Magazine Subscription

Subscribe to Classic Motoring Magazine and save over 20%

Subscribe NOW

Available at all good newsagents including WHSmith

Do you drive this great classic or are thinking of buying one? Here’s how to ensure that you get the best out of your car for years to come

ENGINE OUTPUT

MOD

The MkX is E-type powered complete with triple but different carbs and inlet manifold so same tuning principles apply. 300bhp for road use is attainable with head mods and D-type camshafts – but it’s expensive. A milder budget alternative is to use a modded fuel injected XJ6 S3 head, cams and pistons. Ignition needs to be spot on so go electronc. Engine can be ‘mapped’ but it’s a dear upgrade. Daimler V8s and Jag’s own V12 slot in.

MEND

A properly maintained XK engine can see 100,000 with ease, the trick is to stretch its legs regularly and keep the cooling system in tip-top shape by keeping anti-freeze up to strength (or use Evans Waterless). Over silent tappets signify that they need adjusting and it’s best as a head off job; decoke and fit hardened valve seats at the same time. Later XK engines fit (and may have been substituted already) but watch the long stud type which aren’t as long lasting.

BOTTOM END

MOD

As with E-type, the 3.8 is the zestier engine, but, 4.2 lustier and suits this heavyweight better. Blocks can be taken out to 4.5-litre with even 4.7 achievable but it’s expensive. For better throttle response albeit at the expense of some smooth running (it’s always ideal to have this engine fully balanced during a rebuild), the flywheel can be reduced in weight to 19lb for road use.

MEND

Oil pressure should be 35-40lb @3000rpm when under load or a rebuild looms. Rear crank oil seal is a known leaker and a major job to rectify unless you are overhauling the unit; most owners live with it and keep lube just above the ‘min’ mark to minimalise loss. Lower timing chain renewal is a major head and sump off job but you may not need to completely remove the engine to do this.

FRONT SUSPENSION

MOD

Broadly Mk2/S-Type so usual tweaks apply. Needs stiffening to stop the sogginess, but it’s easy to compromise ride as a result; try a good adjustable damper such as Koni, Spax or Gaz. Most had power steering, variable rate on 4.2 and was good for its era but speak to a specialist regarding swap or modifying with electric conversion.

MEND

A heavy car, it understandably takes its toll on springs and dampers. Only wishbones are interchangeable with Mk2. Ball joint and track control arm wear common as are failed bushes (replace with good quality rubber or longer lasting, tauter, poly types) and power steering leaks. Keep an eye on the spring pans and mounts for rot.

BRAKES

MOD

The same uprating avenues apply to the MkX as they do the Mk2 or E-type, which you can use and there’s a host of excellent upgrades on offer (Zeus comes recommended) but you’ll need to ditch the original 14inch wheels for 15inchers. You can improve the brakes cheaper by fitting DS420 hardware boasting three-pot calipers and vented discs. Along with EBC pads, it will do the job admirably.

MEND

MkX used a unique brake system with special front callipers; rears are S-type. Kelsey Hayes bellow servo found on 3.8 is best replaced with later 4.2 or XJ6-types. Handbrake effectiveness always a bane although not as bad as many claim so long as system is set up correctly by a Jag expert.

TRANSMISSION

MOD

Three types were fitted; manual, overdrive but four out of five were auto. Overdrive is as good as a five- speed and there’s choice from the Mk2, XK6 etc, plus choice of higher rear axle ratios (up to 2,.8:1). If you want a five-speed opt for S3 XJ6 unit as it boasts uprated bearings. Automatic fans: the latter Jaguar four-speed auto unit can be fitted fairly easy.

MEND

S3 five-speed ‘boxes cheap (we’ve seen them for under £300) but budget on a rebuild. Automatics are tough but if in need of repair can cost over £700 (check state of unit by fluid colour and whether it smells ‘burnt’). Sluggish operation may simply be adjustment or old fluid. A GM400 gearbox from later DS420 fits and works well.

BODY & CHASSIS

MOD

We’ve seen low riding and customised MkXs as car lends itself to cruising. Jaguar made 24 limos based upon the 420G and such was the strength of the body that Jaguar expert, Craig Hinton, made a dozen stylish dropheads with a power hood. 420G platform, albeit lengthened, provided basis of the Daimler DS420 limo, used as hearses and wedding cars.

MEND

MkX rusts but not as badly as other Jags. Sills, valance panels, wings, pillars, doors and that huge bonnet rot; more serious are chassis members, especially front subframe mounts. Parts are available: front wing sections £100; rear ring part panels £220; sills £150. DS420 in service well into the 1990s giving scope for parts.

SERVICING TIPS

* ENGINE OIL: (20W/50 or 60): 13pints

* GEARBOX: (EP 90) 2.5 (four pints with overdrive unit)

* REAR AXLE: 2.75pints

* COOLING SYSTEM: 22pints

* SPARK PLUGS: Champion N5Y/N11 (or equivalent) 0.025in

* C.B. POINTS: 0.014-0.016in

* TIMING: 12 degrees BTDC Ideally set by vacuum gauge or strobe light

* VALVE CLEARANCES: (set by shims)

BODY AND TRIM

MOD

Some 40 bits of matched wood trim made up Rolls-like cabin, so restoration work will be equally as involved and expensive. The 420G featured a padded dash top along the lines of the 420 and also, unique to the model, perforated leather trim. Many cars boasted duo tone paint – if a mono shade is used, car should also have a chrome strip along the swage line. Air con and electric windows were features that can be retrofitted.

MEND

With those vast bumpers, it’s never going to be a cheap exercise to rechrome this Jag although a fair number of the smaller items were also fitted to the Mk2 and S-type so more attainable second-hand; 420G version has a unique hubcap design. Don’t rule out using exterior and interior items from a defunct Daimler DS. Vacuum-operated heater controls with twin heater fans were standard and differed from other Jags of that era.

REAR SUSPENSION & DIFF

MOD

It’s the same set up that is found on the E-type and S-type but neither are interchangeable. Has a tougher time due to the weight so replacing the cluster of void bushes with OE quality or poly alternatives are worth doing to restore handling and ride qualities; adjustable dampers are also good mod. Cars are quite low geared to counter weight, so some owners fit lankier ratios, like the one from the E-type S3 V12 (3.07:1) for better cruising and economy.

MEND

Apart from general bush wear, the biggest problem with the Jag’s famed IRS set up are weeping driveshafts and oil seals (specific to the MkX) which spew lube over the inboard rear brakes. Limited slip differential is rugged but must be serviced with the right type of axle oil or will fail prematurely. Rear end employs four dampers so are dear to overhaul and E-type and S-type springs don’t fit. Radius arm mountings known to deteriorate.

WHEELS & TYRES

MOD

While car employed E-type/Mk2 axles, 14inch wheels were fitted to the MkX/420G and for some time the right performance grade of 205 HR x14 (7.50 if crossply) section tyres were hard to obtain, although the situation has improved of late – try Longstone or Vintage tyres if you also want period rubberware. Many use XJ6 rims. We’ve never seen E-type wires fitted, but this doesn’t mean that this swap is not possible.

MEND

If you want to stick with 14 inch tyres, certain American wheels and rubber fit but the tyre choice may not suit the car. Many owners take the easy option of using S1 XJ6 rims on 205/70 x15 tyres as the hubcap can be utilised. It’s not original and some feel doesn’t look right, but apart from being a cheaper route, the lower profile tyres are available off the shelf plus will improve the car’s handling.

AND ANOTHER THING…

Two-thirds of the 24,175 made were left-hand drive. And while the 16ft 10in MkX was huge in its day, today a 2014 Mondeo is wider! If you want a MkX or later 420G (G stands for Grand) don’t be surprised to find the E-type engine has been pinched due to the saloon’s historical low values. As a more modern left field alternative, consider a DS420 Daimler limo which was produced from 1968-92 and was upgraded over the decades in tandem with the XJ6, (vented disc brakes for example). For help, go to M&C Wilkinson Mk10, who helped in this feature (01777 8180610) and check out Spares Market http://www.mk10.sm.wordpress.com.