Sunday, 23 February 2014
Bentley 3 Litre
It was, he claimed, “one feature that may be described as unique… How many sporting cars will do seventy miles an hour in second gear?” His test car, moreover, had the five-jet water-jacketed Smith-Bentley carburetter, the 45BVS, used up till 1923, not the regular Speed Model’s two sloper SU G5s. Perhaps a 3 Litre Speed Model person can put us right.
The Complete Bentley (Amazon e-book - £12.31). This first Brooklands Gazette of July 1924 gave the price of a 3 Litre with 4-seat body as £1,125 and with two seats £1,100. My research was based on contemporary advertisements and other accounts. I gave the Red Label Speed Model a couple of decimals’ difference in the top gear ratio. You could have any colour you liked on the badges but speed models were all red. “Open Throttle” discovered the “system of dual controlled magnetos” but surprisingly doesn’t seem to have counted the spark plugs. He gives the weight at 19½cwt although that was for the chassis only. Bodywork added 5-6cwt. I think I prefer Motor Sport’s later practice of initialling contributors, such as WB and DSJ.
1924-1929 3 Litre RED LABEL SPEED MODEL
Essentially a development of the TT Replica, Speed Models brought in four wheel brakes, and twin SU carburettors. WO maintained that hydraulic brakes had been tried on EXP2, but production cars had a mechanical system based on Perrot principles, which had a shaft with sliding universal joints. The front axle section was increased to take the strain, and instead of cast iron linings as used in the rear drums, all eight brake shoes had fabric linings. The handbrake operated an additional set of shoes and a single adjustment beneath the floor took up lining wear on all four wheels. There was no servo, but WO and FT Burgess developed and patented a mechanical compensator used subsequently in Bentleys up to the 8 Litre. There were several stages of Perrot-Bentley brakes, improvements having been tried out on Burgess’s experimental car ME 2431, that was doing effective duty as EXP4. The stage 1.1 Perrots ran to 1926, stage 2, which pinned the sliding keys, to 1929. There were gearbox developments and a larger sump as well as a gradual thickening of the chassis frame from 0.144in (3.7mm) to 0.156in (3.96mm), and in 1928 0.188in (4.78mm). Chassis flexure was problematical. LJK Setright: “(WO) carried over to his cars the notions of scale he acquired in railway locomotive workshops. So far as his chassis were concerned, the effect was almost always disastrous; everything about them was of heroic dimensions and villainous proportions, the outcome being an aggregation of components that was grotesquely heavy without being particularly stiff. Indeed the main chassis rails, though of very thick channel section, were only 4in (10.2cm) deep and their inadequate beam stiffness made it necessary for supplementary trusses to be bolted beneath, an arrangement which improved matters in bending but did nothing to improve the torsional stiffness of the chassis.” The reinforcements were struts and stiffeners below the main chassis members giving the effect of a deeper beam section. The radiator header tank was enlarged, making the domed shell 1in (2.5cm) taller and adding dignity to the prow. In 1926 steel rocker arms were replaced with duralumin even though they proved fragile at Brooklands in 1927.
BODY various coachbuilt; chassis weight 20cwt (1016kg); 1925 23cwt (1168.4kg); maximum with body 26cwt (1320.8kg) to 28cwt (1422.4kg)
ENGINE 4-cylinders, in-line; front; 80mm x 149mm, 2996cc; compr 5.6:1, 6.1:1; 85bhp (63.39kW) @ 3500rpm; 28.4bhp (21.18kW)/l; RAC rating 15.9HP
ENGINE STRUCTURE 4-valves, double springs; hollow overhead camshaft gear-driven from front; cast-iron non-detachable cylinder head, cast iron cylinders; aluminium crankcase; cast aluminium 2.5gal (11.4l) sump with gear-driven pump; long securing studs from block to crankcase; two sloper SU G5 carburettors; 2 spark plugs per cylinder; two ML CG4 later some RG4 magnetos, Autovac fuel system; 5-bearing Laystall forged steel crankshaft; water-cooled, L8 hourglass or BHB split skirt aluminium pistons.
TRANSMISSION rear wheel drive; Ferodo-lined 42.25in (107.3cm) cone clutch; separate 4-speed A-type gearbox, or C-type on Speed Models; right hand change; one-piece plunger joint propeller shaft; spiral bevel final drive 3.78, or 3.53:1
CHASSIS pressed 35ton steel channel section frame, 4 riveted cross members; half-elliptic leaf springs (different leaves according to body weight) suspension; Hartford, Duplex friction dampers; 15.75in (40cm) drum brakes with Bentley-Perrot shafts to front; worm and wheel steering; 11gal (50l) fuel tank with 2gal (9l) reserve; Rudge-Whitworth centre lock wire wheels, 820x120 tyres. Dunlop after 1926
DIMENSIONS wheelbase 117.5in (298.4cm); track 56in (142.2cm); length 159in 403.8cm); width 68.5in (174cm); ground clearance 7.25in (18.4cm); turning circle short right 46ft (14m) left 42ft (12.8m).
PERFORMANCE maximum speed, 86mph (138.1kph); 24.3mph 39kph app @ 1000rpm;
0-60mph (96kph) 40sec; fuel consumption 20mpg (14.12l/100km)-25mpg (11.3l/100km).
PRICE chassis only, £1050, 1924 £925; complete car (mostly VDP) £1275-£1475; 1924 £1125-£1350 PRODUCTION 513
FROM THE BROOKLANDS GAZETTE, July 1924
THE sporting car, as a class, has characteristically more distinction than that possessed by touring types. Being essentially out of the ordinary, and representing the result of concentration upon a design intended to emphasise particular motoring qualities, the sporting car usually has quite an individuality of its own. Some sporting cars, of course, are much more conventional than others; whilst there are those which seem to stand quite apart from orthodox standards.
In the latter category one may place the three-litre Speed Model Bentley. This car embodies all the qualities which one has come to consider essential in a sporting car. In addition, it has features and characteristics quite its own. A brief review of the chassis reveals at once how interesting a proposition the Speed Model Bentley is, and this opinion is vastly enhanced when one takes the car for a trial on the road.
The engine is a four-cylinder monobloc of 2,996 cc. capacity and 15.9 h.p. on the R.A.C. rating. Its design has much originality, which has been well justified by the results obtained. There are two inlet and two exhaust valves in each cylinder, arranged in the head and operated by a totally enclosed overhead camshaft and rockers, running in oil. Both crankshaft and camshaft are carried in five bearings. The pistons are of aluminium, designed for high compression service. Cooling is by pump circulation controlled by an automatic thermostat. Ignition on a sporting car is, of course, a factor demanding the most careful attention. One usually has to “drive on the spark” more than is requisite on a touring car, and if one desires to obtain really the best running from the Speed Model Bentley one makes no exception to this rule with it. On this car one finds two M.L. high-tension magnetos, having a synchronised firing point control. The system of dual controlled magnetos enables one to obtain particularly effective ignition. Lubrication is by pressure to the main bearings and big ends, and by splash to the pistons and gudgeon pins. There is a pressure lead from the main oil supply to the hollow crankshaft, through which the camshaft bearings, cams and valve rockers are lubricated.
Carburation is by a five-jet water-jacketed Smith-Bentley carburetter. A notable point is that a petrol consumption of 25 m.p.g. at 30 m.p.h, is guaranteed. The speed model Bentley, considering its wide capabilities, is not under any condition excessive in fuel consumption. The clutch is of the inverted cone type, lined with Ferodo. It has compensated withdrawal mechanism automatically lubricated, and there is a special automatic lubricator for the clutch spigot. The four-speed gear-box gives ratios in the forward speeds of 9.35 to 1, 3 78 to 1, 4.72 to 1, and 3.53 to 1.
It is operated by a simple right-hand gate change carried on an extension of the box. The frame of the chassis is of particularly strong construction, and does not rely on the engine or gearbox for part of its bracing. Double Hartford shock absorbers are fitted to the back axle and single to the front. There are oil lubricated Wefco gaiters on all springs. Steering is by worm and wheel.
In a car of such advanced design as the Bentley, one naturally expects to find front wheel brakes, and the system of fully compensated internal expanding brakes operating on all four wheels and controlled by pedal is very effective. The hand brake operates direct on the rear wheels. Wear on the four wheel brakes can be taken up by a single adjustment.
The tank holds eleven gallons of petrol, and a two-way tap near the filling cap gives access to a reserve supply of two gallons. The cardan shaft is hollow and is loaded with oil through a plug, this reservoir providing an oil supply for the back universal joint. Chassis lubrication is by oil, supplied from an oil-gun through screwed oil plugs. The only grease cup on the chassis situated on the water pump. After the chassis has been lubricated it can be run for three months of normal mileage without further lubrication, apart, of course, from the engine’s requirements.
The wheelbase of the sporting Bentley is 9 ft. 9½ins., and the wheel track 4 ft. 8ins. The weight of the chassis is 19½cwts., and it runs on 820 x 120 m.m. tyres. The annual tax is £16.
From the foregoing it will be appreciated that the Speed Model Bentley is a particularly interesting car. Our road experiences with this model, although not at the moment as extensive as we should like, have convinced us that this car must possess a fascination for every sporting motorist.
The sporting Bentley is naturally a fast car. But that is by no means the sum total of its outstanding attraction. Very few sporting cars arc really docile in control, many are not at all comfortable to ride in. The Speed Model Bentley is a happy exception to this too prevalent rule. We drove the Bentley quite comfortably on top gear at an exceptionally low speed, and found it very docile in traffic and those places wherein “sporting” characteristics are not over appreciated. Owing to its high gear range one must, of course, remember that the four speeds are there to be used. Gearchanging is so easy a matter, however, that one finds not the smallest objection to always starting in first and to a fairly frequent use of the lower ratios in traffic. On each gear the car is instantly responsive its life and acceleration under all conditions being admirable.
There is one feature of the Bentley that may be described as unique, and to this we would give due prominence. How many sporting cars, or cars of any sort, will do seventy miles an hour in second gear? Their number must be very few indeed. The Bentley, however, makes light of this. One can speed up in the ordinary way on the successive gears until one is going along smoothly and comfortably at, say, forty-five miles an hour on top gear. One then changes down direct to second gear, missing third - and things begin to happen. With a slight pressure on the accelerator one can then speed up the Bentley in a few yards to fifty, fifty-five, sixty-five, and seventy quite easily—all on second. The leap forward when the increase of engine revolutions permitted by the sudden change from top to second, is a thing to be experienced to be appreciated. The acceleration is quite remarkable, as remarkable as the fact changing down at forty-five miles an hour itself. The Bentley will hang on to round about the seventy mark on second gear indefinitely, and the change down at speed with a quick double-clutch is not unduly difficult. One can change into top at practically any speed, slow well as fast, and the Bentley will attain the neighbourhood of the eighty mark without much forcing.
Steering of the Bentley is delightfully easy, comparable in its comfort to that experienced on a high quality light car. The four-wheel brakes, operated by pedal, remarkably powerful, and very easy and smooth in operation. Although there is not an over abundance of seating room the Speed Model Bentley is quite comfortable to ride in.
The electrical and other equipment is very complete and the general lay-out of the car very pleasing to those who desire a high quality sporting vehicle which is quite
practicable for ordinary touring and exceptionally attractive amongst sporting designs for town and general use.
The price of the Speed Model Bentley with four seater body is £1,125 and with two-seater body £1,100, purchasers being afforded the option of choosing the colour of body and upholstery. The manufacturers are Messrs. Bentley Motors, Ltd., 3, Hanover Court, Hanover Street, London, W.1. The extensive Bentley factories are at Cricklewood. London, N.W. 2.
Interest in the Bentley is naturally enhanced by this car’s splendid victory in the French Grand Prix d’Endurance last month. The Bentley was the only British car amongst some forty competitors, and its outstanding performance throughout the race provided a notable tribute to British engineering in general, and to Bentley design and workmanship in particular Magnificently driven by Duff and Clement, the Bentley maintained a thrilling struggle with some of the best representatives of French automobile science throughout the twenty-four hours that the race occupied. This event is indeed appropriately named, a trial of endurance, for it is difficult to imagine a more exacting test under road conditions than this gruelling struggle of speed throughout a day and a night.