Specification, Changes and Production Numbers
by Colin Hughes
Rolls-Royce Silver Cloud and Bentley S: 1955 – 1959
By 1950 Rolls-Royce were looking for a new look, initially with a version of the Bentley Mark VI - the Bentley VIII - with the standard steel body moved forward to improve the ride for rear seat passengers, and the engine and radiator also moved forward; and then with a Park Ward saloon similarly meeting this specification. The larger boot Bentley R Type was introduced in 1952 as a stop-gap
The illustration shows the dimensions of the standard body: it did not provide much more interior space than the Mark VI and R Type, but gave considerably more boot space.
The chassis was of welded box-frame sections instead of the open channel chassis of the R Type and Silver Dawn. The engine capacity was increased from 4566 to 4887cc, which was the same capacity as introduced in the later R Type Continental in 1954. Full-length cylinder liners were fitted to overcome the problems with the earlier short liners in the Mk VI and R Type.
However, although the running gear looked much as it had before, the engineers had looked at every aspect of the R Type’s engine and transmission and improved it. Since the new car was to be larger and heavier, it would need more power to produce the same performance, and also more stopping power. While the limit had been reached to which the engine could be bored out, it was given an entirely new aluminium cylinder head with six separate inlet valve ports, replacing the previous head which had shared four ports among six cylinders. There were six exhaust ports also replacing four. All models were fitted with twin horizontal S.U. carburettors and for the first time the Rolls-Royce car shared the same tune as the Bentley variant: the Bentley R-type had had twin SU carburettors, but the Rolls-Royce Silver Dawn only had a single downdraught Zenith. The existing, and very reliable, hypoid-bevel rear axle and final drive assembly were retained, but there were many detail modifications which meant that new and old were not interchangeable. There was also a new ratio of 3.417:1.
Since disc brakes were still in the development stage, the Girling drum brake system was optimised by increasing the lining area in the drums themselves. Twin trailing-shoe front braking was adopted. The brake system was now hydraulic to both front and rear drum brakes, but still operated using the Rolls-Royce mechanical servo, which in turn was made more effective by increasing the speed at which the transmission-driven shaft rotated. Mechanical linkage assistance to the rear brakes was retained to improve feel. In 1956 the master cylinder was duplicated to allow independent operation of one set of shoes on the front brakes while the other cylinder operated the other set of front shoes and the rear brakes; the mechanical linkage to the rear brakes meant that the braking system was fail-safe. The front/ rear braking ratio was 1.36:1.
From the start, the car was only offered with four-speed automatic transmission, although a "Continental" version of the Bentley S was available on introduction of the new range and for this a manual gearbox was initially available.
A publicity shot from HJ Mulliner showing a later style they developed from the fast-back style giving more luggage space and rear headroom.
General Motors had produced the first fully automatic transmission: the Hydramatic, which had been offered as an option in Oldsmobiles in 1940. Rolls-Royce could not afford to develop its own and it assessed the Hydramatic against such competition as existed at the time. Although a mass-produced item, it proved to be extremely well-built, reliable and even cheap and the company placed a long-term contract with General Motors. It had been available as an option in the Silver Dawn/ R Type from 1952 and it continued virtually unchanged in the Silver Cloud. In fact it lasted up to 1968 and the first Silver Shadows.
There was no mechanical difference between the Rolls-Royce and Bentley versions of the car: only the badges, radiator and bonnet were different.
During the four years of the Silver Cloud and S Type there were two major specification changes: air-conditioning and power-assisted steering. Both were introduced as options for the export market in March 1956, and for the home market in October of the same year.
“Refrigeration” - as air conditioning was known at the time – was then a remarkable novelty in the UK, but it had existed in the USA since 1940 and Rolls-Royce had to make up ground to keep their market share. This option came at the considerable cost of £385, which came to £577 when British purchase tax was paid. This may seem insignificant today, but at the time it was almost the cost of a new Morris Minor. However, size proved to be more of a problem than cost and much time and effort was spent in working out how to install it. In the end, a two cylinder compressor was fixed to the front of the engine which was belt driven from the crankshaft, with a condenser mounted ahead of the radiator block immediately behind the grille. The refrigeration unit itself was mounted in the boot area behind the rear seat, along with centrifugal blowers ducting cool air to vents in the cant rails above and behind the passenger doors. The unit was connected to the front end by a system of pipes clipped into the body sills. Later versions had the evaporator mounted at the rear of the off-side front mudguard, feeding cool air to the face. The system was very powerful and delivered a complete change of air every 90 seconds and the engine idle speed was set higher so that the occupants would be kept cool even when the car was stationary.
Power-assisted steering was a joint project between Marles and Rolls-Royce and was introduced as an export item in March 1956 and became generally available later in that year. It proved to be very popular; though it was never to be standardised on normal wheel-based S1 types.
Hydraulic power came from a Hobourn Eaton pump, which was mounted on the front of the engine and belt driven. This operated an actuating cylinder or ram which was fixed to the chassis front cross-member and was attached to one of the forged arms which formed an idler lever in the steering linkage itself, pushing or pulling as directed. If by any chance the belt broke or the hydraulic fluid leaked out, the steering merely reverted to manual, without assistance.
This was introduced in the autumn of 1957 at a time when Rolls-Royce were developing the new Phantom V with a colossal wheelbase of 145 in (3683mm) and the existing longer wheelbase chassis of the Silver Wraith was soon to disappear. The company decided to provide something in between and introduced a longer wheelbase of 127in (3226mm) for the Silver Cloud and at the same time the engine output was slightly increased to allow for a slightly heavier car. The new Bentley Continental had been given larger inlet valves, a raised compression ratio of 8.0:1 and 2.0in choke SU HD8 carburettors and this was standardised on all cars across the range. This marked the final uprating of the 6 cylinder B60 engine and we know from a lecture given by Harry Grylls in 1963 that the final output figure for this engine was 178bhp. Since Rolls-Royce also acknowledged that the final increase was 13% then the figure for the first Silver Cloud must have been around 157bhp.
The difference is very hard to spot from the outside and lies in the fact that there is a rear quarter light built in to the bodywork behind the line of the rear doors. On the standard wheelbase car the window is there, but it is part of the door itself.
In the early 1950’s Rolls-Royce had realised that the 6 cylinder engine would be at the limit of its development by the end of the decade. It would have been possible to redesign the cylinder head and valve arrangements to increase its breathing abilities and it would have been possible to add on 2 more cylinders, but fundamentally the engine was too large, heavy and old-fashioned. The Board approved the research and design of a new V8 engine which could be used in current models and in at least two generations of new models beyond them. They were therefore looking ahead by some 20 to 25 years. In fact the new engine was to continue for more than 40 years.
Although Royce had tried a V8 engine in 1905 and learned a lot, he did not return to it. In engineering terms only two configurations offer perfect dynamic balance and these are a straight six and a 60 degree V12. This meant a lot to Royce who settled on the straight six for the cars, while the Merlin and Griffon aero engines of the 1930’s had a V12 layout. Rolls-Royce had used a V12 layout in the Phantom III engine before the War, but this “all new” approach had caused them problems.
Royce had not been the only one to experiment with a V8 engine. Cadillac had first used one in 1915; but they were not widely adopted until the late 1940’s when a number of manufacturers in the USA developed them. The USA was a very important export market for Rolls-Royce who were obliged to take note of its trends, furthermore the alternative of a V12 would have higher development costs and create service implications. Two V8’s in particular made their mark in the American market after the war. Cadillac, who were strong rivals, launched an overhead valve V8 of 5.4 litres in 1948 which produced 270bhp. Chrysler also developed a V8 of 5.4 litres, which appeared in 1950. It had a hemispherical head layout with opposed valves and centrally mounted spark plugs, and gave a very high power output. While Rolls-Royce used a design based upon the Chrysler hydraulic tappet, their final version of the engine was to differ in certain key respects. Both American engines used cast-iron cylinder blocks and heads, whereas Rolls-Royce used cast aluminium. Furthermore, Rolls-Royce discarded the hemispherical cylinder head and used conventional wedge-profiled combustion chambers.
In September 1959 the new aluminium alloy 6230cc V-8 engine was introduced with hydraulic tappets and two SU carburettors mounted in and above the vee of the cylinder block. Each cylinder head had lines of valves angled inwards 28 degrees towards the vertical, rather than in line with the cylinder bores. The power output was never officially revealed, but it has been estimated at about 200 bhp. One feature is of great significance to anyone maintaining the car. For packaging purposes the exhaust manifolds were above the twin rows of spark plugs, which they masked. This makes it very difficult to remove the plugs and special removable access panels were provided in the inner wheel arches, inboard of the front suspension. Nonetheless, the left side bank of plugs is difficult to locate from above.
The V8 engined cars became the Silver Cloud II and Bentley S2. To accommodate the wider engine, the steering box was moved from the inside to the outside of the chassis frame, with two pinions in the steering drive to maintain the steering wheel centre unchanged: the steering wheel became smaller and closer to the fascia and was more steeply raked. Power-assisted steering was now standard.
Centralised chassis lubrication was abandoned in favour of oiling or greasing points with individual reservoirs needing attention every 10, 000 miles or yearly intervals. The front suspension wishbones had been pressings, but were now replaced with forgings and there was a stiffer front anti-roll bar. The operation of the brake servo was speeded up once again to reduce delays at slow speeds and the front/ rear braking ratio was changed to 1.66:1.
There had been no provision for an air-conditioning unit in the original cars and this had been squeezed into the boot as an afterthought. This was now discarded in favour of a brand new, more complex, but cheaper system which was fitted between the bulkhead panel and the instrument board, with the heat-exchanger in the right wheel arch, shielded from the front wheel. Outside air was drawn in from the grille to the right of the radiator. For recirculation of air and refrigeration purposes there was a grille in the body floor behind the right hand front seat.
This system could supply fresh air, heated air, refrigerated air and mixtures of all three. It also subtly reflected a social change in that the old system supplied much of its air-conditioned output to the rear of the car. The emphasis of the new system was around the front seats, where the owner was now presumed to spend most of his time.
Externally the Rolls-Royce and Bentley versions were virtually identical except for the radiator and the badges on the boot lid and hubs.
In autumn 1962 the production cars were given a facelift and the Silver Cloud III and Bentley S3 were introduced. The most obvious visual feature was the twin headlamp arrangement in what was virtually an unchanged body style. Four headlamps provided more illumination and made it easier for Rolls-Royce to pass the latest North American lighting regulations. Also this layout had been chosen for the next generation Silver Shadow and this provided a convenient way of bridging the visual gap between the old and the new. The side lamps and flashers were combined and mounted in the noses of the front mudguards: the earlier cars had separate side lamps on the top of the mudguards and used the fog lamps also as flashers.
The radiator was lowered by 1.5 inches and the bonnet sloped downwards to suit, thereby improving the driver’s close-to-car vision. A detail seen in some cars nowadays was the addition of a chrome strip on the front mudguards along the swage line above the wheel opening. This was because the mudguard was not a single pressing and was welded at this point: it was easier to fit the chrome strip than to achieve the desired finish to the paint.
Internally, individual front seats became standard and there was some reshaping of the rear seats. The heating/ ventilation system was upgraded, there were extra radio controls and a number of other such details were improved. The engine had a new compression ratio of 9.0:1; the crankshaft was nitride hardened and there was extra power assistance for the steering.
Even the coachbuilt bodies previously reserved for the Bentley Continental became available in Rolls-Royce form; a policy which continued until the introduction of the Bentley Mulsanne Turbo.
Silver Cloud 1955-1959
Silver Cloud II 1959-1962
Silver Cloud III 1962-1965