cc version to the MG streamliner EX-135 in 1948 to take the 2,000 cc class record at , 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. Description Valve train The most recognisable feature of the XK engine is the dual cam covers atop the engine, which were a polished alloy until a change to ribbed black and alloy finish in early 1968, four years or so after the introduction of the 4.2-litre versions in 1964. The unusual depth of the engine's cylinder head was dictated by the desire to make room for two generously-sized valves, whilst not excessively restricting the flow of gases into and out of the hemispherical combustion chambers. To satisfy these two conditions, a relatively wide angle between the valves was initially chosen, with quite long valve stems. To efficiently operate valves whose tops were such a long way apart, the dual overhead cam arrangement was found to be the most effective. The cam lobes act directly on bucket type tappets, which are adjusted by means of shims between the underside of the bucket and the top of the valves. Two duplex chains drive the