by John R. Coombes and John Wyer
Continued from December, 1949 issue.
The “six” model range was continued almost without change for 1928. The wheelbase of the Sixteen was increased to 10 ft. 6¼ in., and was therefore 1¾ in. longer than the Twenty. The axle ratio was lowered In 5.5-to-1, and the Twenty also had the lowered ratio of 5-to-1.
The 3-litre was somewhat detuned, the compression ratio being reduced to 6-to-1 with 51 deg. of ignition advance. Dewandre servo braking was adopted. The Weymann saloon body on this chassis had by now become a very handsome four-door, four-light affair, instead of the rather strange six-light model originally announced.
The Twenty-five was also given Dewandre assistance, but the two straight-eights continued to rely on the gearbox-driven mechanical servo.
A supercharged version of the was introduced, and six cars of this type were built, including the prototype. All were “K”-sanction cars. The prototype had a Weymann saloon body, the other five being open-bodied.
This model was raced at Phoenix Park by the late Sir Malcolm Campbell in 1920 and by B. O. Davies in 1930, but retired each time.
The engine was largely standard, but the face width of the crankshaft timing wheel and the idler above were doubled to approximately two inches. This idler transmitted upwards and to the off side to the blower drive shaft, which incorporated two Simm’s couplings. The blower was a No. 11 Cozette running at 1,278 times engine speed, and giving rather over 10 lb. sq. in. boost.
The engine developed 138 b h.p. at 3,800 r.p.m., and the clutch, which was standard but with stronger springs, looked somewhat askance at being asked to purvey this fifty per cent. power increase. This was responsible for the 1929 Phoenix Park retirement.
The mounting of the blower left much to be desired, consisting as it did of two metal straps holding the unit into an aluminium cradle. This arrangement permitted the blower to shift, under load reversal, causing the casing to fracture near the outlet port. This was the cause of the car’s retirement on the sixth lap of the 1930 Phoenix Park event. Fuel feed on the blower cars was by two Amal pumps, one on each cambox, instead of the Autovac as on the normally-aspirated models.
The axle ratio was 3.9-to-1, and the cars which were later de-blown retained this high ratio.
The “race” and “practice” cars, registered UK 7145 and HW 7813, respectively, had short, flowing wings, instead of the normal cycle type, which greatly improved the appearance. The “race” car also had a lower bonnet line and a shallower, wider body, which, in conjunction with the standard seating position used, caused the inhabitants to ride on, rather than in the car.
The “race” car also had heavier springs than standard, which were clipped on every leaf, and eared, instead of plain Rudge hub caps.
The range was almost unchanged for this year, excepting that the smaller straight-eight was dropped. The Twenty acquired a Dewandre servo, and all models were fitted with a pedal-operated, centralized chassis lubrication system, the oil tank for which was mounted on the engine side of the dash.
This year the surviving straight-eight ceased to be among those present, and considerable modifications were to be observed throughout the rest of the range. For some time, much agitation had been felt on account of rapid bore wear on most models, and much experimental work had been undertaken in efforts to conquer the trouble. These efforts culminated in the introduction, on all models except the Twenty-five, of the Sunbeam patent bi-metal piston.
This piston was of very interesting design, comprising an aluminium crown, cast complete with gudgeon-pin bosses, and which carried the three compression rings. The skirt was formed from solid drawn steel tube. The gudgeon-pin holes were pierced in this tube, the same operation pressing the surplus metal inwards to form bosses. A scraper ring groove was turned at the bottom, and the inside was machined all over to give a skirt thickness of about 1 mm. The resulting piston was little, if any, heavier than an aluminium one, but while the crown was machined to the large diametrical clearance necessary with light metal, the skirt could be held to a much closer clearance. The gudgeon-pin formed the only connection between head and skirt. This design, though expensive, was successful in reducing oil consumption, piston slap and bore wear.
The bore wear problem was probably largely a result of the small ratio of connecting-rod length to crank radius which was a feature of Sunbeam engines, causing excessive side thrust between piton and cylinder wall.
The 1930 Sixteen engine was largely unchanged, but an entirely new chassis was used. Although the rear axle was still located by a torque-tube, cantilever springs gave place to semi-elliptics shackled at both ends. The gearbox ratios remained as before, but the axle ratio was again lowered, and became 5.6-to-1. The hand-brake lever now operated separate shoes in the rear drums.
The above description also largely covers the Twenty, which, however, had an oil radiator fitted between the front dumb-irons, the idea being to assist the new pistons in the attack on oil consumption and wear. A B.T.H. CED6 dual ignition unit was used, and the Carburetter was a Claudel-Hobson V.36BD pump-type instrument.
The long chassis had a wheelbase of 10 ft. 11 3/8 in. Braking was assisted by Mr. Dewandre, and the axle ratio was lowered to 5.1-to-1.
Major changes on the Twenty-five consisted of the use of a Stromberg UX2 carburetter instead of the Claudel-Hobson previously fitted, and dual ignition as on the Twenty.
The 3-litre was awarded a new wide-ratio box, giving 4.5, 6.46, 9.2 and 14.26-to-1, with a 12.46-to-1 reverse. It also featured the new pistons and dual ignition.
Incidentally, these rare “L”-sanction 3-litres produced in 1930 had many of the improvements of the supercharged cars, including mechanical pumps for the fuel feed and considerably larger brakes.
The price of the open four-seater was now only £850!
Members of the V.S.C.C. will not be surprised that the 3-litre was dropped from this year’s range. Production of “real” motor cars had ceased!
Turning now to the “lesser breeds,” weights having continued to rise, and axle ratios having been lowered to (or beyond) the limit, engine capacities had to be increased. Thus the Sixteen bored out to 70 mm., making the R.A.C. rating 18.2 h.p., and the swept volume 2,194 c.c. An Amal 30 VP carburetter was fitted.
The chassis design was little changed, except for the adoption of Lockheed brakes, and Magna large-hub wheels. The hand-brake lever operated the rear shoes through a toggle linkage.
The Twenty also was given a larger engine of new design, having six cylinders of 80 by 110 mm. (3,317 c.c. and 20.8 h.p.), with a dry-linered iron block, a seven-bearing crankshaft with 65-mm. diameter journals, coil ignition, a Zenith UP 36 carburetter, and bi-metal pistons carrying five rings. The oil cooler used the previous year was hastily thrown away, having proved so successful in cooling the oil that circulation was almost unnoticeable, and wear problems were worse than before! As a further aid to quick warming-up, hand-operated radiator shutters were introduced as standard.
Petrol feed was by an A.C. pump, instead of by an Autovac as used on other Sunbeam models.
A “Twin-top,” silent-third gearbox gave ratios of 5.1, 6.96, 10.26 and 18.55-to-1, with a 22.95-to-1 reverse, and tyres were 6.00-20 in.
The Twenty-five continued much as before with its 80 by 120-mm. engine. We therefore see the unusual sight of two models in the same range of the same bore diameter, one called a “Twenty,” and the other a “Twenty-five,” neither of which manes gave the true rating of 23.8 h.p.!
The Twenty-five was given bi-metal pistons with four rings.
The three-model range of Sixteen, Twenty and Twenty-five was continued for this year, with slight modifications. Thus the Sixteen was fitted with a “Twin-top ” gearbox giving ratios of 5.6, 8.2, 13.2 and 20.38-to-1, and 25.2-to-1 reverse.
Rapid warming-up was ensured on all models by the adoption of thermostatically-controlled radiator shutters. The Twenty was given Lockheed brakes.
The Twenty-five was dropped from the range, its place being taken by the long wheelbase “Twenty.” The only new model introduced was the 20-h.p. “Speed Model.”
All models now had coil ignition, bi-metal pistons, and A.C. mechanical fuel pumps, which drew petrol via an auxiliary tank on the scuttle. Common chassis features included Lockheed brakes, and silent-third synchromesh gearboxes. The L.W.B. (10 ft. by 11 3/8 in.) Twenty had a twin-top “crash” box, but the synchromesh box was available at £10 extra. The “crash” box was optional on the two smaller models, but there was no equivalent reduction in price!
The new “Speed Model” was introduced to use up the surplus stock of old 20-h.p., 75 by 110 mm., four-bearing engines and gearboxes. The prototype car had a cut-down Sixteen chassis and a 3-litre sports body. For production a new chassis of 10 ft. 0 in. wheelbase and 4 ft. 7 7/8 in. track was developed, and was fitted with a rather queer-looking close-coupled saloon body.
Compression ratio was 6.240-to-1 and various carburation systems were tried during development. To be fashionable a 46-mm. downdraught Zenith carburetter was adopted for production cars, but best power output was obtained with a dual vertical Solex.
Power output was 72 b.h.p. at 3,600 r.p.m., and this is the first time that this engine, which had been known as the “20/70,” had ever given a genuine 70 b.h.p.
The gearbox was a “crash” type (surplus with the engines), and gave ratios of 4.9, 7.13, 10.89 and 19.6-to-1, with reverse at 14,82-to-1. Tyres were 5.25 in.-20 in., and top speed was just on 80 m.p.h.
The 70 by 95-mm. (2,194 c.c.) engine was fitted in the 10 ft. 0 in. wheelbase “Speed Model” chassis and marketed as the new Twenty. The “Speed Model” chassis was unchanged, but was now fitted with a very handsome pillar-less four-door saloon body.
The 80 by 110-mm. (3,317 c.c.) engine was fitted in a new low frame chassis, and was known as the Twenty-five. This car had the dynamo mounted below the radiator, and driven from the front of the crankshaft. A Zenith downdraught carburetter was fitted, and the power developed was 74 b.h.p. at, 3,250 r.p.m.
The frame, of 10 ft. 10 in. wheelbase, was a cruciform braced affair, and semi-elliptic rear springs were used, with an open Hardy-Spicer propeller-shaft. It will be noticed that chassis design had now gone full circle, and returned to the immediate post-war layout!
It is virtually impossible now to avoid the Victorian novelist’s cliché, “came the ‘Dawn.” This was the new small Sunbeam model, a four-cylinder of 72 by 100 mm. (1,627 c.c. and 12.8 h.p.), with push-rod o.h.v. The engine, like the original 1922 14-h.p., had a combined block and crankcase casting of aluminium, but with wet liners instead of dry.
The crankshaft ran in three white metal bearings, and Sunbeam bi-metal pistons were used. The valves were set in line in the cast iron head, and the valve timing was:—
I.O.: 10 deg. b.t.d.c.; I.C.: 50 deg. a.b.d.c.
E.O.: 50 deg. b.b.d.c.; E.C.: 10 deg. a.t.d.c.
Tappet clearances were: inlet .006 in., and exhaust .008 in., in common with all other Sunbeams except the 3-litre.
Coil ignition was adopted in conjunction with 14-mm. plugs. Power output was 49 b.h.p. at 4,200 r.p.m.
A four-speed Wilson preselector box was mounted in unit with the engine, and gave ratios of 5.77, 8.54, 13.1 and 23.08-to-1. Reverse was no less than 32.98-to-1. An open Hardy-Spicer shaft was used, and the axle was located by semi-elliptic rear springs.
The frame was cruciform-braced like the new Twenty-five, but i.f.s. was adopted. A single, low-mounted transverse spring carried the lower ends of the steering heads, the top ends of which were located by radius arms formed from rectangular-section steel tube. These arms gave insufficient “foot” to deal with fore and aft loading, which was looked after, not altogether successfully, by channel section torque arms running back to Silentbloc trunnions halfway along the frame. These torque arms constrained the wheels to move in a fore and aft are, whilst the “parallelogram” layout gave vertical movement. This fact, in conjunction with the very complex loading imposed on the torque arms under various conditions, caused these members to fracture, and many and varied were the schemes of gusseting tried in order to mitigate this evil.
Tyres were 4.75-18 in., and wheelbase and track were 9 ft. 2 in. and 4 ft. 4 in., respectively.
A six-light four-door saloon body with turned-under back panel was the only style listed, at £485.
The “Dawn” represents a departure from accepted Sunbeam practice in a number of interesting particulars, and as it was the only really new design to appear later than 1927 a word of explanation is perhaps not out of place. From 1930, when Hugh Rose left, until 1932, the company had been without a Chief Engineer, and design, such as it was, had been carried on by the drawing office, working along well tried lines. Rose himself, during what was his second term with the company, had been mainly concerned with the Sunbeam commercial vehicle, and had had little influence on passenger car design. In 1932 H. C. M. Stephens rejoined the company, he too having worked under Coatalen in the heyday. His previous appointment had been with Singer, and he brought in his train a number of the Singer designers and draughtsmen. It seems this team who were responsible for the “Dawn.” This was to be Stephens’ only excursion, both the “Speed Model” and the low-frame Twenty-five having been on the drawing hoard before he arrived. He left soon afterwards.
The models announced at the 1934 Show did not have a very long run, as the financial troubles which had beset the company for some time past came to a head at about the turn of the year, a receiver was appointed, and production of cars at the Wolverhampton factory ceased during the early summer of 1935.
The “Dawn” was given a synchromesh gearbox, and all models had remote central gear-levers, for the first time in the firm’s history. The “Dawn” was offered with rather an attractive four-light, swept-tail sports saloon body, and ugly six-light, swept-tail body.
The “Speed Model” was renamed the “Twenty-one Sports,” and was given a new four-light sports saloon body with a large swept boot and very slim screen pillars formed from an extruded alloy section. This model also had a synchromesh gearbox.
A new Twenty engine appeared, and being a six-cylinder of 73 by 110 mm. (2,762 c.c. and 10.8 hp.) was at long last taxed as a “Twenty.” It had a four-bearing crankshaft, and combined cast-iron block and crankcase. In all respects it followed normal Sunbeam practice, with push-rod o.h.v. and coil ignition. Compression ratio was 5.3-to-1 and the engine developed 59 b.h.p. at 3,600 r.p.m.
A single dry-plate clutch and four-speed synchromesh gearbox transmitted the drive to an enclosed propeller-shaft and a spiral-bevel rear axle.
The Twenty-five underwent only minor detail changes.
And so, half way through 1935, a famous name lapsed. Rootes, as the principal creditors, acquired the assets of Sunbeam and the British Talbot Company, while the third member of the group, Talbot of Suresnes, remained independent under the direction of Lago. Perhaps because, of latter years, Talbot had been enjoying a modest financial success, whereas Sunbeam, after carrying the combine for so long, had been showing a loss, when the first attempt was made to revive the name it was under Talbot auspices. This, of course, was the Roesch-designed straight-eight “Thirty” of 80 by 112 mm. (the same dimensions as the then current Talbot 110 by the same designer). This engine was fitted in a large and rigid chassis carrying i.f.s. of modified “Dawn” type, but after being exhibited at the 1936 Motor Show the model was never seen again, and none reached the hands of private owners.
The name then lapsed again, and it really seemed that Rootes were somewhat embarrassed to know what use to make of it. One cannot help feeling that they missed a great opportunity of producing the model which their range lacked, a car of advanced design and genuinely high performance. They had but to apply the principles which Sunbeam had learned ten years earlier in order to anticipate the “XK” Jaguar by more than a decade. But that was expecting too much of the nineteen-thirties. Rootes decided upon the more cautious policy of allying the name Sunbeam to that of Talbot, to cover the range of cars which had just appeared. And so it has remained.
[John R. Coombes, who, like John Wyer and Heal’s 3-litre Sunbeam, is still actively with us, points out that the first Sunbeam to leave the Wolverhampton factory, after the Kaiser War was, of course, a side-valve “sixteen” and not, as we captioned its picture, a “16/40,” which was the later o.h.v. model.—Ed.
See also table on page 33
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