Austin Healey 100/4

1953–1956 · 14,634 built · the four-cylinder car

Two and a half litres of Austin saloon engine, a body by Jensen, and a gearbox with first gear blanked off.

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About the Austin Healey 100

The BN1 went on sale in May 1953 with the 2,660cc overhead-valve four out of the Austin A90 Atlantic, 90bhp on twin SU 1.5in carburettors, and one of the odder gearboxes of the period: the A90 four-speed with first gear blanked out, giving three speeds with overdrive on second and top. 10,030 were built. In August 1955 the BN2 replaced it with a genuine four-speed box, overdrive on the top two, slightly larger front wheel arches and a different rear axle — 4,604 of those, the 100M included. Suspension is independent wishbone and coil at the front, live axle on semi-elliptic leaves at the rear, and the brakes are Girling 11in drums all round on every one.

“100M” needs establishing before you order. The factory car got 1.75in carburettors, a cold air box, a high-lift camshaft, 8.1:1 pistons, stiffened front suspension and the louvred bonnet with its leather strap — 110bhp, and 640 built between September 1955 and July 1956. Separately, about 500 Le Mans engine kits were sold to dealers and owners, fitted with the engine in the car, giving nearer 100bhp. So a car wearing 100M badges may be a factory car, a period kit car or a modern replica, and the three do not need the same parts. The 100S is a different animal again: hand-built at Warwick, February to November 1955, all-aluminium body, Weslake alloy head, 132bhp, no hood or bumpers — 50 production cars plus five works prototypes, and the first British production car with disc brakes on all four wheels.

Austin Healey 100 — specification & changes within the model

BN1: May 1953 – August 1955, 10,030 built. 2,660cc Austin A90 four, 87.3 × 111.1mm, 90bhp @ 4000rpm, twin SU 1.5in semi-downdraught.
BN1 gearbox: Three speeds plus overdrive on second and top — the A90 four-speed with first gear blanked out. Not a true three-speed box.
BN2: August 1955 – July 1956, 4,604 built including the 100M. Genuine four-speed, overdrive on the top two. Slightly larger front wheel arches and a different rear axle.
Brakes: Girling 11in (279.4mm) drums all round, on every 100. No 100 has discs except the 100S.
Suspension: Independent double wishbone and coil front; live axle on semi-elliptic leaf springs at the rear.
100M: 640 factory-built, 5 September 1955 – 16 July 1956. 110bhp @ 4500rpm from 1.75in carburettors, cold air box, high-lift cam, 8.1:1 pistons and stiffened front suspension, with the louvred bonnet and leather strap. About 70 per cent were two-tone.
Le Mans kits: About 500 sold separately to dealers and owners, fitted with the engine in the car, to a BN1 or a BN2. Around 100bhp — less than a factory 100M. A 100M badge is not proof of anything; the 100M Registry certifies them.
100S: February – November 1955, hand-built at Warwick. 50 production cars plus five works prototypes. All-aluminium body, Perspex screen, no bumpers, no hood, around 200lb lighter. Weslake alloy head, 132bhp @ 4700rpm, twin SU H4 1.75in, four-speed with no overdrive. Dunlop discs front and rear — the first British production car with four-wheel discs (the Crosley Hotshot of 1949 beat it worldwide).
Bodies: By Jensen Motors, West Bromwich. Early cars aluminium; steel panels came in before regular Longbridge production began in May 1953.
Note on this search: The All Austin Healey 100 Parts button searches 100/4. Plenty of big-Healey parts suit the 100-Six and the 3000 as well — if you do not see what you need here, try those pages too.