Jaguar Classic, quite understandably, dedicates a lot of time to working on XK engines and E-Types. What other cars exemplify its heritage better?
It may not have been the first car to be powered by Jaguar’ s XK inline-six, but the E-Type is the most famous
is king. If without a package, you’ ve got no product,’ explains William.
The fundamental aspects of the XK straight-six are its cast iron block, two-valve-per-cylinder aluminium head and twin overhead chain-driven cams. Not forgetting its two polished cam covers, which give it its distinctive look. Held down with eight equally shiny cap nuts, the cam covers sit a significant distance apart from one another, allowing for a relatively wide valve angle – initially, 30 ° for the inlet and 45 ° for the exhaust – to allow for good flow, big valves and a hemispherical combustion chamber.
There’ s no one aspect that’ s exceptional about the XK straight-six, but its relatively simple specification was engineered with skill and care to make it not just beautiful, but a dependable and powerful engine. Its accolades don’ t just include powering some of the most iconic sports cars, but it was the foundation of Jaguar’ s reputation as the maker of the most exquisite performance cars, and it won many high-profile races, including Le Mans.
The very first XK, before the 3.4 launched in the XK120, was a 3.2 litre prototype engine. But by 1948, when it entered production, the stroke had been lengthened from 98mm to 106mm and, thanks to an 83mm bore, the capacity reached 3441cc. An 8:1 compression ratio and two SU carburettors helped it produce 160hp. To improve smoothness and refinement, a Metalastik vibration damper was added to the front pulley.
The first XKs grouped the front and rear cylinders into two pairs of three, with a bigger bore spacing between cylinder three and four for better cooling. The block only saw changes later, but almost from the start of the engine’ s life a variety of cylinder heads were available to help increase the XK’ s performance, all with much the same appearance and vernier cam sprockets for fine cam timing adjustment.‘ The really cool thing about them is they have different specifications, but all looking the same. They’ re just flowed differently,’ says William.‘ They were naturally well ported, they were beautifully machined, and fantastically reliable.’’
Autumn / Winter 2026 The Engine Rebuilder 21