What made the success of the Jowett Jupiter in the 1950s especially notable was that this classic British sports-car was in production for only three years, during which time only 850 were built. And although it was based on the Jowett Javelin family saloon, it was not designed by Jowett’s engineers. Yet it continues to have an enthusiastic following among members of the Jowett Car Club.
It depended for its power-unit on the Jowett Javelin, that advanced 11/2-litre car which Gerald Palmer had designed during the war years and which enlivened the British motoring scene when it was put on the market in 1947, one of the few truly-new productions then available. Palmer had seen and admired the pre-war Lancia Aprilia (which I regarded then as the finest small closed car there was) and the six-seater Javelin had something in common with the sleek Italian saloon, in its smooth low-drag lines, interesting suspension (in the case of the Jowett using torsion-bars) and a push-rod overhead-valve flat-four engine with the radiator behind it to keep the bonnet low.
Unfortunately this unconventional car had more than its share of teething troubles. While the concept provided for seating within the wheelbase, a low centre of gravity and a top speed of 75-80 mph, with 28-32 mpg., big-ends and main bearings were liable to fail, oil-thirst was excessive and gaskets blew. Charles Grandfield, the Chief Engineer, had much work to do!
In fact, before Javelin production commenced, extensive bench and road-testing had taken place, at first using a Bradford back-axle in the prototype, then American and later Salisbury axles. The 1200cc engine was discarded and the 1486cc unit concentrated on. Its original 10mm sparking plugs were changed to 14mm and improved breathing increased power from 40 to 50 bhp. The new cast-iron cylinder-heads were a Weslake mod, and after trying cast-iron and alloy crankcases the latter was adopted, split vertically so that tie-bolts could strengthen it. A revised exhaust system showed a power increase of 1.5% and a drop of only 3 bhp with the silencers in place, and it obviated using “handed” cylinder-heads.
There was much experimentation, too, with bearing materials. Eventually lead-copper big-ends on a crankshaft of 512/530 Brinell hardness stood up to 50 bhp at 4750 rpm in spite of the higher oil temperatures a flat-four engine entailed. The original two-bearing crankshaft had been superseded by a three-bearing one. This caused problems with oil-swirl in the crankcase, and it proved a long task to correctly position a baffle to cure this.
The split crankcase prevented the oil-pump being mounted on a bearing-cap, so it was transferred to the timing-case and driven from the crankshaft by a shaft which also drove the now-vertical ignition distributor, formerly driven from the camshaft. Oil pipes were enlarged and oil-pump capacity increased, to give 65 instead of 50 lb/sq in pressure. The relief-valve exhausted below sump level and was later by-passed to the oil-pump. By 1952, after competition work had proved its worth, an oil cooler was used. Finally located between fan and radiator, this resulted in audible pulsations until the dirt-trap holes in the big-end caps were eliminated! Thus were difficulties caused by the compact bearings and higher oil-heat of a flat-four engine ironed out.
Despite the use of Zero-lash hydraulic tappets, noise from the valvegear was too high and new cam-forms were evolved, after tests using a noise-meter connected to an oscilloscope had recorded the result by cathode-ray. Mathematical calculations were made of valve seating under valvegear deflections. Alas, hydraulic tappets ceased to be available, and the noise level was never entirely satisfactory.
Camshaft and tappet materials were experimented with and five variations of piston/liner combination were tried until a Javelin (tested for its own purposes by the Avon Tyre Co) returned 3700 mpg of oil and 0.002in bore-wear after 80,000 miles at an average speed of 37-39 mph. The 1-3-2-4 firing order of the Javelin engine produced its own worries, of weak mixture to the front cylinders and noise, but the Zenith carburation was made to work satisfactorily, after Jowett had made its own bafflebox, carried in the alligator bonnet. So noise-sensitive were the Bradford engineers that they changed the fan-shaft supporting stays from flat to tubular, to cut down air-whistle over them. Gasket blowing was cured by increasing the asbestos content, which solved the trouble until engines were hotted-up for competition work.
This sorting-out process produced an engine powerful and reliable enough for a sports-car to be envisaged. It has sometimes been stated that the Jupiter was the first production sports Jowett. This is not true. In 1928 the Bradford company, which had been in business since 1906 with its economy cars, decided to introduce a sports edition of its famous 7hp model with the fiat-twin water-cooled power unit (“the little engine-with-the-big-pull”). A low radiator was moved back behind the front axle, a low-sided pointed-tail two-seater body was fitted, and gear and brake levers were external. JJ Hall helped promote the new model by using a very similar Jowett to break the Class G (1100cc) 12-hour record at Brooklands, at 54.89 mph, in spite of delays due to gasket trouble, the 907cc car’s best lap being at 66.56 mph.
Up north the Hepworth brothers, who made piston-rings, raced a similar sports Jowett, and in Croydon an agent offered the sports wire-wheeled Jackson-Jowett (the others had artillery wheels), one of which Miss Victoria Worsley used for Brooklands highspeed trials. At this time Jowett had an “ad man” who devised very good layouts, and he proclaimed the arrival of the new 1928 sports model by suggesting to “the lads of the high road and also the lassies of the beret” that they look at this Jowett, which was “as slick and trim and dare-devil as a submarine-chaser” with “a clean clipper air”. There was a lot of leg-room with the reclined position, and the engine may have been mildly-tuned because 60mph was guaranteed. All for £145!
By 1949 Jowett had decided to make another sports-car. But Palmer had left for the Nuffield scene, Roy Lunn replacing him, and the project was postponed until it blossomed as a contract for ERA at Dunstable, where Leslie Johnson would produce a chassis for a tuned Javelin engine. Professor Eberan von Eberhorst, of Auto-Union racing car fame, was given the job of designing the tubular chassis, which was displayed as an ERA-Javelin at the 1949 Earls Court Show.
The frame proved too weak, and six more ERA prototypes were made to effect improvements. However, when production of what was now the Jupiter commenced, it was at the Bradford factory. That was in 1950 and that time, to their great credit, the company had begun to race Javelin Jupiter cars, learning as they did so.
To obtain the required power for Jupiter, the Javelin engine had its cr raised from 7.25:1 to 8:1 by using piston-crowns. Ports and heads were polished and the Delaney Gallay oil-cooler fitted. 26mm Zenith 30VIG carburettor replaced 23mm one, until a Zenith 30VM proved easier to tune. The nine pint sump was retained with more room under the car, the exhaust piping had an easier run.
Output was now 60 bhp at 4750 rpm and torque 82lb ft at 3100 rpm. Overheating in the Alps caused the bonnet to be louvred and the radiator to be increased in size. Noise being of less moment, Vokes air-cleaners were dispensed with, but AC filters were later fitted. The fan-mounting was modified, but this did not prevent one puncturing the radiator of Becquart’s Jupiter on the 1952 Monte Carlo Rally.
The production Jupiter used the Javelin four-speed gearbox and transmission (but with ratios of 16.25, 9.9, 6.25 and 4.56:1 instead of 17.4, 10.6, 6.7 and 4.875:1) and the tubular chassis had a 9in-shorter wheelbase, at 7ft 9in. There was rack-and-pinion steering and the two-seater body, at first without a boot-lid, was steel-skinned over the steel framing. Weight was about 181/2 cwt unladen; height was 4ft 8in, length 13ft 7in.
After delayed production and more teething troubles, the Jupiter surfaced in 1950. But with the long-established Jowett Company in financial trouble, it lasted only until 1952-53, and the MkIII engine intended for it was not ready until early 1953. This being the case, the racing achievements of the Jupiter are rather noteworthy, even if we confine outselves to the TT and Le Mans.
Hadley and Wise were first and second in their class in the 1951 TT, and at Le Mans in 1950 the Wisdom/Wise Jupiter beat Aston Martin’s record by 14 miles in winning the 11/2-litre class of the 24-hour race. In 1951 and 1952 Becquart/Wilkins again won the class, before Porsche took over . . .
The later sports-racing Jupiter, the R1, had restyled, lighter bodywork; but the racing R4 did not survive beyond the prototype stage. Of production Jupiters, the Mk1 gave may to the Mk1A (with openable boot) in 1952.
Motor Sport had one of the first three production Jowett Jupiters for road test, and I remember it as a comfortable, rather cramped car, with an excellent hood which could be pulled over the seats without having to stop. At the time it cost £1086 17s 3d with purchase-tax. On the 8.1cr it was said to give 60.5 bhp at 4500 rpm, and some lappery of the Brands-Hatch short-course recorded speeds in the gears of 25, 421/2, 69 and 88 mph. It did 0-60 mph in 17 seconds, 0-70 in 29 seconds.
The Dunlop ventilated wheels were shod with Goodyear 5.500 16 tyres. I thought the steering-ratio too low, at three-turns lock-tolock, but liked it otherwise, although some vibration was transmitted there and through the floor. Tail-slides were easily corrected in spite of rather worn back tyres, and the Woodhead Monroe-damped suspension worked well, not always the case on a short-wheelbase light-car.
The bench seat was a bit hard, the accelerator very stiff and tending to stick but I thought the Girling hydro-mechanical brakes excellent. The gear-shift was disappointing and the pedal positioning prevented “heeling-and-toeing,” but what a smooth, willing engine! The Jupiter cruised at almost 60 mph at 3500 rpm, oil at over 50 lb, water-heat at under 50C.
We got to know this unusual sports-car on a night run to see the Torquay Daily Express Rally. Mostly it was enjoyable, but the 10-gallon fuel tank was too small, the hood let in rain, the body rattled, the windows were stiff to wind up, the lower gears whined, and at over 60 mph wind-noise became excessive. The speedometer also read terribly fast, and this car (GKY 106) had no boot lid.
After running Javelins, Motor Sport’s Managing Director decided to get a Jupiter, an early car (HAK 268). I was riding in it when it was being taken back to Bradford for servicing, when there was an almighty “bang” and a dent appeared in the bonnettop. The fan had torn away, severing wires and rendering the starter inoperative! On the run back to Essex after repairs, the big-ends ran and, when that was put right, at 4500 miles a gasket blew. The front tyres also wore out quickly, due to incorrect tracking.
But in the end all was cured, and this red Jupiter covered more than 25,000 in 12 months and was declared to be most enjoyable and easily able to average over 50 mph, with good economy. Which must be why this unconventional British Classic is still enthused over in 1989. WB