The cars : Jaguar MkX/420G development story

The unhappy pinnacle

THE MkX/420G could be described as the forgotten Jaguar. It lacked the sporting image of the smaller Mk2 saloon and the glamour of the contemporary E-type sports car. Its bulbous styling did not make it one of the iconic cars to emerge from Browns Lane and it never received an image boost by being used in a cult film or television series.

When it was launched in 1961 the big MkX saloon was a cutting edge design. With a 120mph top speed, it was faster and better handling than the rival Rolls-Royce Silver Cloud III and considerably cheaper. And yet customers never really took to the MkX and sales were, in contrast to its now outdated predecessors, slower. The MkX was designed to replace the separate chassis MkVII, MkVIII and MkIX as the top of the range luxury Jaguar.

In 1958 when work began on the MkX, Jaguar Cars range consisted of the 3.4-litre XK engined Mk VIII, the 3.8-litre MkIX, the compact Mk1 saloon that ranged from 2.4 to 3.4-litres and the XK150 sports car. Codenamed Zenith, the MkX was intended at the outset to be a unitary construction chassis. The external style of Zenith was delayed by other events. Sir William Lyons was diverted by the restyling of the Mk1 compact saloon into the Mk2 and Jaguar’s purchase of Daimler in 1960. This did not prevent Jaguars Technical Director, William Heynes and his team of talented engineers from pressing ahead from developing the car’s internals. Heynes told his team to base the Zenith on a 120 inch wheelbase and the use of 14in wheels. However the track was as yet undetermined.

By abandoning the separate chassis and going over to unitary construction Jaguar hoped to save weight and make a lower profile car. The first unitary construction chassis Jaguar had been the 2.4-litre Mk1 saloon of 1955 which had its bodyshell manufactured by Pressed Steel Fisher Ltd. PSF would help in the engineering of the Zenith’s very stiff, some would say over engineered bodyshell and Jaguar would gradually become dependent on PSF for its bodyshells, which would lead to mergers that would threaten the future of the company.

Developing the style

Profile was resolved pretty much from the beginning.

William Lyons looks on, and seems quite happy with the results so far.

Front end treatment took some time to finalise.

…as this double-sided mock-up clearly shows.

The same model from the front three-quarters.

Note the semi-enclosed rear wheels…

Jeff Daniels in his excellent book Jaguar: The Engineering Story was not as impressed by the Zenith’s bodyshell engineering: ‘…it must be admitted that as an exercise in unitary construction, the MkX was not a whole hearted success. The main object of the unitary approach is to save weight by eliminating the separate chassis and distributing stress throughout the entire body, making each panel take its share. Yet the unitary construction MkX weighed 182lb or 4.5 per cent more than the chassis based Mark IX, taking a like for like comparison of 3.8-litre test cars weighed by The Autocar.

Was this because the MkX was bigger? Not really. Its 120in wheelbase was the same, its front track 1 1/2 inches wider, its rear track identical. True, the new body was nearly 6 inch longer than that of the Mark IX and it was 3in wider; but it was also 8 1/2 inches lower, and probably enclosed less actual space.

‘That it was beyond dispute heavier is almost certainly because of the conservative engineering approach, adopted for two possible reasons. First, it made sure the body would accept the stresses fed into it by an all new suspension system, and even more, perhaps, that it would be stiff enough not to suffer the apparent fragility, the squeaks and rattles, which plagued the 2.4 and 3.4, Jaguars first unitary construction models. The kind of customer who would buy the MkX simply would not put up with that kind of thing… One good reason for this conservative structural approach, not to make too fine a point of it, was Jaguar’s concern that the MkX would be stiff and quiet despite the worst that Pressed Steel quality control could do, and to judge by the 2.4/3.4 that was pretty bad.’

The MkX was earmarked the same engine as the E-type, a triple carburettor 3.8-litre XK unit. This developed 265bhp (SAE) at 5500rpm, and was to give a most impressive performance. The steering was Burman power assisted and there were disc brakes on all four wheels which were independently suspended. The independent rear suspension developed by Bob Knight was similar to that found on the E-type and would feature on most Jaguar models until 1996. Bob Knight would also be responsible for the smooth ride and lack of noise and vibration in the cabin.

There was a choice of Borg Warner DG automatic transmission or a four-speed manual Moss gearbox with overdrive, although the latter was an ageing and in many ways unsatisfactory design. Originally Jaguar had intended only to offer Zenith with automatic transmission, the decision to offer the manual option was taken towards the end of development. The Zenith began the tradition of having twin petrol tanks with a fuel capacity of 20 gallons.

Eventually the external style was decided on by Sir William Lyons. The radiator grille sloped at the ‘reverse angle’, which. gave it a look of purpose and urgency. There were twin pairs of headlamps, the MkX was the first Jaguar to use this styling cue and the quad light look lasted into the next millennium. The car was a full five-seater and there was plenty of leg room at the back. Although it was more spacious than its predecessor the profile was considerably lower and this gave an impression of far less bulk. Certainly the MkX looked sleeker than the outgoing Mk IX, but its appearance still came as something of a shock to journalists when it was announced on 12 October 1961.

At the time it was the widest British car on sale. In fact at the time Jaguar were in no position to commence deliveries to customers as due to delays at Pressed Steel Fisher there were no cars ready. Production proper did not begin until December and deliveries did not commence until the winter of 1961/62.

On to launch… the road testers approved

In October 1961 Jaguar recieved a £22,500,000 order placed by its North American distributors. Jaguar had exactly 12 months to build and deliver over 10,000 cars and they had to strictly comply with the delivery dates specified. 40% Of this order was for MkX saloons. The trades unions pledged their support, but thirteen days after the order was placed there was trouble. About 150 men walked out in a dispute involving the companies new MkX car, and as a result 500 other workers had to be sent home. The strikers, all employed in the trim shop, complained of excessive waiting time -the lapse between jobs, when the men got a lower rate of pay.

A company spokesman said: ‘This is a wildcat action. a complete breach of contract. There is a shortage of work in the section caused by the changeover in production from Mark 2 to Mark 10. There can be no negotiations until the men return.’

The stoppage halted Mark 2 production. The strikers were members of the National Union of Vehicle Builders, whose district organizer, Mr Charles Gallagher, said: ‘This is more than a slightly wildcat action. Even when the men go back there will be no negotiations because there is simply nothing to negotiate.’

The 500 workers who had to be laid off returned to work the next day. In early February 1962 there was another unofficial strike by 4500 men which cost Jaguar around 700 cars in lost production. It took Jaguar several days to get back to normal operations. In March 1962 the MkX was released onto the home market. In May it was the turn of 400 trim shop workers to halt production.

On 1 October 1962 there was yet more trouble. Around 6000 men went on strike at Browns Lane and production was stopped completely. Trouble began after the firm’s decision to dismiss a man employed in the oil cleaning shop after an alleged assault on a foreman. The joint shop stewards committee recommended the strike because no action was taken against the foreman. While the stewards were meeting, trouble broke out on the MkX assembly line, where men objected to the transfer of 20 workers from the Mk2 line to increase track speeds. A company official said the firm was insistent that quality production could be maintained only if these men were transferred to the line. A return to work was later agreed.

A company official said later: ‘A partial return to work will take place tomorrow, but no car production will be possible, owing to a shortage of chrome- plated parts, following the unofficial strike in the plating department on Wednesday and the employment of go-slow tactics on Thursday and Friday of last week.’

This was the atmosphere in which Jaguar struggled to produce its cars. To many pundits the MkX had been aimed at the important American market with its wide cabin and park bench seats, although by American standards it was a small car. Inside there was lavish helping of polished walnut and Connolly leather. The reception of the new Jaguar was mixed. While there was praise for the cars engineering, the press was less complimentary about its looks.

Autocar magazine did not manage to get its hands on a MkX until November 1962 when they tested 8172 RW, an automatic. Top speed was 119.5mph, the 0-60mph time was 10.8 seconds and fuel consumption was 14.1mpg.

8172 RW had 13000 miles on the clock and Autocar paid it several compliments: ‘There was not a body creak or rattle… almost sports car stability through fast bends and over rough surfaces……..The aroma of good leather pervades the interior, and this with an abundance of timber veneer gives it almost the cosily affluent air of Edwardian library’.

A year passed before the rival Motor magazine tested a manual overdrive MkX, 1196KV. With 1196KV, the men from Motor attained a top speed of 120mph and a 0-60mph time of 10.8 seconds. Overall fuel economy was 13.6mpg. However the magazine was not so complimentary about the car as their rivals.

‘If the car cost another £1000 (it then cost £2082), as it reasonably might, no doubt the sound damping and trim would be much better. Although generally quiet, the engine and gearbox can be clearly heard under heavy acceleration and the decorative woodwork has a skin deep quality, revealed by close inspection. Like the gracefully bulbous sides that make for thick doors rather than interior space, effect has been placed before function: some people like it, others do not. An absurd lack of lateral support mars the otherwise comfortable seats in which five people may stretch and relax, and there is vast luggage space in the boot. Heating and ventilation fall short of many cars costing a third as much. The excellence of the handling, brakes and steering all masked under certain conditions by various shortcomings, and the manual gearbox, although mastery of it can give great satisfaction, is elderly in design and, to most drivers, out of place in such plush surroundings. The automatic alternative is a more natural choice.’

This apparent critique of a Jaguar incurred the wrath of the Coventry concern and the editor of Motor ended up writing an apology to the company.

Developing the beast

Meanwhile in this pre-energy crisis world, fuel was still relatively cheap and a horse power race broke out in the USA as manufacturers built more and more powerful engines with larger capacities. Jaguar was in danger of being left behind. The company had two choices: develop what it had or build an entirely new engine. When Jaguar had bought Daimler in 1960 it had inherited a failing car range, but two excellent overhead valve V8s of 1959 vintage designed by Edward Turner. The first was a 2.5-litre unit producing 140bhp and 146lb ft torque, more than the equivalent 2.4-litre XK engine. Further more, when slotted into the Mk2 bodyshell to produce the Daimler 2.5-litre V8, it produced a faster car than the smaller engined Mk2 2.4, and in the opinion of most critics, a more refined car.

The second was a 4561cc V8 which produced 220bhp at 5500rpm and an impressive torque figure of 283lb ft at 3200rpm. This V8 was fitted to the Daimler Majestic Major which was in production from 1959 to 1968. Sales of the latter were low but it could match the Jaguar MkX for top speed and beat it on acceleration quite handsomely. The logical next step was to try and fit the 4.5-litre V8 into the Zenith bodyshell to create a Daimler version of the MkX, which was duly done. Physically the V8 fitted into the engine bay quite easily, and ex-development engineer Ron Beaty recalled how it performed.

‘It lopped six seconds off the 0-100mph time, and that was with square cut exhaust manifolds and an air cleaner you wouldn’t put on a lawnmower. It buzzed around MIRA all day at 133/134mph in the hands of anyone who happened to be about’.

Around this time Jaguar Technical Director William Heynes wrote to chairman Sir William Lyons on the subject of the larger Daimler V8: ‘There is no question that the horsepower can be brought up by redesign of the valve ports. At the same time I feel it is desirable to increase the capacity of the engine. I have therefore arranged with Daimler to revise the design to bring the capacity up to five-litres which, with revised valve ports, should produce 280/290bhp at 5000rpm with a 30% increase in maximum torque over the Jaguar 3.8 engine. The unit in this condition would give a satisfactory alternative unit for the Zenith (MkX) and also a satisfying performance in the big Daimler saloon’.

In the event the company decided not to proceed with a Daimler V8 version of the Zenith saloon. The official reason was that the the Daimler production line was not tooled up for quantity production, but it had no trouble supplying demand for the smaller 2.5-litre V8. Perhaps the real reason was one of prestige. A 5-litre Daimler Zenith would have embarrased the XK engined Jaguars in the performance stakes, Jaguar’s engine designers also had a blind prejudice against the V8 configuration, which they thought could not match six and twelve cylinder for refinement and they thought they could design a superior V12 engine. In the event it took until 1996 for Jaguar to produce a V8 engine, the superb AJ26, which in 2009 was enlarged to 5-litres.

In the meantime Jaguar decided to enlarge the XK engine from 3781 cc to 4235cc. On 6 October 1964, Jaguar announced the new 4.2-litre XK engine for use in the MkX saloon and E-type. The new engine boosted torque from the 3.8-litre’s 260lb ft at 4000rpm to 283lb ft at 4000rpm. The quoted power output remained at 265bhp (SAE), but now at the slightly lower 5400 rpm. Along with the new engine, came a new all-synchromesh four-speed gearbox designed by William GJ Watson, which when fitted to the MkX came with optional overdrive. Automatic transmission was now the Borg Warner Model 8.

Also among the revisions was a new power steering system which was called the Marles Varamatic Bendix which was further developed and manufactured by Adwest of Reading. The revised MkX was given the factory code XJ5 and was being produced at a rate of 75 per week.

Autocar magazine tested a revised 4.2-litre MkX automatic in October 1964. They managed a top speed of 121.5mph, fuel consumption of 14.5mpg and a 0-60mph time of 9.9 seconds which fulfilled Jaguar’s ambition to create a faster car than the Daimler Majestic Major.

The magazine commented: ‘On the road the improvements are really appreciated, and the car covers the ground in the forceful, tireless manner of the smaller Mk2 models… Ride comfort is at its most impressive when the car is at speed on a good road, and the luxury of the Mark 10’s 100mph cruising on a motorway approaches the refinement and isolation from ones surroundings that goes with modern air travel. Wind noise, with the windows closed, does not drown conversation in normal tones; and both road and mechanical noise are also at a minimum… Spaciousness, comfort and a very high performance remain the chief selling points of the Jaguar MkX, and in the new 4.2-litre these are now allied to more precise control to go with the extra power. The price (£2156) is in the usual Jaguar tradition of exceptional value for money.’

It was not until a year later that the magazine got their hands on a manual overdrive 4.2 MkX. This time the top speed was 122.5mph, petrol consumption was 16mpg and the 0-60mph dash was completed in 10.4 seconds. Autocar commented on the new manual gearbox: ‘The latest all synchromesh gearbox is a great improvement over the superseded unit, and has an excellent set of indirect ratios, such that one is rarely short of a suitable gear for any traffic situation. Movement between gears is quite long, but the gate is well defined, and the synchromesh quite unbeatable. Second gear, with a useful maximum of 54mph, and third, good for 81mph, are both exceptionally useful for sweeping past slower vehicles.

Such is the combination of well bred power, nicely matched ratios, and an easy gearchange that even the most timid driver would find himself pushing the Mk X along very quickly on almost any sort of road, yet at city traffic speeds it is restrained and quiet.’

Autocar also compared the £2261 MkX with rival cars. The only car that was cheaper was the Vanden Plas Princess R which could manage 106mph. The £3630 Buick Riviera was 1mph slowers, and also trailing in the Jaguar’s wake was the £4086 Mercedes Benz 300SE and the £5632 Rolls Royce Silver Cloud. Around this time Jaguar announced that the MkX would now be fitted with an optional full air conditioning system. Also in 1965 Jaguar introduced a limousine version of the MkX complete with central sound-proof division. 18 cars were built.

On 11 July 1966, Sir William Lyons sold Jaguar to BMC, although he retained control, to form British Motor Holdings. By doing this Lyons secured the future of his body supply from PSF which was now owned by BMC and funding for a next generation of models.

MkX becomes the 420G

On 13 October, Jaguar announced another revision to the Zenith project when the MkX was renamed as the 420G. Rather confusingly at the same time the company announced the 420, a facelifted S-Type with the quad headlight look. The 420G recieved a new grille, chrome beading along the flanks, a padded dash rail and revised wheel trims. A limousine version continued to be available and another 24 examples were manufactured. Although not actually specified, the ‘G’ is believed to have stood for Grand. Mechanically the car was unchanged.

While all this was going on Jaguar were working on the car that would replace the MkX/420G and all the other Jaguar saloons, the project codenamed XJ4 and eventually released to the public as the XJ6 and later still as the XJ12. The MkX/420G would become the testbed for various XJ components including the V12 engine. The V12 MkX/420Gs were codenamed XJ10 and were used to help Jaguar decide on whether to opt for a quad cam or twin cam V12 engine. The four cam XJ10 gave smooth but unspectacular acceleration up to 3500 rpm but beyond that point it really took off and had a maximum speed of nearly 150mph, but in the end Jaguar opted for the ultimately slower twin cam V12 as it offered more low down acceleration where it mattered in real world driving.

In 1968 the Zenith/XJ5 platform spawned the XDM3 Daimler DS420 Limousine using a stretched floorpan and 4.2-litre XK engine. This long lived vehicle survived until 1992 and was the last to use the XK engine, ceasing production after 5043 examples. Also in 1968 the ill fated British Leyland Motor Corporation was formed with Sir William Lyons as deputy chairman and Jaguar at the pinnacle of the car range. With Rover and Triumph in the fold with their 2000 saloons, which were in the process of receiving larger engines, Jaguar did not need to replace the now ageing Mk2 based compact saloons and could concentrate on the one model XJ4 project.

In September that year, Jaguar announced the XJ4 project as the XJ6 saloon. In terms of ride, handling, refinement, stability and comfort it was a quantum leap. Journalists fell over themselves to award superlatives to this car and a huge waiting list soon built up of customers wanting to buy this new automotive sensation. The XJ6 made all Jaguar’s existing cars obsolete and the company got down to the task of rationalising its range. By axing its existing models, the company freed-up Browns Lane to satisfy demand for the new car. First to go was the Jaguar 420 in August 1968; that was quickly followed by the Mk2 240 in April 1969; the Daimler Sovereign in July 1969; and the V8 250 in August 1969.

Only the Mk X/420G survived the cull – for the time being. It remained the companies range topper. When the XJ6 was launched, the top of the range 4.2-litre interestingly used the twin carburettor XK engine rated at 220bhp SAE, in reality a more honest 173 bhp DIN, while the 420G continued to use the more powerful triple carburettor unit, perhaps as a sales incentive.

By October 1969, the 420G range topper was listed at £2671, compared to £2475 for the XJ6 4.2. A difference of £196, which equates to £2500 in 2009 terms. It was sold as a luxury car powered by the more powerful 265bhp XK engine, but demand wasn’t strong and Browns Lane probably built no more than around 30 cars per week. The demand for the XJ6 was such, that the big car was phased out in June 1970, leaving the XJ as the sole saloon representative in the range. The 420G’s place on the assembly line was taken by yet more XJ saloons. And the void created by the demise of Zenith/XJ5 was filled by long wheelbase XJ Jaguar and Daimler variants, being joined by the XJ12 in July 1972.

Only 25,211 Zenith/XJ5s were produced in nine years, Jaguar would later produce more XJ saloons in a year. At its peak the Mark 10 was produced at a rate of 110 a week, but by the time the 420G came along only 30 were being produced weekly. Of course the other thing that needs to be asked with such a low production figure, did the big Jaguar pay its way?

Jaguar 420G was the UK’s widest car when it was launched.

Zenith/XJ5 production
MkX 3.8-litre 12,977
MkX 4.2-litre 5680
420G 6554
Total 25,211

Written with reference to: Jaguar, the engineering story – Jeff Daniels

Ian Nicholls
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  1. A nice write up – I never knew of this forgotten sibling of the Mk2/S-type and XJ.

    Anyway, for all the “bulbous” styling of the time, it still looks elegant.

  2. My dad had one. I was very proud! However, the ride was so floaty that my best friend was always sick whenever he went in it.

    • One of my school friends, his father owned one from new and the poor lad was travel sick time on many journeys, so the Jaguar was sold and replaced by a Rover 2000

  3. Ha ha! I was sitting in the pub with a girl I’d been out with a few times, when I saw out of the window one of these rare old beasts pull into the BP station opposite. Being a Jag lover to the core I broke off our conversation to say, “A Jaguar MK X! Look behind you, look! The widest car Jaguar ever made, and that was designed by the same bloke who did the London cab.”
    She looked me directly in the eye and said “I am actually impressed you know that.”
    And seeming as I’m still in correspondence with her, I can’t have been that bigger mistake can it?!
    😀 I’ve had a soft spot for them ever since!

  4. I owned one of these cars for 16 years, a 1970 420g, toured europe (7 countries) several times. A superb vehicle, very under rated, usually criticised by people who, when carefully questioned, admit theirs cost £50, had 130,000 miles on the clock and had been used by it’s previous owner to tow a stock car to race meetings!!

    Anyone who bought a new one or a well maintained second hand example, will tell you a very different story. Check the oil regularly, because the XK engine was designed to use a little oil, and these engines were ‘bomb proof’, the automatic gearbox prevented any over revving even when driven enthusiastically, the ‘finger tip’ power steering was superb once you had got used to just how light it was. I wish I still had it, no car has ever pleased me as much since!!
    Two and a quarter tonnes (with both tanks full) and an auto box, yet the 420g would still effortlessly ‘slaughter’ most cars away from the lights, Mercs, Zephyrs, Crestas, Stags, Capris, BMW’s you name it, they couldn’t live with the big Jag.
    In the days before we had to wear seat belts to hold us in place, being such a wide car with ‘slippery’ leather seats, it did have a tendency to toss your passengers around, or should I say, I tossed my passengers around, there were plenty of ‘chunks’ of polished timber in there too but I don’t remember ever knocking anyone out!!!
    Happy Days!!

  5. I quite agree with Will Lyons post. I had a 3.8 MK 10 with the manual plus overdrive transmission in the opalescent blue as found in the last picture in the article. I found it to be a wonderful car to drive, especially on the highway where it felt like it prefered to travel at speeds in excess of the 70 mph speed limit. As the article indicates the Moss gearbox took some getting used to but felt strangely appropriate to the car.

    I later had a 420G with the automatic transmission and found this to be a much heavier car — more luxurious but no where near as much fun to drive as the Mk 10 with the 3.8 motor.

    I miss both cars but it is the 3.8 that I miss the most.

    The width of the car was partly due to the fashion of the times. It should be noted that 1961-1962 is the time when American cars were reaching their maxmimum width and prompted the establishment of a maximum width for all cars.

  6. I’ve just completed a TOTAL restoration of my fathers 1970 420G (He bought it new) Plenty of history. It took me 9 months with a lot of help from a garage friend to complete. The most expensive part was a new water pump imported from Australia.(£600.00) I did it for my two daughters weddings this year. It is Automatic, and Willow Green over British Racing Green. I will enjoy the summer rain free days riding around the Yorkshire countryside like my Father did 42 years ago.

  7. It has dawned on me since I originally wrote this article that the relative failure of the Mk10/420G was a major setback for Jaguar in their expansion plans. The XJ6 of 1968 was in fact their second bite of the cherry.
    The Mk10 of 1961 was Jaguar’s most advanced car to date and had it sold up to 30,000 units a year like the later XJ saloon did, then the financial outlook for the company would have been transformed.
    Instead Jaguar production stagnated during the 1960’s as the company introduced the stopgap S-Type and 420, while trying to develop the XJ6. The company was forced into mergers with BMC and Leyland in order to find the resources to bring the XJ6 to fruition. There was no money for a replacement for the Mk2 saloons or a direct E-type replacement to slot below XJ-S.
    When the XJ6 did appear it ran into the energy crisis and the window of opportunity closed.

  8. Fantastic reading and new insights in to the history of the MKX/420G.
    I have just acquired my own example – trying to find out more of the history, but apparently an embassy car and then owned by a publishing company that I worked for – I saw it parked i the basement parking garage where it was cared for by the chauffeur/mechanic. I only has 30 odd thousand miles on the clock which couldvery well be original milage given its fantastic condition.
    It has an unmarked interior, engine bay with patina, paint that aslo shows that it has been cared for, but not perfect – maybe 97% perfect 🙂
    After the publishing company ownership it has had two lawyer owners who have both taken really good care of her. I’ll look forward to putting som classic seatbelts in and taking my familt for sumer drives and holidays.

  9. I think that the relative “flop” is due to the fact that it looked like a big -at best, I’d say seriously bloated- MKII/S-Type, lots of car makers have made the same mistake again and again, but the germans ie: new S-Klasse in 1980 spawned the 190 and e-Klasse, same as Audi’s aero 100 lead to the new 80/90 and coupes. The new design identity came from the top and then filtered down the entire model range. Look at Peugeot, superbe 405 yet the 605 didn’t work (other way round might have helped…) Renault made the same mistake, the 25 was a big Fuego saloon. It’s better to be a scaled down version of the “HALO” model than an upscale of the lesser ones…
    Still, how could they ignore the V8 Daimler for US export? Another might have been to ad to the portfolio, though this one is NOT BL/BMC/BMH fault, Sir William you didn’t do your home work properly and put pride before survival. This car deserved a V8 of 5L… Funny, 20 years later, the Buick-Rover V8 didn’t fit XJ40 either!!! That would be in line with the corporation’s MOTTO in the decades to follow, unfortunately…

  10. I have had Jaguar Mk10 and Jaguar 420G for a long while now. They are fantastic cars, but I found that the fuel tanks accumulate water which makes the tanks rust. I have had the Mk10 tanks done, but I can’t get the fuel pumps as I want to replace them too. Where do I get fuel pumps from? Can someone tell me?

  11. In 1968 I was the office junior and my boss would sometimes arrive at our Mayfair office, throw me the keys to his 420G (PLU 707E), ask me to fill it up at the petrol station where we had an account and then take it to the car park. The guys at the filling station stuck one nozzle in each of the fillers and we waited for what seemed like hours while gallons of 5 star gurgled into the twin tanks. The 17 year old then went for a cruise around the local West End neighbourhood, wafting along totally insulated from any outside sensations. A wonderful, if all too short experience for someone whose only motoring experience thus far was driving (and writing off) a Renault Dauphine.

  12. Bello David,

    Would it be posible to share some information about the water and duul tanks als i have à full restored 420g 4.2 Ltr rhd from 1969. Imported in 1996 to the Netherlands.

    I would go to sng barrat they have fuel pumps on stock to sell for 75 euro shipped and home delivered within 24 hours 🙂

    Kind regards,


  13. Lovely article, thank you very much for putting it together.

    One tiny niggle.
    Autocar magazine tested a revised 4.2-litre MkX automatic in October 1964. They managed a top speed of 121.5mph, fuel consumption of 14.5mpg and a 0-60mph time of 9.9 seconds which fulfilled Jaguar’s ambition to create a faster car than the Daimler Majestic Major.

    Majestic Major 0-60 9.6 Motor Sport June 63 I think.

  14. i have just acquired a 420 g in toronto fully restored green with red leather interior
    ride is exceptionally smooth and quiet.i drove over 300 km at a stretch on 401 cruising at 120 km engine was very responsive,in short a very comfortable is a great car .at shows it is crowd puller more than my 57 silver cloud ,may be because it the only one at the show

  15. We have the pleasure of being in the position to offer a superb 1969 420G with under 20,000 warranted miles from new and a known and interesting history – and we totally in agreement these cars are truly remarkable.

  16. Hi, ice loved reading all these posts. But, can anyone tell me if there was a Daimler equivalent of the 420G like the Sovereign version of the 420? Sorry if this is an obvious one.

    Thanks b

  17. Fascinated by the Mark X/420G’s more accurate 173 hp (DIN) rating for the (220 hp SAE) 4.2-litre engine, it would be worthwhile seeing an article on the XK6 engines that finally demystifies the SAE rated versions by converting them to DIN.

  18. I’m not quite sure where you get 173 DIN for the 4.2 litre Mark 10/420G, as the DIN ratings really hadn’t been formulated at the time of those cars . It is not possible to extrapolate late 1970s or 1980s figures backwards from the similar but not identical XJ6 engines, because the XK engine was badly affected in terms of power by all the emissions changes that were necessary from the early 1970s onwards. The only public DIN figure that I can recall for the 4.2 was 205HP DIN for the S3 XJ6 4.2. This was fuel injected, but optimised for emissions, and without that would probably have produced in DIN terms something like 225 HP or possibly slightly more

  19. German registration documents (and brochures) always had DIN figures. Whilst these differed vastly from american SAE hp values, the difference to the UK values was not so big. For the Austin 1800 S from 1969 it was 97 PS (DIN) for the German documentation…
    If I remember rightly, the E-type 4.2 was sold in the US with 265hp (SAE), while German documents show 210PS (DIN).

    • Interesting, so the German registration documents and brochures could be used to provide more accurate DIN figures for the XK6 engine.

      • Nate : rather too much water has now gone under the bridge for me to be accurate , but there were wide variations in power depending on the emission situation in any given market. Your 173 for an XJ6 might well be for the de-smogged Californian version . The S3 in the UK market was definitely 205DIN on FI, and IIRC the 3.4 was 161DIN on de-smogged twin SU HIF6 . It is interesting to reflect that the last non-emission MGB was 91DIN from 1798cc. I cannot think that the specific power of any XK would be less than an equivalent MGB and for 4235cc the same specific power would produce 4235/1798 X 91 = 215 DIN which sounds to me to be close enough to Alexander’s figure and indeed to the bracket of 215 – 225 which I posted earlier

        • Do not disagree, was thinking an XK6 article could draw upon the Rover V8 article with regards the varying outputs resulting from the emission regulations in different markets. Not entirely perfect though at least a starting point.

  20. A slight correction to the article, the Jag Mk10 was used in a film – the Krays. Maybe this article was written prior to that film coming out? The actual car after the film was made was poorly stored and sold on Ebay in poor condition and didn’t fetch a lot.

  21. I have a very rare 1965 Mark 10 convertible with the 4.2 litre engine it was done in the mid 1980’s by Graig Hinton of Hinckley it’s now fully restored, it looks fantastic and drives like a dream and better than my 1965 Bentley S3 convertible. The Mark 10 Jaguar is the epitome of Jaguars adage ‘Grace, Space and Pace’. As a convertible, it looks better than the saloon!

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