100- 4 1953-55
Production of the Austin-Healey 100, designated the BN1 series, started at Longbridge in May 1953. A four-cylinder 2660cc engine similar to the one fitted in the Austin A90 Atlantic powered the new Healey and drove the 100’s live rear axle through what had started out in life as an A70/90 four-speed gearbox. Only three of the four forward gears were ‘live’ in the version fitted to the BN1; the selector on first gear being omitted due to the ratio being deemed too low for a powerful sports car. Originally designed for column change, the ‘box’s selectors were situated to one side, resulting in the 100’s floor gearchange being angled to exit the left-hand side of the transmission tunnel.
The 100’s chassis was a very advanced structure for the time; the main members consisted of two rectangular boxes braced centrally by a cruciform structure. Mountings on the end of a pair of front transverse crossmembers incorporated fixings for the front dampers. Four body-mounted outriggers were welded in pairs each side of the chassis’ main members, while at the rear substantial crosspieces connected a pair of body mounting legs. The 100- 4’s immensely strong and rigid chassis/frame set up remained largely unchanged throughout the big Healey’s production run.
Although pre-production 100 bodies were made of aluminium, once BN1 production moved to Longbridge the car’s wings and doors were changed to steel pressings produced by Jensen Motors. However, a small number of early Longbridge-built Healey 100- 4’s retained pre-production aluminium bonnets and boot lids, although all versions were fitted with alloy front and rear shrouds.
BMC introduced the BN2 Austin-Healey 100 in 1955 and although the revised sports car still retained the earlier car’s four-cylinder engine and twin SU carburettor set up, the 100- 4 now was equipped with a stronger, fully functioning four-speed gearbox. Despite the ‘box still being designed for column-change, the gear lever now exited the transmission tunnel almost centrally and the revised gearshift was now a conventional four-shift pattern.