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The Jaguar XK dual overhead camshaft (DOHC) inline 6-cylinder engine was introduced in 1949 and continued in manufacture until 1992. It was produced in five displacements for Jaguar passenger cars, with other sizes being made by Jaguar and privateers for racing. In contrast with contemporary BMW and Mercedes engines, the original XK engine was relatively unstressed and produced high torque thanks to its more advanced valve and head configuration. ==Early development== Prior to World War II, SS Cars (as Jaguar was then known) used engines produced by the Standard Motor Company; a 1.5-litre 4-cylinder and two 6-cylinder engines of 2.5 and 3.5 litres. Sir William Lyons and his engine designers; William Heynes (Chief Engineer), Walter Hassan and Claude Baily, are widely reported to have discussed a new range of engines to replace the pre-war Standard based units whilst fire-watching on the roof of the SS factory in Swallow Road, Coventry,〔"Sir William Lyons - The Official Biography" by Philip Porter & Paul Skilleter, Haynes Publishing, ISBN 978-0-85733-106-9〕 during German World War II bombing raids and to have developed prototype engines immediately after the war. In fact, Jeff Daniels〔Daniels, Jeff. ''Jaguar - The Engineering Story'', Haynes, ISBN 1-84425-030-X〕 has demonstrated that Jaguar’s wartime engine developments went far beyond mere discussion and design, extending to the construction and testing of several prototype engines from as early as 1943. The initial aim was to produce a series of engines of higher than normal output that would be able to stay ahead of the competition without revision for many years and which Sir William insisted also had to "look good". In 1942-43, a range of configurations was considered and it was concluded that, for good breathing and high bmep, the new engines would need vee-opposed valves operating in hemispherical combustion chambers. Two configurations of this type were selected for comparison in 1943 and the prototypes named "XG" and "XF". The XG 4-cylinder of 1,776 cc, first tested in October 1943, was based on the 1.5-litre Standard block and used its single cam-in-block to operate the opposed valves via a complicated crossover pushrod arrangement, similar to that of the pre-war BMW 328. The XF 4-cylinder of 1,732 cc used the now familiar dual overhead cam (DOHC) configuration and was first tested in November 1944. The XG was found to suffer from excessive pushrod and rocker noise and gas flow figures through its vertical valve ports did not equal those of the horizontal ports on the XF. Therefore, from these two options, the DOHC XF layout was selected. 4-cyl engine development progressed as follows: * XG Pushrod engine 73 x 106 x 4 1776cc May to Nov 1944 * XF 75 x 98 x 4 1732cc Nov 1944 to Jun 1945 * XK1 (first of Haynes’ 4 x XJs) 76.25 x 98 x 4 1790cc Oct 1945 to Nov 1946 * XK2 76.25 x 98 x 4 1790cc Feb to Sep 1946 * XK3 76.25 x 98 x 4 1790cc Dec 1946 to Feb 1947 * XK4 76.25 x 98 x 4 1790cc Nov 1946 to Dec 1947 * Gardner Engine (used in record-breaking MG car) 1970cc 1948 * XK Number 1 3-bearing crank 1970cc 1949-1952 * XK Number 2 3-bearing crank 1970cc 1950-1952 * XK 5-bearing crank 1970cc 1953 By September 1947 a 3.2-litre 6-cylinder version had been produced, called the "XJ 6-cylinder", which was intended to replace both Standard-based 6-cylinder units. Testing showed the need for higher torque at low speeds than this engine could produce and hence it was 'stroked' to form the "XK 6-cylinder" which, with its initial capacity of 3,442 cc, was settled upon for production in 1947-48. This engine first powered the Jaguar XK120, followed by the Jaguar Mark VII and a number of other Jaguar models in subsequent years. The XG prototype soldiered on as a component testbed until 1948. There also existed an "XK 4-cylinder" of 1,790 cc, also first tested in October 1945 and remaining under development alongside the XK 6-cylinder units. At the time of William Heynes' paper presented to the IMechE in February 1953,〔Heynes, W M. ''The Jaguar Engine'', a paper presented to the Institution of Mechanical Engineers on 27 February 1953〕 the XK 4-cylinder was still referred to as being under development. It was only finally dropped as a possible production engine later in 1953, by which time it had been realised that Jaguar's image in the market had moved beyond the need for a replacement for the old 1.5-litre Standard 4-cylinder unit. Because the 6-cylinder XK prototypes were found to be so much more refined than the 4-cylinder versions, in 1951 a 1,986 cc 6-cylinder version of the XK 6-cylinder was built to see if it would suffice as a smaller scale engine. By 1954 this had grown to 2,483 cc and it was this short-block version of the XK 6-cylinder that was fitted to the new compact Jaguar 2.4-litre (retrospectively known as the Mark 1) released in that year. None of the 4-cylinder prototypes ever advanced to production. There are some misleading claims of an intervening "XJ" 4-cyl prototype but it seems the only person who referred to them as such was William Haynes in a paper presented to the IMechE in 1953. Haynes stated there were many 4-cyl variants following the XF but it was he alone who loosely grouped them as XJ. The last mention of XF was in July 1945 and the first mention of XK (XK1) was in October of the same year. This doesn’t give much room for a series of XJ engines.There are no mentions of XJ in the archive (other than in Heynes’ paper). If there is a XJ, the first one is likely to have been referred to as XK1 internally. There were three others of nominally 1790cc capacity called XK2, XK3 & XK4. It is likely these are what Haynes referred to as “XJ”. The first “true” XK was called “XK Number 1” (distinct from “XK1”) and was of 1970cc nominal capacity with a 83mm/91mm bore/stroke. Thus were developed the two block sizes that formed the basis of all subsequent XK 6-cylinder engines; the shorter block being used for the 2.4 and 2.8-litre engines and the full sized block for both versions of the 3.4, the 3.8 and the 4.2-litre engines. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Jaguar XK6 engine」の詳細全文を読む スポンサード リンク
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