Austin 7 Technical Specifications

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Austin 7 Technical Specifications
Austin 7

The most popular pre-war car ever made, the halcyon days of the Austin 7 covered two decades, survived the austere depression years and remained the affordable alternative to the large and expensive cars of the day.

  • Years of Manufacture: 1922 - 1939
  • Number Built: 290,000+ (worldwide)
  • Price at Introduction: n/a
  • Chassis/Body:
    • Seperate chassis, A frame style with engine mounted between the stroke channel divisions at the narrow front end
  • Exterior Dimensions:
    • Total Length: n/a
    • Total Width: n/a
    • Total Height at kerb weight: n/a
    • Wheelbase: 6 ft. 3in.
    • Front Track: 40in.
    • Rear Track: 40in
  • Kerb Weight:
    • 794 lb.
  • Fuel Tank: n/a
  • Turning Circle: n/a
  • Transmission:
    • To 1933: 3 speed manual, no synchromesh
    • From 1933: 4 speed manual, with synchromesh to 3rd and 4th gears
    • 1934: Synchromesh added to second gear
  • Clutch:
    • Single cushion disc, dry plate clutch
  • Rear Axle Ratio:
    • Spiral bevel type, with ratio's between 4.4:1 and 5.6:1
  • Maximum Speed:
    • n/a
  • Fuel Consumption:
    • n/a
  • Performance:
    • n/a
  • Engine - 4 Cylinder:
    • Capacity: 747cc
    • Type: Side-valve, watercooled four stroke, reciprocating piston type with 4 cylinders, pressure lubricated crankshaft, aluminium crankcase and cast iron cylinder block and head
    • Configuration: Front mounted, driving rear wheels
    • Head: Cast iron
    • Fuel System: Single downdraft type carburettor
    • Bore and Stroke: 56mm x 76mm
    • Power:
      • 1922 Model: 10.5 bhp (7.8 kW) approx
      • 1933 Model: 17 bhp (12.7 kW) approx
    • Torque: n/a
    • Compression Ratio: n/a
  • Ignition and Electrical:
    • Electric starter motor introduced in 1923
    • Magneto system replaced by coil type in 1928
  • Exhaust:
    • Single tail-pipe
  • Suspension:
    • Front: Beam axle with centrally mounted half elliptic transverse spring
    • Rear: Cantilevered from the rear of the chassis via by quarter elliptic springs
  • Steering:
    • Worm type
  • Brakes:
    • Front: Drum
    • Rear: Drum
    • Note: Early models operated the front brakes via the handbrake control and the rear via the footbrake, rather than in unison
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Herbert Austin

History records Herbert Austin was a bluntly spoken but considerate boss with an impressive command of Black Country swear words. He knew little about engineering theory and was seldom seen to make any calculations. His engineering was based on experience and instinct but, because he was more often right than wrong, his judgment was respected by the more highly qualified people under him. Austin's design philosophy was simple - make it work and make it work reliably. His manufacturing policy was fundamental - build it in the factory (so no one shares the profit) and cut out unnecessary frills and complications.

Austin's engineering education began in Australia. In 1884 as an eighteen year old, he came to live with an uncle in Melbourne and joined the firm importing Crossley engines. After some years, he took a job in a foundry to widen his engineering experience. The next step was to join the Wolseley Sheep Shearing company, where his ingenuity in mechanising sheep shearing procedures was reported to the English parent company. This led to an invitation to return to England and supervise the production of sheep shearing machines. By 1900, Austin was working on motor cars. One year later, he was appointed manager of Wolseley's new car division. The company's first product, a fragile looking machine with a horizontally opposed engine, led to a fine line of vehicles and a rapid growth in sales.

Austin personally designed the early cars and enthusiastically supported a motor sport program. It is little wonder that when he left to put up his own shingle above an abandoned factory at Longbridge, near Birmingham, he brought an abiding interest in racing. Austin produced a series of strong, reliable, undistinguished tourers. Apart from the years spanning World War One, his firm did not prosper and in 1921 the Austin Motor Company was close to bankruptcy.

The Austin Seven Saves The Day

Austin was one of the few Englishmen of his day who thought that a market existed for a small car that was light on fuel and easy to drive. He studied the small European cars and decided that the company's future lay in the mini car field. The official receiver, who was then managing the company disagreed and refused to authorise any such expenditure. Never a man to take no as an answer, Austin commenced work in secret. To create a drawing office, he converted the billiard room at his home in the nearby Lickey Hills. He brought in a seventeen year old draughtsman Stanley Edge, and several technical advisers. This was just as well, for these men steered Austin past a few eccentric ideas which might well have scuttled the project.

Austin's first idea was to power the baby car with an air-cooled, twin-cylinder, horizontally-opposed engine. After some discussion, he abandoned the idea and began drawing up a three-cylinder radial engine to be placed at the rear of the chassis. Edge talked him out of this. Austin also considered an early Sunbeam idea of having the four wheels in diamond formation — one at each end of the car and two in the middle. Eventually, though, he decided to scale down a perfectly orthodox chassis layout. Edge set about drawing up a conventional four-cylinder 700 cm3 engine, using the larger Austin 20 hp unit as the model. The design followed established Austin practice, with a cast iron block and cylinder head, side valves and an alloy crankcase.

Austin experimented with a three-bearing crankshaft design, but finally settled for two bearings, using the Peugeot idea of a roller bearing at the back and a ball race at the front. When the drawings were complete, Austin had the parts made in the factory and a prototype assembled. The little car, with no running boards and an all-up weight of only 330 kg greatly amused the people at the plant. But when Austin - complete with bowler hat - took the wheel and scorched up the Lickey Road hill, some grins changed to looks of admiration. The little car really went very well. Its 700 cm3 engine developed 10 hp at 2400 rpm. The back axle ratio was low (4.9 to 1) and, combined with the low vehicle weight, it gave very good top gear performance.

An Impromptu Drag Race

Austin was so delighted with the tiny car's acceleration that he staged an impromptu drag race with one of his 20 hp tourers. The Seven was quicker off the mark. For all the excitement, the official receivers didn't want a bar of the new car. Austin threatened to quit the Austin Motor Company, and start a new firm to manufacture his baby. He set a production target of 300 cars a week - a figure most people thought ridiculous. Somehow he managed to convince the Board that he could sell this number and the venture would be profitable. Because Austin owned the design - not the company - the Board agreed to pay him two guineas (A$4.20) royalty on each car produced.

Production eventually reached 500 a week, with a total output of 291,000 Sevens in England. Thousands more were built under licence in France and Germany. The American version, called the Bantam, was a commercial failure and neither Herbert Austin nor the company received royalties from them. Despite a design which made good engineers wince, the Seven was a brilliant success. Even by contemporary standards, the steering, braking and road holding were abominable, and it was said at the time that a benevolent providence watched over all Austin Seven occupants. The car succeeded initially because it could be bought for 50 Pounds down and 10 Pounds a month in repayments.

Motoring for the Masses

This brought motoring within the reach of thousands of professional and semi-professional people. Most had no previous driving experience and they cared little about the niceties of wheel adhesion, steering accuracy or unsprung weight. But the engine started easily and reliably, it used half or less than half the fuel of bigger machines and rumbled along at a steady 60 km/h (37 mph). In England, a Seven cost only eight Pounds a year in tax, against 23 Pounds for a Model T Ford. The basis of the design was an A-shaped chassis frame with outriggers. To this was bolted (without rubber mountings) a well proportioned four-cylinder engine of 696 cm3 (later 747 cm3), coupled to a three-speed crash gearbox. Between them stood a single plate clutch with a quarter inch effective movement and such an abrupt action that kangaroo-hopping became a way of life for inexperienced drivers.

The gearbox drove a rear axle, via a torque tube, the axle being located by only two quarter elliptic springs and a ball joint at the end of the torque tube. As a result, it was seldom at right angles to the chassis frame. Not that this made much difference, as the frame twisted so much that the wheels could not stay at right angles to the road surface. The front axle was sprung on a transverse leaf spring. The steering was incredibly direct - and even when the king-pins were unworn it took a masterful hand to steer a straight line. Herbert Austin is reputed to have said that good brakes encouraged bad driving. No doubt his desire to improve the standard of driving led to the adoption of a most primitive system in the Seven.

Design Changes

The rear brakes were cable operated by the foot pedal. The separate front brake system, controlled by the hand brake lever, had the unnerving habit of operating unasked when the front wheels were turned on full lock. As the front and rear brakes operated independently, it was normal practice to use the foot pedal and the hand brake lever simultaneously. If the driver had a spare hand for gear changing, a quick heel-and-toe into a lower gear helped peel off speed more effectively than the brakes themselves.

As the years went on, the chassis design improved in detail, but the basic concept remained unchanged for 15 years. Austin switched from magneto to coil ignition, then the front and rear brakes were coupled and, on occasions, with this improved system you could really feel them trying to slow down the car. The gearbox got an extra gear and even the engine was updated with a third main bearing. Power from the standard engine increased slowly from 10 to 17 hp but the sports models and supercharged engines gave much, much more depending on the state of tune.

Also see:

Austin Seven Review | The History of Austin | Herbert Austin | The Austin Seven in MotorSport
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