Each piece appears simple, lying on a wooden table: a spring, a valve, a rod, a pin. But combined, these parts once roared to life and dominated endurance racing.
This story originally appeared in Volume 16 of Road & Track.
This is Jaguar’s XK engine. From 1951 through 1957, the inline-six mill cleaned house at Le Mans. A nearby poster from ’57 details that dominance. “The Fifth Jaguar Victory in Seven Years,” it proclaims, listing the 24-hour race’s finishing order: “1st Jaguar, 2nd Jaguar, 3rd Jaguar, 4th Jaguar, 6th Jaguar.”
The experts at Classic Jaguar in Austin, Texas, disassembled an example of our subject powerplant so we might better understand what made it tick. There may be no better guides on earth.
In 1994, Classic Jaguar’s CEO and president, Dan Mooney, left his career as a detective at Scotland Yard. He then left Britain altogether and by 1996 had set up shop in the States. He has dedicated his life to servicing, restoring, and improving vintage Jaguars of all stripes, especially those graced with XK engines. If any iron lump is worthy of worship, it’s the XK.
Consider its origins. As German bombs fell across England, a cadre of ingenious British engineers coalesced on Coventry rooftops. Led by (soon-to-be Sir) William Lyons, a small team from SS Cars—later renamed Jaguar Cars Limited—imagined the end of the war and, with it, an engine design that might last the company perhaps 20 years.
Instead, the XK spanned six consecutive decades in production guise, from its conception in the Forties, through the Fifties, Sixties, Seventies, and Eighties. Its swan song arrived in the Nineties in a series of royal limousines.
Mooney guided us through the disassembled six, from its coal-black iron block, stamped “Jaguar 3 1/2 LITRE,” on up through the pair of immaculately polished valve covers. While alloy blocks were occasionally used in some racing applications, this ferrous mass represents the Platonic XK engine.
Mooney noted that early XK prototypes were smaller, shorn of two cylinders. Those four-cylinder engines proved too coarse and underpowered, less refined than Lyons deemed appropriate. That decade of dominance at Le Mans proved Lyons’s foresight. Mooney noted production touches that lent the XK engine a solid foundation for racing, like the finely balanced crankshaft with its seven main bearings.
The aluminum head came next. It saves roughly 70 pounds over an iron equivalent, cutting precious weight while lowering the engine’s center of gravity. That crossflow head owes its clever design to Harry Weslake, a forward thinker and personal hero of Mooney’s. As exploration of the XK engine continued, we plucked the good bits from the table. Here are the highlights.
The only member of staff to flip a grain truck on its roof, Kyle Kinard is R&T's senior editor and resident malcontent. He lives near Seattle and enjoys the rain. His column, Kinardi Line, runs when it runs.
