ACTUATOR VALVE WIKI

The Jaguar D-Type, like its predecessor the C-Type, was a factory-built race car. Although it shared the basic straight-6 XK engine design (initially 3.4 litres and uprated to 3.8 litres in the late fifties) with the C-Type, the majority of the car was radically different. Perhaps its most ground-breaking innovation was the introduction of a monocoque chassis, which not only introduced aircraft-style engineering to competition car design, but also an aeronautical understanding of aerodynamic efficiency. The D-Type was introduced purely for competition, but after Jaguar withdrew from racing, the company offered the remaining, unfinished chassis as the roadgoing Jaguar XKSS, by making changes to the racers: adding an extra seat, another door, a full-width windshield and primitive folding top, as concessions to practicality. However, on the evening of 12 February 1957, a fire broke out at the Browns Lane plant destroying nine of the twenty five cars that had already been completed or in semi-completion. Production is thought to have included 53 customer D-Types, 18 factory team cars, and 16 XKSS versions.
The new chassis followed aircraft engineering practice, being manufactured according to monocoque principles. The central tub, within which the driver sat, was formed from sheets of aluminium alloy. To this was attached an aluminium tubing subframe carrying the bonnet, engine, front suspension, and steering assembly. The rear suspension and final drive were mounted directly onto the monocoque itself. Fuel was carried in deformable bags inside cells within the monocoque; another aircraft innovation.[1]

The highly efficient, aerodynamic bodywork was largely the work of Malcolm Sayer, who joined Jaguar following a stint with the Bristol Aeroplane Company during the Second World War. Although he also worked on the C-Type, the limitations of the conventional separate chassis did not allow full expression of his talent. For the D-Type, Sayer insisted on a minimal frontal area. To reduce its height, Haynes and former-Bentley engineer Walter Hassan developed dry sump lubrication for the XK engine. By also canting the engine over by 8° (resulting in the trademark, off-centre bonnet bulge) the reduction in area was achieved. Care was taken to reduce drag caused by the underbody, resulting in an unusually high top speed; for the long Mulsanne Straight at Le Mans, a large vertical stabiliser was mounted behind the driver's head for aerodynamic stability with minimum drag. For the 1955 season, factory cars were fitted with a revised, long-nose version of the bodywork, which increased top speed even further.

Mechanically, many features were shared with the outgoing C-Type. The ground-breaking disc brakes were retained, as was the XK engine. Apart from the new lubrication system, as development progressed during the D-Type's competition life the engine was also revised. 1955 saw the introduction of larger valves, and an asymmetrical cylinder head design within which to accommodate them. The Jaguar D-Type was the second racing car to have Dunlop disk brakes. The Citroën DS, introduced a year later, was the first production car with disk brakes in Europe. The Crosley Hotshot was the first American automobile with disk brakes, in 1949.

Elements of the body shape and many construction details were used in the iconic Jaguar E-Type.
The D-Type was produced by a team, led by Jaguar's race manager Lofty England, who always had at least one eye on the 24 Hours of Le Mans, the most prestigious endurance race of the time. As soon as it was introduced to the racing world in 1954, the D-Type was making its presence felt. For the 1954 24 Hours of Le Mans the new car was expected to perform well, and perhaps even win. However, the cars were hampered by sand in their fuel. After the fault had been diagnosed and the sand removed, the car driven by Duncan Hamilton and Tony Rolt quickly got back on the pace, finishing less than one lap down on the winning Ferrari.

The 1955 car incorporated the new long-nose bodywork, and the engine had been uprated with larger valves. The team again proved strong at Le Mans, and with no sand to worry about they were a good match for the Mercedes-Benz 300 SLR cars who were hotly tipped to win. Sadly the contest was curtailed by one of the worst accidents ever to occur in motorsport: after only three hours of the twenty-four had elapsed, Pierre Levegh's SLR clipped the tail of an Austin-Healey, sending the German machine into the hay-bale barrier. The Mercedes erupted into a flaming ball and sent burning wreckage and debris into the crowd. More than 80 people, including Levegh, were killed, and many more injured. Mercedes withdrew from the race almost immediately, although at the time Juan Manuel Fangio was leading in his SLR, but Jaguar opted to continue. Some blamed Mike Hawthorn for causing the crash as he swerved his D-Type in front of the Healey, setting off the tragic chain of events. Hawthorn and his

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