The Jaguar XK inline six-cylinder engine had one of the longest production runs of any engine.
Visually, the most recognizable aspects of the XK engine are the dual cam covers atop the engine.
The cylinder head’s design was dictated by the desire to make room for two generously sized valves while not excessively restricting the flow of gases into and out of the hemispherical combustion chambers.
To do this, a relatively wide angle between the valves was initially chosen, with valve stems that are quite long.
Source: Underhood Service