbot-Darracq works at Suresnes, near Paris, and Coatalen's attention was largely devoted to the French unit of the combine. With his influence now removed from Wolverhampton and in the absence of the racing cars the momentum of the firm began to be lost. Their technical leadership was no longer maintained and the company, unable to withstand the stress of the economic depression of the early nineteen-thirties, got into financial difficulties from which it never recovered. In 1935 Sunbeam cars ceased to be manufactured at the Moorfield Works, Wolverhampton. As the pessimists had forecast, John Marston's Sunbeam bicycles had survived his horseless-carriage venture. Such then was the backcloth against which the Sunbeam cars described by John Coombes and John Wyer "had their exits and their entrances."
Anthony S. Heal.

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The range of production models marketed by the Sunbeam Motor Car Company between the end of the bow-and-arrow war and the cessation of production in 1935 is so extraordinarily complex and varied that it is extremely difficult to trace any sort of consecutive theme, to see any logical progress between one model or series of models and those which followed. Closer examination, aided by a fairly intimate knowledge of the more detailed design changes begins to reveal a broad pattern, and the period under review sub-divides itself into reasonably well defined phases. While there are inevitably some borderline cases, it will generally be found possible to fit each model into its respective phase or group, and we might start by listing these phases, with the principal design features by which they may be identified.

Phase I. 1919-1921. 80 by 150 sidevalve, 16-h.p. four-cylinder and 24-h.p. six-cylinder cars, directly descended from the 1914 models, from which they differed in only very minor details. Cone clutches, separate gearboxes, open propeller shafts and ½-elliptic rear springs are outstanding features.

Phase II. 1922-1924. The first overhead valve engines. Based upon the Phase I side-valve cars, with the same range of models, but now known as "16/40" and "24/60" (later "24/70 "), the only changes were in the cylinder blocks and heads, the latter now being detachable. Chassis design was unchanged but four-wheel brakes were introduced during Phase II. 

Phase III. 1922-1932. An entirely new overhead-valve engine and an entirely new chassis. The first Sunbeam design to have the inlet and exhaust ports emerging on the same side of the head. Chassis changes include unit gearbox, torque-tube and cantilever rear springs. Models comprised the "12/30," "14/40," "16/50" and "20/60," the straight-eights, and the 25-h.p. which was listed until 1932. This phase continued the earlier tradition of aluminium crankcases and separate cast-iron blocks, although the short-lived "12/80" and "16/50" were exceptions. (This is the sort of thing which makes life difficult for the historian with the pigeon-hole type of mind.)

Phase IV. 1927-1935. This period saw the stabilisation of design rather than any striking changes. The single iron casting for crankcase and block was finally adopted, and units became generally tidier and more compact (and cheaper to produce). Chassis design also followed earlier practice, but ½-elliptic rear springs came back into fashion in 1930, and the open propeller-shaft on some models in 1935. It is, however, probably true to say that from 1927 onwards Sunbeam ceased to lead the industry in any important particular, and it was this more than any other factor which led to their final downfall.

This attempted summary is admittedly an over-simplification, and the difficulty of making any cast iron divisions is very apparent. Also it will at once be noted that the actual date of manufacture bears little relation to identifiable features of design, and there is considerable overlapping between the phases. The present writers hope to show, however, that design did, in fact, follow these general lines and that some steady, if unspectacular, progress was made. Let us now look at things in more detail.

Phase I
The 80 by 150 Four and Six-Cylinder Cars

These were the first post-war models introduced by the Sunbeam Company, and were, like so many latter-day "postwar" cars, slightly improved versions of the pre-war types. They were known as the 16-h.p. and 24-h.p. models, respectively, and were developed from the very successful Coatalen-designed "12/16"and "25/30" cars which had been in production since 1910. The major changes were: —

(a) Semi-elliptic instead of ¾-elliptic rear springs.
(b) A lighter, neater (and apparently weaker!) rear axle design.
(c) Cam-operated rear wheel brakes instead of toggle-operation; and
(d) A taller, narrower radiator. (This was introduced during the war, when the "12/16" was being built in quantities by the Rover Company.)

The general design of both models was similar, many components being interchangeable. Bore and stroke were 80 by 150, giving capacities and ratings of 3,016 c.c. and 15.9 h.p. for the "four," and 4,524 c.c. and 23.8 h.p. for the "six." The "four" was a monobloc iron casting, while the "six" was cast in two blocks of three. The cylinders were set approximately 20 mm. désaxé, and the L-heads were non-detachable.

The aluminium crankcase was extended well below the crankshaft, which was carried in split, white-metalled bronze bearings. The four-cylinder engine had five bearings and the six-cylinder had seven. The connecting rods were H-section steel stampings with white metalled big-ends. Cast-iron pistons carried three compression rings with a scraper in the skirt, and the hollow, floating gudgeonpins were retained by a wide ring round the waist of the piston. A silent chain-driven camshaft operated the valves, which were set slightly inclined in the near side of the block, through the medium of roller tappets. The single valve springs were retained by cotter pins through the valve stems.

On the 16-h.p., a cross-shaft, driven by skew gears from the front of the crankshaft, drove a magneto on the off side and a water impellor on the near side. On the 24-h.p., the off-side-mounted magneto was driven by a silent (inverted-tooth) chain, and the water pump, also chain-driven, on the near side, had its spindle extended to drive the dynamo via a long, fabric-jointed shaft.

On the off side, a vertical carburetter, originally S.U., and afterwards Claudel-Hobson, fed into a water-heated manifold, the inlet ports being cored right through the block. The sparking plugs were screwed into the inlet valve caps. The exhaust manifold, heavily finned, was on the near side of the block.

Lubrication was by a gear-type pump driven by skew gears from the camshaft. Cooling was by a honeycomb radiator, assisted by a large cast aluminium fan driven by a leather-link belt from the camshaft on the "four," and from the magneto drive on the "six."

The flywheel incorporated a leather-faced cone clutch, from which the drive went via a short, jointed shaft to a three-point mounted, four-speed gearbox with right-hand gate control. Ratios for both models were: 3.59, 5.3, 7.82 and 11.92-to1; whilst, strangely, the 24-h.p. long wheelbase limousine had a 3.4-to-1 axle and larger (880 by 120) tyres.

A foot-operated transmission brake was fitted behind the gearbox, the hand-lever operating cast iron-faced shoes on the rear wheels. All gearbox shafts ran in ball bearings, and this layshaft was alongside the mainshaft. The selector gear was mounted at the side of the box, which seems to be becoming advanced modern practice! The solid open propeller-shaft had an enclosed joint at the front, and a pot-type joint at the rear. The 1919 rear axle had a curious offset differential, the near-side shaft being about two inches shorter than the off-side. Spiral bevel gearing was used, and the differential was a two-star bevel type. The hubs were originally fully floating, but a ¾-floating axle was introduced later. Ball bearings were used throughout.

For 1920 and 1921 a much heavier axle casing was re-introduced, which carried a straddle-mounted bevel pinion, a spur gear differential and an even larger number of ball bearings!

The front axle was of normal reversed Elliot type, and wheels were wire or artillery to choice, both types having Rudge-Whitworth hubs.

The frame was of pressed steel channel throughout, and was kicked up over the rear axle. In plan view it was notable for the sharp insweep at the scuttle, and could hardly be accused of undue rigidity in any plane. The 24-h.p. had a king-post bracing under the sidemembers. The wheelbase was 10 ft. 4 in. for the 16-h.p. and 11 ft. 4½ in. for the 24-h.p., the long wheelbase 24-h.p. being 12 ft. 0 in. Track (all models) was 4 ft. 6 in. Tyre size was 820 by 120.

Phase II
O.H.V. Engines Introduced

The side-valve cars were in production until the 1921 Motor Show, when they were superseded by the "Phase II" models, which consisted of new push-rod o.h.v. engines in the existing chassis. The new engines were still of 80 by 150 mm., and, indeed, the bottom half was identical with the side-valve units. It is believed several s.v. cars were converted to the new specification. Both four and six-cylinder blocks were monobloc iron castings, with detachable heads.

The valves (two per cylinder) were in line, and the valve-gear was enclosed in a neat cast aluminium cover. The manifolds were still on opposite sides of the unit, and aluminium pistons were used. The two models were now known as the "16/40" and the "24/60," the implied brake horse powers probably being slightly optimistic. The only major chassis change was the use of a 4-to-1 rear axle, although the "24/60" Sports retained the 3.59-to-1 ratio. The track of the larger car was increased to 4 ft. 9 in., and the tyre size on the long wheelbase "24/60" was increased to 895 by 135, with the 4-to-1 axle.

During 1922 and 1923 the extremely attractive Sports Tourers were available (at extra cost) with the very interesting "O.V." engines. These were also of 80 by 150 mm. cylinder size, but were of entirely new design, having inclined overhead valves, which were operated by rockers from a single overhead camshaft. The camshaft was driven by bevels from the front of the crankshaft, via a vertical shaft which incorporated a tongue and slot to accommodate thermal expansion of the block. Double valve springs were used, retained by split collets, and tappet adjustment was by setscrews in the rockers.

The detachable cylinder head carried four valves per cylinder, and ignition was by two coils and distributors feeding two plugs per cylinder.

The crankcase was an aluminium casting, split on the crankshaft centreline, the block being an iron casting. The engine was originally laid out in 1919 as a 75 by 150-mm. unit with the block east integral with the crankcase top half. These "O.V." engines were not désaxé, and with their detachable heads and single o.h.c., must have been a more practical proposition for the owner-driver (and the factory) than the later and more famous 3-litre twin o.h.c. six.

The "O.V." engines, together with the later 3-litre, are of particular interest in that they are the only attempts by Sunbeam to make a direct application of their successful racing designs to production models. The "O.V." is obviously an adaptation of the 1914 racing design, and shows Henri influence. The much better known 3-litre, on the other hand, was developed from the winning 1923 Grand Prix design, and descends from the Bertarione, or Italian, school.

The six-cylinder push-rod engined car was continued for 1924, and was known as the "24/70," though whether the power output had increased is open to doubt. The only notable design change was that four-wheel brakes (with gearbox-driven servo) became standard instead of £125 extra as in the previous year.

The "16/40" was superseded in 1924 by the entirely new six-cylinder "16/50."

Phase III
The First Truly Post-War Design

The first entirely new Sunbeam car appeared towards the end of 1921, and was known as the 14-h.p. model. The chassis layout of this car was to form the basis for Sunbeam touring car design for the next ten years or so, and is therefore worth examining in detail. The engine was a four-cylinder of 72 by 120 mm. (1,954 c.c. and 12.8 h.p.), and had push-rod o.h.v. It differed considerably from the larger "16/40," how ever, having a monobloc aluminium casting for the cylinder block and crankcase top half. Shrunk-in steel liners were used, with aluminium pistons. Floating gudgeon-pins were retained by circlips. This engine was the first built by the company with the manifolds hot-spotted together on the off side of the cast iron head.

Two tulip-headed valves per cylinder were employed, closed by double springs, and operated through mushroom tappets. A single vertical Claudel-Hobson carburetter was fitted, and ignition was by coil and distributor, with automatic advance.

The crankshaft ran in three bearings, and drove the camshaft by silent chain. Cooling was by pump and fan, and the dynamo was driven by Whittle belt from the crankshaft.

A single dry-plate clutch and three-speed gearbox were mounted in unit with this engine, and ratios were 4.5, 7.92 and 13.19-to-1, reverse being 13.19 also. The propeller-shaft was enclosed in a torque-tube, with a spherical joint behind the gearbox. The semi-floating rear axle had spiral bevel drive, a two-star bevel differential, and the casing was fabricated from two steel pressings welded together.

Rear suspension was by cantilever springs, the front springs being asymmetrical semi-elliptics as on the larger models. Brakes were fitted on the rear wheels only, separate sets of fabric-faced shoes being employed for each system. Brake drums were of aluminium with shrunk-in steel liners.

Bolt-on steel artillery wheels were shod with 815 by 105 tyres. Steering was by worm and sector, and the right-hand gear change had no visible gate. Wheelbase was 9 ft. 10½ in. and track was 4 ft. 3in.

The 14 h.p. was continued in 1923 with considerable engine modifications. The block now became a separate iron casting, magneto ignition with manual advance was adopted, the dynamo being incorporated in the magneto drive on the near side of the engine. A fan was optional, and the valve cover was deeper and more square-cornered. The track was increased by 3 in., the brake drums were steel pressings, and the foot brake shoes were faced with cast iron.

1924

The year 1924 saw the introduction of a wide range of models, comprising new "12/30," "16/50" and "20/60" cars, whilst the 14-h.p. was considerably modified and became known as the "14/40," and hence either set or followed the prevailing fashion in nomenclature.

Of the "12/30" little need be said. The catalogue stated that it was introduced in response to the demand for a smaller version of the 14-h.p., but this demand must have been more vocal than actual, as very few of this model were built. Bore and stroke were 68 by 110 mm. (1,598 c.c. and 11.4 h.p.), the block and crankcase was a monobloc iron casting, but the layout was otherwise identical with the 14-h.p. The clutch, gearbox and rear axle were standard 14-h.p. parts, but the final drive ratio was 4.9-to-1. Tyres were 765 by 105, the wheelbase 9 ft. 7 in., and the track 4 ft. 6 in.

The general design of the "14/40" remained similar to the 14-h.p. car, but the bore was increased to 75 mm., raising the capacity to 2,120 c.c. and the R.A.C. rating to 18.9 h.p. A new inlet manifold did considerably less violence to the mixture flow than hitherto.

The gear-change now had a visible gate and a reverse catch. Rod-operated four-wheel brakes, without servo assistance, were available at £35 extra.

An attractive sports four-seater was marketed, for which 50 b.h.p. at 3,000 r.p.m. was claimed. Power claims up to about this time should be regarded with slightly raised eyebrows, as the dynamometer equipment available was probably somewhat bucolic!

The chassis layout of both the "10/50" and "20/60" models was scaled up from the "14/40," wheelbases being 10 ft. 9 3/8 in. and 10 ft. 11 3/8 in., and tracks 4 ft. 7 in. and 4 ft. 9 in., respectively. The LWB "20/60" had a wheelbase of 11 ft. 5 3/8 in.

The "16/50" was a six-cylinder of 70 by 110 mm. (2,540 c.c. and 18.2 h.p.), and the block and crankcase were cast in one. Push-rod operated o.h.v. were used, with double springs. The crankshaft ran in seven bearings.

The "14/40" clutch, gearbox and back axle were used, but Rudge-Whitworth wire wheels shod with 820 by 120 tyres were fitted.

The new six-cylinder "20/60" had the same bore and stroke as the "14/40," giving 8,181 c.c. and 20.9 h.p., and had an aluminium crankcase with a separate iron block. Push-rod o.h.v. were used, as on all Sunbeams henceforth, with the notable exception of the 3-litre. The layout of auxiliaries on all these push-rod engines was similar, comprising a silent chain drive inside the timing-case, extended to the near side of the engine. The water pump was mounted either in front of, or behind, the timing-case, and a rearward shaft extension drove the dynamo through a vernier coupling, a similar coupling behind the dynamo driving the magneto.

On the "20/60" the transmission consisted of a single dry-plate clutch conveying the drive to a unit-mounted four-speed gearbox. Gear ratios were: Normal: 4.5, 6.5, 9.9 and 18.1-to-1; reverse 16.7-to-1; and L.W .B.: 4.77, 6.9, 10.5 and 19.1-to-1; reverse 17.7-to-1.

The 1924 range was completed by the "24/70," which was described with the earlier. 80 by 150-mm. cars.

1925

A simplified range of three models was offered in 1925, comprising the "12/30," the "14/40" and the "20/60." The only major chassis changes were the adoption of worm and nut steering and four-wheel brakes as standard on the "14/40." The few "12/30s" that were built continued to rely on the more gentle retardation provided by rear wheel brakes.

The power output claimed for the "14/40" was 41 b.h.p. at 2,800 r.p.m., on a c.r. of 4.6-to-1. The wheelbase was increased by 1 in., and a much more comprehensive range of bodywork was marketed on both the "14/40" and the "20/60" chassis.

The famous 3-litre was announced as a sports racing car in the spring of 1925, and by finishing second in that year's Le Mans race, ahead of the Bentleys, may be said to have justified its design. In view of the results of the Bentley-Sunbeam match race at this year's B.D.C. Silverstone meeting, it seems that this model can still hold its own against the 3-litre Bentley. (Any comments from Bentley owners?) As the 3-litre was not offered for sale until the 1925 Motor Show it will be described amongst the 1926 models.

1926

The "12/80" had by now died a natural death, and the 1926 range comprised the well-tried "14/40" and "20/60" models, supplemented by a new straight-eight called the "30/90," and the 3-litre.

Few changes were made to the "14/40," but body weights having risen, as body weights have a habit of doing, a 4.72-to-1 axle ratio was used for open cars, and a 5-to-1 axle for the saloon. The "20/60" was virtually unaltered.

The layout of the new straight-eight followed the usual recipe, although an embryonic form of cruciform frame bracing was employed behind the gearbox, consisting of two channel pressings mounted back to back, with their legs spanning about one foot of side-member length. The cantilever rear springs were very massive, and double Hartfords were fitted all round. The chassis was made in two lengths: 11 ft. 5 3/8 in. for open cars, and 12 ft. 8 in. for closed models, the tracks being 4 ft. 9 in. and 4 ft. 11 in., respectively.

The engine in each case was a straight-eight with push-rod o h.v., and of normal Sunbeam design. The very robust crankshaft ran in nine bearings, and carried a large vibration damper at the front end. The camshaft was driven by gears from the front of the crankshaft. The crankcase was of aluminium, and the block was a separate iron casting. The cylinder head was in two portions, each covering four bores, and carried two tulip valves per cylinder. Double valve springs were used, and the auxiliary layout followed normal Sunbeam practice.

The stroke was 120 mm., and the bore for both lengths of wheelbase was originally 80 mm., giving a rating of 31.7 h.p. and a swept volume of 4,826 c.c. The bore for closed models was soon increased by 5 mm., giving 35.9 h.p. and 5,447 c.c.

A double plate clutch conveyed the power to a four-speed gearbox with r.h. control, but the gear-change on the "eights" lacked the delightful ease of almost all other Sunbeams, owing to the rotational inertia of the very heavy clutch. Ratios were 4, 6.05, 9 and 15.01-to-1 for open cars, and 4.77, 7.17, 10.78 and 17.9-to-1 for closed models.

The spiral-bevel rear axle had fully floating hubs. Four-wheel brakes were used, and the operating gear incorporated a gearbox-driven mechanical servo. This car and the 3-litre were the first Sunbeams to have a slightly vee'd radiator.

The 3-Litre

This famous model captured (and has held) the imagination of enthusiasts to a greater extent than any other Sunbeam product, presumably because it was the only out-and-out sports type produced at the Wolverhampton factory, and was so obviously based on advanced racing-car design. It was not originally intended as a serious production model and the first ("E") sanction was for only 25 cars. The engine was a six-cylinder of 75 by 110 mm. (2,916 c.c. and 20.9 h.p.). The crankcase was an aluminium casting, and the crankshaft ran in eight bearings, one being in front of the timing gears.

The separate block was of cast iron, with fixed head. Two valves per cylinder were inclined at 90 deg. in the hemi-spherical combustion chambers, and were operated by twin o.h.c., through the medium of rocking fingers. The camshafts were driven by a gear-train at the front of the engine, the B.T.H. CE6 magneto being driven by a small separate gear-train between the main camshaft driving gears. The whole gear train, consisting of eleven helical wheels, was driven from the crankshaft through a form of spring drive. This gave rise to a phenomenon known as the "spring-drive period," usually between 1,700 and 2,000 r:p.m., when the backlash in all the helical wheels set up a terrifying clatter, more particularly after a certain amount of wear had taken place.

The valve gear was enclosed in two cast aluminium covers. These camboxes were plain on "E" series cars, and ribbed on all later models. "E" series cars have finned exhaust manifolds, but all later cars have plain ones.

The crankshaft originally fitted was of straight carbon steel, and was unsafe above 4,000 r.p.m. Nickel-chrome cranks were introduced early in the "F" sanction, and as far as possible, all earlier cars were modified.

A brief digression into the subject of Sunbeam engine and chassis numbers may be of interest. The company's policy was to introduce new models when needed and not specifically at the Motor Show. A sanction would be issued for the construction of a certain number of cars of any given model, and these cars were given consecutive unit numbers. As a sanction could run over two or even three years, a suffix letter was added to the unit number to indicate the year of manufacture. Hence "E" cars were built in 1925, "F" cars mainly in 1926, and so on. As engine and chassis manufacture were not in step, it was quite common for, say, an "F" engine to be fitted in a "G" chassis, in which case the chassis number would become, for example, 1400 GF.

Reverting to the 3-litre, on the original "E" cars the water was transferred across the block from the pump via a circular-section pipe cast in between numbers 2 and 3 cylinders. This pipe left insufficient metal between the bores, and caused the block to crack at this point, and on all subsequent cars a pipe of flattened cross-section was used.

Engine data:
Compression ratio 6.4-to-1. Ignition advance 45 deg.  
B.T.H. CE6 magneto. Two Claudel-Hobson AZP carburetters.

The three Sunbeam settings gave identical power curves up to 2,400 r.p.m., at which speed 72 b.h.p. was developed. The "power" setting gave 90 b.h.p. at 3,800 r.p.m., falling to 80 b.h.p. at 4,400 r.p.m.; the "compromise" gave 85 b.h.p. at 3,800 r.p.m., falling to 77 b.h.p. at 4,400 r.p.m.; while the "economy" setting gave 82 b.h.p. at 3,600 r.p.m., 79 at 3,800, and 72 at 4,400. The Claudel-Hobson settings all gave 65 b.h.p. at 2,200 r.p.m. The "power" setting gave 97 b.h.p. at 4,000 r.p.m. The "compromise" gave 93 b.h.p. at 4,000 r.p.m., and the "economy" setting, 88 b.h.p. at 4,000 r.p.m. from which it would appear that "r.p.m., choice" is best for maximum output, but at the expense of petrol coupons. (But it seems open to doubt if the figures claimed for the Claudel-Hobson settings were ever realised, and doubtful in the extreme if the substitution of a 290 for a 280 jet would be worth 7 b.h.p., particularly having regard to the fact that Claudel-Hobson calibrate their jets by flow value and not by size, and the difference is therefore very slight.)

Valve timing: 
I.O.: 8 deg. b.t.d.c.; I.C.: 47 deg. a.b.d.c. (.012 in. tappet clearance; .350 in. lift).

E.O.: 44 deg. b.b.d.c.; E.C.: 18 deg. a.t.d.c. (.015 in. tappet clearance; .356 in. lift).

This very exciting engine was fitted into a chassis which could (and did) carry an elegant town carriage body. The wheelbase was 10 ft. 10½ in., the track 4 ft. 7 in., and the layout the normal Sunbeam one of a frame of channel-section members, sharply kicked up over the rear axle, with asymmetrical semi-elliptic front springs and cantilever rears, all damped by Haxtfords. The "E" series frames all fractured at the front spring shackle bracket, and all later frames were reinforced. It is a pity that this advanced engine was not seen in a chassis better suited to it; nevertheless, maximum speed was in the order of 85 to 90 m.p.h.

The single-plate clutch and four-speed gearbox were unit-mounted, and ratios were 4.5, 6.0, 7.43 and 14.82-to-1, with 10.65-to-1 reverse. Torque-tube transmission was employed, to a ¾-floating rear axle. Cycle-type mudguards, in conjunction with the tall, narrow, V'ed radiator and narrow body imparted a very rakish appearance.

The standard bodywork was an open four-seater with very sporting lines, which sold for £1,125. Also available in 1926 was a four-door, six-light Weymann saloon.

The blown version of this car appeared in 1928 and will be described under that year.

Phase IV
Design Stabilisation

1927

The drawing office must have been very busy during 1926, as three new models appeared in the 1927 programme. The range comprised: a new Sixteen "six" to replace the "14/40"; a new Twenty to replace the "20,60"; an additional model, the Twenty-five; the 3-litre and the Thirty straight-eight were continued with minor changes; and the L.W.B. Thirty, also little changed, was renamed the Thirty-five.

To dismiss the last three models in a few words, the 3-litre tyre size became 31 by 5.25 in. instead of 820 by 120; the Thirty had 33 by 6 in. tyres instead of 895 by 135, and the Thirty-five had 35 by 6.75 in.

The new Sixteen had a six-cylinder, four-bearing engine of 67.5 by 95 mm. (2,040 c.c. and 16.95 h.p.). This engine was originally laid out with 65.5-mm. bore, and was to be known as the "14/60." Presumably the performance did not come up to expectations, and the extra 2-mm. bore was allowed on production cars.

The block and crankcase was a monobloc iron casting, with the sump joint on the centreline of the crankshaft, which ran in four white metal bearings and had a vibration damper at the front end. The timing gears were helical spur wheels, the camshaft wheel being of "Fabroil." The valve gear consisted of barrel tappets, tubular push-rods and rockers, and double springs were used.

The aluminium pistons carried three compression rings and a scraper, and the hollow gudgeon-pins were clamped in the H-section rods. The detail layout was typically Sunbeam, with, the manifolds on the off side, and the auxiliaries arranged along the near side. The oil pump was fitted in the front end of the sump, and was driven by a helical gear from the crankshaft timing wheel.

The carburetter was a Claudel-Hobson V.36, and Delco-Remy coil ignition was adopted. The compression ratio was 5.7-to-1, and the engine gave 44 b.h.p. at 4,000 r.p.m., and 89 lb.-ft. of torque at 2,300 r.p.m.

Valve timing was: —
I.O.: 8 deg. b.t.d.c.; I.C.: 62 deg. a.b.d.c. 
E.I.: 49 deg. b.b.d.c.; E.C.: 11 deg. a.t.d.c.

The drive went via a unit-mounted single-plate clutch and four-speed box, which gave the rather peculiar ratios of 5.3, 8.72, 12.12 and 20.94-to-1, and reverse 15.76-to-1. The gearbox was very neat, with the selector rods at the side to reduce height.

The chassis was normal Sunbeam of 10 ft. 3 3/8 in. wheelbase and 4 ft. 7 in. track. Bolt-on steel artillery wheels carried 4¾ in.-21 in. tyres.

The new Twenty engine was also a four-bearing "six," and followed closely the design of the smaller car. Cylinder dimensions were 75 by 110 (2,916 c.c. and 20.9 h.p.), the same as the 3-litre, but this purely touring engine had a detachable head and push-rod valve gear. The valve timing was not so conservative (almost Fascist!) as most bread-and-butter Sunbeams, and gave 35 deg. of overlap. The figures were:  —

I.O.: 12 deg. b.t.d.c.; I.C.: 56 deg. a.b.d.c.

E.O.: 45 deg. b.b.d.c.; E.C.: 23 deg. a.t.d.c.

Compression ratio was 5.5-to-1 and peak power was in the region of 55 b.h.p. at 3,600 r.p.m., although this model was sometimes referred to as the "20/70."

Incidentally, Sunbeam nomenclature bore only superficial resemblance to Treasury rating, the Twenty, for example, was at various times rated at. 20.9, 23.8, 18.2 and 19.8 h.p.!

This new Twenty engine had a Claudel-Hobson V.42 carburetter and a B.T.H. CE6 magneto, and was mounted in unit with a single-plate clutch and four-speed gearbox, the gear-change being on the right-hand side as on all models up to the 1934 Show. The ratios were more normally spaced than on the Sixteen, being 4.7, 7.9, 12.9 and 18.8-to-1, with 16.54-to-1 reverse.

This chassis again followed normal practice, and had a wheelbase of 10 ft. 4½. in., a track of 4 ft. 7 in. and the wire wheels were shod with 31 in. by 5.25 in. tyres.

The design of the Twenty-five engine perpetuated the earlier features of an aluminium crankcase with a separate cast iron block. Bore and stroke were 80 by 120 mm. (3,617 c.c. and 23.8 h.p.), and power output was 72 b.h.p. at 2,900 r.p.m. The 65-mm. dia. crankshaft ran in seven bearings, and drove the camshaft by silent chain. The push-rod valve gear was unremarkable, as was the valve timing of: —

I.O. at t.d.c.; I.C.: 50 deg. a.b.d.c.
E.O.: 40 deg. b.b.d.c.; E.C.: 15 deg. a.t.d.c.

Ignition was by B.T.H. CE6 magneto, and mixture was supplied by a Claudel-Hobson AZP.1 carburetter. The unit-mounted clutch and gearbox gave ratios of 4.5, 6.08, 12.4 and 18.0-to-1 for open cars, while reverse was 12.6-to-1. The long-wheelbase chassis for closed cars had a 4.73-to-1 axle ratio. Tyres were 33 by 6 in. The chassis was a scaled-up version of the normal layout, and was supplied in two lengths : 10 ft. 11½ in. for open cars and 11 ft. 5½ in. for closed types. Track was 4 ft. 9 in.