Guide: Jaguar XK120
Background
Having been a partner in the Swallow Sidecar Company since its 1922 inception, Williams Lyons purchased the business in 1934 and renamed it SS Cars.
The first Jaguar-branded SS subsequently appeared in September 1935 (the SS Jaguar 2.5-litre sports saloon). This was followed soon afterwards by the renowned SS Jaguar 100 3.5-litre open two seat sports model.
At a meeting of the SS Cars shareholders on March 23rd 1945, it was agreed to change the company’s name to Jaguar Cars.
Production of Jaguar’s existing saloon models continued after World War 2. However, the firm’s rise to an industrial power house began with two new cars that were publicly introduced at the London Motor Show in October 1948.
The Mark V was available as a luxurious executive saloon or a Drop Head Coupe. Overhead valve pushrod straight six engines of both 2.5 and 3.5-litres were offered. Styling followed the lines of the pre-war SS Jaguars with an upright grille and flowing old-fashioned fenders.
Displayed alongside was a rakish two-seat sports car widely considered to have been the star of the show: the Jaguar XK120.
Thanks to its stunning modern lines and state-of-the-art specification, the XK120 caused a sensation. It was presented in Open Two Seat (OTS) Roadster configuration. The ‘120’ moniker was reference to an anticipated top speed of 120mph which would make it the fastest production car available.
Jaguar initially conceived the XK120 as a show car with which to premier their advanced new 3.4-litre dual overhead camshaft straight six engine designed by Chief Engineer, William Heynes. However, the public response convinced Chairman William Lyons to put it into production.
An intensive development programme was undertaken and, come June 1949, the first production cars began to roll out of Jaguar’s Holbrook Lane factory in Coventry.
Chassis
The XK120 was built on a shortened, simplified and lightened version of the MkV’s box-type chassis. At 102-inches (2591mm), the XK120’s wheelbase represented an 18-inch or 457mm reduction over the MkV.
Independent front suspension was via wishbones, torsion bars, Newton telescopic dampers and an anti-roll bar. The live Salisbury rear axle was located with semi-elliptic leaf springs and Girling lever arm dampers.
12-inch Lockheed drum brakes were fitted all round along with 16 x 5-inch solid steel wheels. The wheels were originally fitted with chromed hub caps and Dunlop RS5 tyres.
A 14 gallon or 63.6-litre fuel tank was installed over the rear axle.
Engine / Gearbox
The William Heynes-designed straight six engine was arguably the most advanced mass produced power unit around.
It comprised a cast-iron block and aluminium alloy head with dual overhead camshafts, hemispherical combustion chambers and inclined valves. Wet-sump lubrication was employed along with single plug ignition and a Lucas B12 coil.
Displacement was 3441cc thanks to a bore and stroke of 83mm and 106mm respectively.
Two SU H6 sidedraught carburettors were fitted and, for most markets, a compression ratio of 8.0:1 was adopted. In this configuration, peak output was 160bhp at 5000rpm and 195lb-ft at 2500rpm.
For some markets (including the UK, where post war austerity measures meant only 70 octane fuel was available), the compression ratio was dropped to 7.0:1.
Jaguar also planned to offer a two-litre four cylinder version designated the X100, but this idea was abandoned early on.
Transmission was via a Moss four-speed manual gearbox.
Bodywork
As exciting as the mechanical specification might have been, it was undoubtedly the XK120’s stylish bodywork that ensured it stole the headlines.
All four wings were fully enveloped and flowed gracefully backwards to give an extremely streamlined appearance.
At the front, Lucas headlights were mounted inboard of the wings. A vertically-mounted oval grille was located between the lights and a pair of wraparound chrome bumperettes.
The cockpit was set well back and featured a split windscreen that could easily be removed for racing.
Cut down doors merged into a tapered tail with vertical overrider-style bumpers. Rear wheel spats further accentuated the XK120’s aerodynamic profile.
The first 242 cars came with wood-framed OTS roadster bodies built entirely from aluminium.
Once removed, the simple canvas hood with its detachable side screens could be stowed behind the seats.
As there were no exterior door handles, entry to the cockpit was by an interior pull-cord. When the weather gear was in place, the door pull cords were accessed through a flap in the sidescreens.
Interior
Interior equipment included a four-spoke Bluemels steering wheel mounted on a telescopically adjustable column.
Located in the centre of the dash was a rectangular binnacle which housed a large rev counter and speedometer plus smaller read outs for fuel, battery condition and a combined oil pressure / water temperature gauge.
Leather was used to upholster the dash, door caps, door panels, the seats, armrest and the handbrake and gear gaiters.
Options
Options included aero screens, a close-ratio gearbox, fog lights, bucket seats, Dunlop racing tyres, a choice of Radiomobile radios, a long-range fuel tank, an underbody steel protective shield, a chromed luggage rack for the boot lid and a white Bluemels steering wheel.
Two-tone upholstery could be specified for the dash, seat centres and armrest.
Some cars were also fitted with finned aluminium Alfin brakes to help overcome fade.
Weight / Performance
The alloy-bodied OTS XK120 weighed in at circa 1200kg.
With a 125mph top speed, it could rightfully claim to be the fastest production car in the world.
0-62mph required just over nine seconds.
Prototypes
The right-hand drive prototype displayed at the London Motor Show in October 1948 was chassis number 660001. This car looked almost identical to production versions except for its straight outer windscreen pillars which subsequently became curved.
Left-hand drive chassis numbers began at 670001.
1949 Jabbeke Speed Run
In addition to appearances at motor shows and road tests in noted publications, Jaguar decided to promote the XK120 through speed records, races and rallies.
The first of these high profile outings was on May 30th 1949 when Jaguar took a white left-hand drive prototype (chassis 670002) to a closed section of the Ostend-Jabbeke motorway in Belgium.
The car was fitted with a full-length aluminium undertray and the tallest possible gear ratio. It was piloted by Jaguar test driver, Ron Sutton, who was filling in for the unwell Walter Hassan. Timing was carried out by officials from the Royal Automobile Club of Belgium.
With the windscreen, hood and side screens in place, Sutton achieved a two-way average of 126.5mph.
The hood and sidescreens were then removed, the windscreen was replaced with an aero screen and a rigid tonneau was fitted over the passenger side of the cockpit. In this configuration, Sutton averaged 132.6mph.
1949 Silverstone International Trophy 1 Hour Production Car Race
When the British Racing Drivers’ Club announced a one-hour Production Car Race in support of the first Silverstone International Trophy for Grand Prix cars on August 20th, Williams Lyons felt compelled to have a trio of patriotically coloured XK120s attend.
In anticipation of the Silverstone outing, the three XK120s underwent special preparation.
Chassis 660001 (the original right-hand drive prototype and 1948 London Motor Show car) was repainted blue (from its original bronze) and entered for Prince Bira. Chassis 670001, the first left-hand drive prototype, was repainted red (from its original bronze) and entered for Peter Walker. The white Jabbeke record car, chassis 670002, was entered for Leslie Johnson.
670001 and 670002 were both converted to right-hand drive for the race. The conversion was a straightforward process carried out to stop the right-hand rear wheel lifting on right-hand turns.
Chief opposition would come from Frazer Nash, Allard and Healey.
Despite an early collision with a spinning Jowett Javelin, Leslie Johnson drove the white Jabbeke record car to victory. He finished 5.6 seconds ahead of Peter Walker who placed second in the sister XK120.
Third spot went to the Frazer Nash High Speed of Norman Culpan (the only other driver to finish on the lead lap).
Bira’s Jaguar span out of the race when a tyre blew.
1950 Palm Beach Road Race
After the good publicity achieved by winning at Silverstone, William Lyons agreed to send chassis 670001 to the USA for Leslie Johnson to contest a road race around the streets of Palm Beach on January 3rd 1950.
The event was originally supposed to take place around Florida’s Palm Beach Shores, but last minute problems meant it had to be relocated to a new 2.1-mile circuit on nearby Singer Island.
The 35 car field included another four XK120s in addition to MGs, Healeys, Allards, a Ferrari 166 Inter and some extraordinary specials to include Briggs Cunningham’s Cadillac-powered Healey and George Huntoon’s Ford-Duesenberg.
By lap twelve of the 50 lap race, Johnson was up to second. However, the tight and twisty circuit meant his brakes soon began to fade which allowed Cunningham’s Healey Special and George Rand’s Ferrari to get through.
Victory went to the Ford-Duesenberg Special of George Huntoon.
Johnson finished fourth overall and third in class. He also collected a trophy for best performance by a British car and another for best production car.
After the race, chassis 670001 was sold to a privateer (Jack Rutherford).
For the rest of the year, Leslie Johnson raced a new car (chassis 660040).
XK120 Semi-Works Competition
Johnson’s new car was one of six alloy-bodied Semi-Works Competition XK120s.
Ostensibly, these significantly uprated cars were privateer machines, but Jaguar provided considerable assistance to ensure they stood the best chance of success.
The factory-supported owners were Leslie Johnson (chassis 660040), Nick Haines (chassis 660041), Peter Walker (chassis 660042), Clemente Biondetti (chassis 660043), Ian Appleyard (chassis 660044), Tommy Wisdom (chassis 660057) and Peter Whitehead (chassis 670002).
The Semi-Works Competition cars (covered in more detail separately) achieved a host of fine results during 1950.
Leslie Johnson finished fifth at the Mille Miglia and looked set for a potential win at Le Mans until clutch failure forced him to retire while lying third.
Elsewhere, Peter Walker won the Silverstone 1 Hour Production Car race and Ian Appleyard took victory on the Alpine Rally. Stirling Moss won the Dundrod Tourist Trophy in Tommy Wisdom’s car.
Moss and Johnson then teamed up to set a series of speed records at Montlhery where they most notably averaged 107.6mph over 24 hours.
Privateer Racing Cars
True privateers were also quick to test their XK120s in competition. Perhaps the best known was a young Phil Hill who campaigned chassis 670138 which he most notably used to win the Pebble Beach Cup.
Move to Steel Bodywork
In May 1950, the first predominantly steel bodied XK120 rolled off the production line.
Only the hood, doors and bootlid remained aluminium. Pressed steel moulds enabled the firm to dramatically increase production, but there was a 51kg weight penalty.
XK120 FHC
In March 1951, Jaguar unveiled a Fixed Head Coupe variant (FHC).
The FHC featured a handsome teardrop cabin profile reminiscent of a Bugatti Atalante and was equipped to a generally higher specification than the OTS roadster.
Aside from its new body configuration and lockable doors, most of the FHC’s upgrades were found in the cockpit. Burr walnut veneers were applied to the dash, door caps and window surrounds. Wind up windows were fitted along with opening front and rear quarterlights. The roof was upholstered with a fine wool headliner.
Other equipment included tinted Plexiglas sun visors, a lockable glovebox, a dash-mounted ashtray and new simplified door panels. A carpeted parcel shelf / rear bulkhead panel was fitted directly behind the seats.
Production of left-hand drive FHCs began in July 1951. Right-hand drive examples followed in November.
Wire Wheel Option
When the FHC was launched, Jaguar also introduced a new centre-lock wire wheel option for both the OTS and FHC variants. When specified, the distinctive rear wheel spats were omitted owing to insufficient clearance for the chromed Rudge double-eared knock off hubs.
XKC (C-type)
After the XK120’s promising display at the 1950 Le Mans 24 Hours, William Lyons sanctioned the development of a fully fledged sports racing version for 1951.
The resultant XKC (better known as the C-type) made its debut at the 1951 Le Mans 24 Hours. Three works cars were entered; one retired, one finished eleventh and the example driven by Peter Walker / Peter Whitehead took a famous victory.
Further wins at the Dundrod Tourist Trophy and two end-of-season races at Goodwood (all by Stirling Moss) meant the C-type finished 1951 with a 100% success record.
Special Equipment Option
June 1951 was not only significant because of the C-type’s debut; it also market the arrival of an optional SE upgrade pack for the XK120.
The SE (Special Equipment) featured a 9.0:1 compression ratio, high lift camshafts, lightweight flywheel, stiffer rear springs and a dual exhaust system.
SE variants all came with an S prefix to their six digit chassis number.
Peak output was 180bhp at 5300rpm and 203lb-ft at 4000rpm compared to 160bhp at 5000rpm and 195lb-ft at 2500rpm for the standard car.
1952 Montlhery Speed Records
Having set a number of speed records at Montlhery in October 1950, Leslie Johnson and Stirling Moss returned to France in August 1952, this time with an XK120 FHC (chassis 669002).
The car was provided by Jaguar for an attempt on the seven day record where Moss and Johnson would be joined by Bert Hadley and Jack Fairman.
Together, they averaged 100.31mph for seven days and nights covering 16,851 miles.
In addition to the overall record, five new class records and four World Records were set for shorter distances.
XK120 DHC
The final iteration of the XK120 was launched in January 1953 when Jaguar added a Drop Head Coupe to the range (DHC).
The DHC was to essentially the same specification as the FHC, but with a padded and lined canvas top that could be folded down onto the deck behind the seats.
Another new addition for 1953 was the option of chrome instead of painted wire wheels.
C-type Head Option
In April 1953, Jaguar introduced their most potent engine upgrade thus far.
The addition of a C-type head with its larger SU H8 carburettors was available only as an aftermarket item for installation by the owner or dealer.
XK120s equipped as such produced 210bhp at 5750rpm and 213lb-ft at 4000rpm.
1953 Jabbeke Speed Run
An XK120 was used for one final record attempt in October 1953 when Jaguar test driver, Norman Dewis, piloted OTS chassis 660986 to 172.4mph.
Once again, the record took place on the Jabbeke highway in Belgium and this time, the tuned XK120 had been modified with a domed single seat roof canopy from a glider.
660986 had actually been used at Jabbeke back in April 1953, when it hit 140mph. However, after a Pegaso went slightly faster a few weeks later, Jaguar decided to return and settle the matter.
End of Production
The XK120 was discontinued in 1954, by which time 12,055 had been completed. It was replaced by the XK140.
XK120 production comprised 7612 Roadsters (1175 right-hand drive and 6437 left-hand drive), 2678 Fixed Head Coupes (194 right-hand drive and 2484 left-hand drive) and 1765 Drop Head Coupes (294 right-hand drive and 1471 left-hand drive).
Roadster VINs commenced at 660001 in right-hand drive and 670001 in left-hand drive.
Fixed Head Coupe VINs commenced at 669001 in right-hand drive and 679001 in left-hand drive.
Drop Head Coupe VINs commenced at 667001 in right-hand drive and 677001 in left-hand drive.
Text copyright: Supercar Nostalgia
Photo copyright: Jaguar Heritage Trust - https://www.jaguarheritage.com/
