Curbside Classic: 1973 Jaguar XJ12

Paul Niedermeyer
by Paul Niedermeyer

Jaguar and V12. Two of the most lyrical automotive icons ever. One stands for grace at speed, the other for speed with grace. The combination of the two offered the prospect of a marriage made in automotive heaven. Yet when they finally enmeshed, the result fell short of the potential envisioned by the marque’s match-maker and its loyal patrons. Yes, in those rare moments when the Jag V12’s stars were aligned , and its four carburetors synchronized, the results were heavenly. But in the final judgment, the V12 was a fall from grace, straight into automotive hell.

There’s a reason that skeleton head is sitting on the back parcel shelf of this XJ12. It’s the Prince of Darkness himself, whose presence hung over this graceful lump like a perpetual death wish, right from its genesis. Jaguar’s decision to build a V12 was a classic case of hubris, assisted by and its close relative, bad timing.

The origins go back to 1954, when it became obvious that the venerable long-stroke XK engine would no longer be competitive in racing. The first V12 designs were DOHC units, with a cylinder head arrangement similar to the XK. What Jaguar failed to take into account was that the classic wide-angle valve arrangement that worked so well on a long-stroke engine didn’t on a high-revving V12. The XJ 13 V12 racing prototype was obsolete from the get-go.

But Sir William Lyons was determined to have a production V12 for the new XJ sedan, due in 1968. That came with a huge price: the loss of Jaguar’s independence. The old XJ engine was built and assembled in the classic cottage-industry style: old-school castings and forgings, hand-fitted. The V12 would need an expensive modern transfer line and alloy-block casting facilities. The costs were more than Jaguar could raise itself, and thus forced the company into the arms of BMC, soon to be British Leyland. The “double-six” became Sir Lyon’s Jaguar death wish.

The V12 endured a protracted development (here’s the whole story in-depth), when it was decided that the DOHC hemi heads had to go. Instead, a SOHC (per bank) design with the combustion chamber in the cylinder/piston bowl (Heron head) was cribbed from a Coventry Climax engine. What Jaguar failed to do is ask Keith Duckworth why he had abandoned that design, due to its intrinsic limitations. Oh well. It took several more years to get it running right. It finally arrived in 1971, in the E-Type, and a year layer in the XJ, just in time for the energy crisis and tightening US smog regulations.

Its long gestation having begun before smog became a dirty word, the early V12 was crippled by the lack of fuel injection and a 7.8 to 1 compression ratio. In US spec, it made 241 horsepower, about the same as the best Chevy small block of the time. It did have that “turbine-like” smoothness, when the carbs were all synchronized, which was damn nearly never. That problem was swapped for others after 1975, when Lucas fuel injection appeared; its rubber lines had a bad habit of bursting, with resultant engine fires.

But the XJ6 sedan was a terrifically handsome car when it appeared in 1968, minus the V12, and would start a line of variants and successors that is just ending now. A particularly beautiful coupe graced us for a few of those years. The XJ became the definitive Jag sedan, having replaced a mish-mash of four overlapping obsolete models from which it inherited its IRS rear suspension and of course, the venerable XK engine. Only some 3k of the first series XJ came with the V12, which makes this CC a fairly rare bird, even if its wings are clipped.

Stateside, the V12 was mainly seen in the XJ-S, due to tightening CAFE requirements. Most XJ sedans soldiered along with the old XK engine through three series, until replaced in 1986 by the less-than satisfying XJ40 and its new but weak-chested 3.6 six. Just as well, as the old sixes are largely bulletproof, and parts will forever be available. The V12s will more likely end up like this one: nice curbside-side decoration.

It came and sat immobile, hunched over a speed hump in front of its owner’s rental house for the year they were there. Who knows what forms its ailments took; looks like mushrooms are growing on the driver’s side carpets (wet Wilton wool rugs, yumm). There were plenty of possibilities, starting from the internals out. The V12 block is an open deck aluminum affair, which means that if it overheats or blows a head gasket, the insides could end up looking like the engine photo I shot at a garage nearby (the mechanic/owner of that particular XJ-S said he wish he’d junked it, because he’ll never get his money back). You think? There’s a reason Chevy V8 swaps are so popular with the XJ-S.

Even if you can keep the internals intact, there is that insane four carb setup, a maze of

vacuum hoses, wires, relays and switches, and of course, the Lucas electrics and peripherals. No wonder the owner of this XJ spent all his time messing with his vintage motorbikes in the garage, and not the Jag.

But the XJ12’s quiet brooding presence added spice to an otherwise boring block around the corner from my house. It’s not like V12s are common sights on the streets of Eugene. Nor are Series 1 XJs. It will be missed. And its departure (on a flatbed) was notably lacking the element of either grace or speed.

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Paul Niedermeyer
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  • Compassion Compassion on Oct 02, 2009

    Caveat: I am a Jaguar owner of comparable series and have a bit more in-depth knowledge by performing my own service on these cars. I'd like to clarify some of the information regarding the the early Series XJ's. The Series I model years ran through 1968 till 1973. They rectified the cramp issues by releasing a long-wheel base version, that added 4 inches in the back, which was released in 1972. They also designed the XJ body to accept the V12 5.3L motor, with the aforementioned 4 carbs of hell, later in that 1972 year, although none of those V12 cars would be long wheel base, like the 1973 XJ12 depicted. The mention of the British-Leyland Rover V8-proof engine bay didn't come into play until the design of the XJ40, the replacement to the Series XJ's, that came out in 88. Ironically, this led to production of the XJ12 in this body until 1992. And by the time it mattered, Ford got in the mix by buying Jaguar. The AJ6/AJ16 4-valve motor wasn't a complete disappointment as mentioned above. It did achieve better performance than the XK predecessor, and wasn't as weak-chested as described. Not not as nearly remarkable, IMO. Jaguar was very aware of how terrible the situation was with the 4 carbs and later released the rebranded Bosch Fuel Injection, D-Jetronic, if memory serves, for the V12. There were some quality control issue with the hoses, but with all cars with this style of high-pressure fuel line fuel injection system, the replacement of the hoses every 5 years was a complete must. I do agree that the cooling system is of the utmost importance to be in working order on the all aluminum V12 motor. All it takes is one serious overheating and terrible things can be had to the motor. I have dealt with some of the rust issues, but they are nowhere near as exaggerated as above. There was a design deficiency in the cowl drains that could lead to condensation ending up leaking onto the front floorboards, and that was the typical cause of death for them. Keep that sorted and with some modern POR15 and life goes on nicely. Note: I am currently restoring a Series II Jaguar '79 XJ6L 4.2L, own a Series I XJ6 4.2L that is generally comparable to the depicted car above. I've also spent time inside and driving a '77 XJ12L. It is a delightfully smooth drive and a delight to work with, even if the Lucas electrics **** me off sometimes.

  • Sector 5 Sector 5 on Oct 22, 2010

    I wonder why the young mod old Honda and not tweek out something elegant like ol' jag? They'd have a cat that goes and not some beefed snuffbox...

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