Jaguar History - Jaguar XK120
The Jaguar XK120 that was unveiled at the London Motor Show in 1948 was the sports car that had everything: a roadster body more beautiful than anything even Jaguar had produced before; an immensely strong chassis that had taken years to develop; and an engine so sophisticated that it looked as though it should have graced a Grand Prix racer rather than a sports car costing only £998! This was not only the first pure-bred Jaguar engine, it was also the world's first mass-production engine with twin overhead camshafts and hemispherical combustion chambers. Such technical sophistication had only been seen before in racing cars costing a great deal of money and produced only in very small quantities. Lyons, who was the inspiration behind the engine, gambled once more on its staying in production for so long that the tooling and development costs would amount to only a tiny sum on each engine, But even he could not have guessed that the XK unit would be so successful that it would still be powering Jaguars into the 1980s!
When this unit was still in the design stage during the war-time fire- watching sessions, even engineers as experienced and adventurous as Heynes, Hassan, Baily and Harry Mundy doubted whether it would be possible to produce a twin overhead camshaft engine for a passenger car. They recognized the advantages of such a layout in that it produced tremendous power, but pointed out that it carried penalties: these engines tended to be very noisy because long chains or trains of gears were needed to drive the camshafts; they were difficult to make, which inevitably meant that they cost more, and were potentially less reliable; and they were far from easy to service. But Lyons would not settle for second best and insisted that he must have a 'twin cam'; what is more, it also had to look good! Once they had expressed their reservations, Heynes, Hassan, Baily and Mundy worked with a will that resulted in the sensational six-cylinder in-line XK unit that produced no less than 160 bhp from 3442 cc. They had the assistance of Harry Weslake, who was to help extract even more power from the engine as time went on. With bores of 83 mm, the XK engine had a relatively long stroke of 106 mm, which gave it impressive torque. Its crankshaft ran in seven main bearings; this meant that the bottom of the engine was extremely strong, which it had to be to transmit the power produced by the top end. The cylinder block was cast in iron by Leyland Motors-the British truck firm that would much later figure prominently in Jaguar history and the head made from alloy, which saved weight and dispersed heat more efficiently. At first the engine was produced in a relatively mild form of tune because it was feared that, had a more radical stage of tune been adopted by using higher-lift cams, inexperienced mechanics might damage the vital valve gear during the decarbonization process, so common in those days. However, the quality of fuel improved and 'decoking' became a relative rarity, and it was found that the average mechanic was so proud to work on such a magnificent engine that he did not 'mess it up', In any case, the XK engine's 160 bhp was enough to propel the 1320 kg (2912Ib) car at more than 190 km/h ( 120 mph), hence the designation XK120.
A rather 'graunchy', but very reliable Moss four-speed manual gearbox was used in a shortened version of the Mark V saloon's ladder-design chassis. This used conventional half-elliptic leaf-spring rear suspension with a live axle, and Heynes's new independent front suspension, which employed wishbones and torsion bars parallel to the chassis sides. A feature of this front suspension was the brilliantly simple ball joints used to locate the stub axle carriers. Steering was a recirculating-ball type and so arranged that it could be set on either the right-or the left-hand side to cater for export markets from the start.
The XK120 in production
At first the XK120 had an aluminium two-seater roadster body, built in the old manner on an ash frame because Lyons did not envisage making many of these cars. He saw them principally as a mobile test bed for the engine and an advertisement for his planned Mark VII saloon, which would use the same unit in the longer Mark V chassis. The great expense of assembling the giant presses and tools needed for all-steel body construction could be justified only if a large number of cars was to be produced. As it happened, there was such a demand for the car that he had to do just that, although it took until 1950 to tool up for the first all- steel XK120. The demand had been set off, first, by the car's spectacular appearance and incredibly low price-there is some evidence that Lyons initially saw it as a loss leader-and, secondly, by a demonstration for the doubting Thomases that it really was capable of the performance claimed when test driver 'Soapy' Sutton managed 213.4 km/h (132.6 mph) with a mildly modified version before astonished journalists on the Jabbeke motorway in Belgium in May 1949. Only a V12 Ferrari costing four times as much and available only to selected racing teams could match this. So Jaguar, who had planned to spend the year making Mark Vs and preparing for production of the Mark VII, found itself with a bulging order book for XK120s.
Competition successes for the XK120
The first customer cars-mostly for export-left Foleshill in July 1949, a month before three were entered in the new Silverstone Production Car Race. It was Britain's first big motor race since the war in which production cars could be compared, and two of the XKs, driven by Leslie Johnson and Peter Walker, left the field standing. Johnson, who won at Silverstone, went on to perform impressively in America before receiving a new works-supported XK120 in company with Walker, Wisdom, veteran Italian racing driver Clemente Biondetti, and rallyman lan Appleyard, whose successes with an SS100 included a Coupe des Alpes in the Alpine Rally. Appleyard had special connections with the factory because, apart from being a Jaguar dealer, his crew consisted of his wife, Pat, who happened to be Lyons's daughter! And their car, registered NUB 120, was to become one of the most successful competition Jaguars.
Johnson spearheaded Jaguar's assault on the classic Le Mans 24-hour race in 1950 and took his near-standard car up to third place, leaving many outright racing sports cars trailing, until failing brakes led to an overstrained clutch and eventual retirement. Many similar cars suffered from brake trouble in those days because of the development of all- enveloping coachwork. These bodies, which were better streamlined than the old-fashioned types used on models such as the SS100, meant that cars were capable of higher speeds, The result was that the drum brakes suffered badly at the limit of their performance, as they had to stop the cars from far higher speeds and, because of the better streamlining, without the benefit of such a good flow of cooling air. This problem was made worse by a reduction in wheel sizes to take modern tyres, which meant that brake drums of smaller diameter had to be used to fit inside the wheels, It was a problem that was not really solved until the introduction of disc brakes, pioneered on competition Jaguars. Despite the retirement of Johnson's XK120 in the all-important Le Mans race, enthusiasts everywhere were extremely impressed by its showing against far more specialized machinery that could not be bought by ordinary people. And Heynes was convinced that, with a special competition version of the XK120, it would be possible to win at Le Mans. Lyons agreed and authorized the building of the C (for Competition) type, which went on in 1951 to the first of Jaguar's five victories at Le Mans, and is described in the 'Glory Years' chapter.
Meanwhile XK120s continued to win races all over the world and make up most of the fields in international rallies. By far the most successful XK120 rally drivers were the Appleyards with NUB 120, which they used to win the Alpine Rally (1950, 1951, 1952) and the Tulip Rally (1951) and many others in a life that extended to more than 100,000 miles!
In America, world champion-to-be PhiI Hill bored out an XK120's cylinder block to 3.8 litres (which was to become a significant capacity in Jaguar history) and won numerous events; in Britain, the greatest driver never to win a world championship, Stirling Moss, made his name in the big time with one of the semi-works XK120s. Moss was offered the car in 1950 when Wisdom opted for an official works drive in a Jowett Jupiter in Britain's premier road race, the Tourist Trophy, held on Ulster's Dundrod circuit. Moss overtook Johnson to win in atrocious conditions and so impressed Lyons that he was signed to drive for Jaguar when the company ran a full works team of C types the following year. It was an excellent birthday present for Moss: he was to be 21 next day! He also made mincemeat of the opposition with an XK120 in the 1951 Silverstone Production Car Race.
Other drivers enjoyed notable success with XK120s, particularly the Belgians Jacques Ickx (whose son became a Grand Prix star) and Johnny Claes who won the 1951 Liege-Rome-Liege rally-in reality the world's roughest road race; former Spitfire pilot Duncan Hamilton; and Sir James Scott-Douglas, who helped start the glorious Scottish team, the Ecurie Ecosse.
The XK120 fixed-head coupe
As these stalwarts raced on their alloy-bodied XK120s, steel-bodied cars, which weighed about 25 kg (56Ib) more, but looked almost exactly the same, had been in production since April 1950. Production of the Mark VII saloon finally started in October 1950, leaving Jaguar's staff free to work on a fixed-head version of the XK120, which was introduced in March 1951. It met the demand for a car as civilized as the Mark VII saloon without sacrificing the performance of the sports car. This new coupe was like an XK120 roadster (to use the American description which has now become universal; Jaguar preferred to call it a super sports) with an attractive steel top, the lines of which bore a close resemblance to those of the Mark VII. Wind-up windows replaced the roadster's sidescreens, the doors were fitted with exterior handles and the interior upholstered like the saloon, rather than the far more spartan-but lighter-roadster. Ventilation had received special attention, with quarter lights front and rear, following complaints about too much heat in the cockpit from people using the cars in hot climates. A heater was also fitted as standard following complaints from people living in cold climates about too little heat in the cockpit! Wire wheels-like those used on an increasing number of competition XK120s to assist brake cooling and fast wheel changing-were offered as an option. When these wheels were fitted to either the roadster or the fixed-head coupe, the rear spats had to be left off because of the protruding knock-off hub spinners.
Soon after, Jaguar provided more options in the form of tuning equipment for customers who wanted to use their XK120s (and Mark VIIs) in competition. These consisted chiefly of higher-lift camshafts, higher compression pistons, larger carburettors, stiffer springs and thicker brake pads; they were based on well-tried items used on the C type. These modifications could boost the engine's power to 190 bhp.
Demand for the XK120 and the Mark VII was so great that Jaguar was again faced with the old problem: the factory was not big enough. So Lyons started searching for new premises once more and managed to acquire a modern factory used by Daimler to make cars and buses. Daimler had made armoured cars there during the war, but its needs were contracting and in 1951 the firm decided to centralize its operation on the main works at Radford, Coventry. Jaguar was happy to move into the million square feet at Browns Lane, Allesley, on the outskirts of Coventry, which is still the company's home.
Meanwhile, the fixed-head coupe, which was not normally used in top--line racing because it was heavier than the roadster-although it found favour in winter rallies-was publicized in 1952 by a run at the Montlhery track near Paris during which Johnson, Moss, Jack Fairman and Bert Hadley averaged 161.43 km/h (100.31 mph) for seven days and nights to cover 27, I 19 kilometres (16,851 miles) and take nine international records.
The XKI20 drophead coupe
The company was still recovering from the move to Browns Lane and it was not until April 1953 that a new Jaguar was launched-in this case a drop head coupe version of the XK120. This was more like the fixed-head car than the roadster, with a well-tailored folding hood replacing the steel roof. The roadster retained its spartan trim and the V-shaped windscreen that protected its occupants so well from the elements, whether the skimpy lightweight hood was up or stowed away: it was considered normal in those days to drive a roadster with the hood off in almost any weather.
The drophead coupe, however, was intended to be driven with the hood down only when the weather was really good. This was particularly important because the flatter, fixed-head style windscreen needed with the wind-up windows set up air currents that whipped around the back of the occupants' necks: fine on a good day but not so pleasant on a bad one!