Editing Jaguar XK engine (section)

==Early development==
Prior to [[World War II]], [[SS Cars Ltd|SS Cars]] (which changed its name to ''Jaguar'' in 1945) used three engines produced by the [[Standard Motor Company]]: a 1.5-litre 4-cylinder and 6-cylinder engines of 2.5 and 3.5 litres.  [[Sir William Lyons]] and his engine designers; [[William Heynes]] (Chief Engineer), [[Walter Hassan]],  [[Claude Baily]], and [[Weslake|Harry Weslake]]<ref>{{cite book|url=https://books.google.com/books?id=hedTAAAAMAAJ&q=%22harry+weslake%22|title=The Jaguar XK|author=Chris Harvey|date=1978|page=1|publisher=Oxford Illustrated Press |isbn=9780902280571}}</ref> are widely reported to have discussed a new range of replacements whilst fire-watching on the roof of the SS factory in Swallow Road, Coventry,<ref>"Sir William Lyons - The Official Biography" by Philip Porter & Paul Skilleter, Haynes Publishing, {{ISBN|978-0-85733-106-9}}</ref> during German World War II bombing raids. Rather than developing prototype engines immediately after the war, it is claimed that Jaguar's wartime engine developments went far beyond mere discussion and design, extending to the construction and testing of several prototype engines as early as 1943.<ref>Daniels, Jeff. ''Jaguar - The Engineering Story'', Haynes, {{ISBN|1-84425-030-X}}</ref>

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 [[brake mean effective pressure]] (BMEP), the new engines would need vee-opposed valves operating in [[hemispherical combustion chamber]]s. 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    1776 cc                                          May to Nov 1944
* XF  75 x 98 x 4   1732 cc                                                                     Nov 1944 to Jun 1945
* XK1 (first of Heynes’  4 x XJs)  76.25 x 98 x 4     1790 cc                       Oct 1945 to Nov 1946
* XK2  76.25 x 98 x 4          1790 cc                                                       Feb to Sep 1946
* XK3  76.25 x 98 x 4          1790 cc                                                       Dec 1946 to Feb 1947
* XK4  76.25 x 98 x 4          1790 cc                                                       Nov 1946 to Dec 1947
* Gardner Engine   (used in record-breaking MG car)   1970 cc                 1948        
* XK Number 1  3-bearing crank     1970 cc                                             1949-1952
* XK Number 2  3-bearing crank     1970 cc                                             1950-1952
* XK  5-bearing crank                    1970 cc                                             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 3,442 cc to form the "XK 6-cylinder", which saw its debut in an open two-seat [[Jaguar XK120|XK120]] [[sports car]] at the 1948 [[London Motor Show]].  Following this the XK powered the [[Jaguar Mark VII]] and a number of other 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,<ref>Heynes, W M. ''The Jaguar Engine'', a paper presented to the Institution of Mechanical Engineers on 27 February 1953</ref> 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 Mark 1|Jaguar 2.4-litre]] (retrospectively known as the Mark 1) released in that year. None of the 4-cylinder prototypes ever advanced to production but [[A. T. Goldie Gardner|Lt. Col. Goldie Gardner's]] speed record team did fit a 1970 cc version to the [[MG Cars|MG]] streamliner EX-135 in 1948 to take the 2,000 cc class record at {{convert|177|mi/h|km/h|abbr=on}},<ref>"British Racing Green - Drivers, Cars and Triumphs of British Motor Racing" by David Venables, Ian Allan Publishing, 2008, {{ISBN|978-0-7110-3332-0}}</ref> on the [[Jabbeke]] motorway in Belgium.

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 Heynes in a paper presented to the IMechE in 1953. Heynes 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 1790 cc capacity called XK2, XK3 & XK4. It is likely these are what Heynes referred to as "XJ". The first "true" XK was called "XK Number 1" (distinct from "XK1") and was of 1970 cc nominal capacity with an 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.