Big Healeys


The original car, known as the Healey 100, was built as a prototype in 1952. It was aimed at a gap in the market between the ageing MG “T” Type and the up market Jaguar XK range. It was known that Austin were looking for a new sports car at the time and this probably influenced Donald Healey’s choice of components used in the design. The car made it’s debut at the 1952 Earls Court Motor Show and by the end of that week a deal was struck between Donald and Leonard Lord for Austin to produce the car as the Austin Healey 100.



As an engineer, Geoffrey Healey was aware of the importance of a stiff chassis for good handling, and for it’s time the Healey chassis was quite good. It is a ladder type chassis constructed from hollow rectangular section members; two main longitudinal members with a cross member front and back, and a strong cruciform section just behind the gearbox. Outriggers behind the front wheels and in front of the rear wheels are connected to inner sills add significantly to the torsional rigidity of the chassis.

Welded to the top of this chassis is the tub, a sheet metal inner body, floor, A and B posts. This time it is the bulkhead around the transmission tunnel that adds strength to the chassis. The body and trim panels are mounted on the tub. The doors, bonnet and boot lid are in steel, whilst the bonnet and boot surrounds (shrouds) are in aluminium.


The AH 100 engine is a 2600cc four cylinder unit from the Austin A90. This engine has its origins in trucks and lived on for many years in London Taxies. It is long stroke, low revving unit with loads of torque.

The AH 100-6 engine is a four main bearing, six cylinder unit from the Austin Westminster, and contrary to popular opinion does not have it’s origins in truck manufacture. Initially at 2600cc, this was enlarged to 2900cc for the AH 3000 requiring a new block in the process. Early 100-6 engines had the inlet manifold cast into the head making the engine very inefficient. On the road this car was slower than it’s 100 predecessor. The head was changed to a 12 port design which was retained through into the AH 3000 engine. At the same time, the connecting rods were changed from clamped little ends to fully floating gudgeon pins. This combination enabled the engine to rev more freely.


With the torque of the A90 engine but less weight, first gear was too low to be of any use so the selector mechanism was modified to disable first gear. This gave a 3 speed box with overdrive on the top two ratios. A stronger, revised gearbox was introduced with the BN2, and this utilised all four ratios. These gearboxes were from column change saloon cars with the result that the floor change conversion emerged from the left hand side of the gearbox. During the reign of the 3000 MKII, the gearbox was modified to a centre change with the lever emerging from the top. The Laycock overdrive was retained as an option throughout.


Drum brakes were used on all four wheels until the introduction of the AH 3000 when discs were fitted to the front.



Like MGs, the Healey is well catered for when it comes to spares ref. the links page. With the exception of engine block, gearbox casing and back axle casing it is possible to build a new car, at a price!

On the chassis, outriggers, inner sills and lower wings are prone to rust. The main chassis rails are less prone to rust but can; from the bottom on UK cars due to road salt, and from the top on “dry State” cars due to lost hoods and wet carpets. Replacing these is a skilled job best undertaken on jigs. As the chassis becomes weak it will sag, resulting in the door gaps closing up at the top. A good sound car will always have even door gaps of about 3 to 4 mm

Word has it that body panels were mixed and matched on the production line to get a reasonable fit. It follows therefore, that replacement panels rarely fit without modification and repairing the original panels is usually the preferred option.


The engines are conventional and easy to restore. 100 owners often opt to upgrade the engine to 100M specification. This was a factory fitted tuning pack comprising camshaft, HS6 carburettors and higher compression pistons which raised the output to about 115 BHP. 100-6 and 3000 cars can benefit from the last of the line BJ8 camshaft. Power was gradually increased from 124 BHP on the 3000 MKI to 150BHP on the 300MKIII (BJ8), mainly from camshaft changes. With further camshaft and exhaust system changes, 170 BHP is quite common with little loss of tractability. Another myth is that the triple SU carburettors on the MKII are difficult to tune; they are not and they stay in tune, and are no less economical.


With the exception of the early 3 speed cars, the gearboxes are tough. They often only require stripping, cleaning and rebuilding with new bearings and synchro cones. The overdrives do get tired; the pump, accumulator and pistons start to leak, and they become slow to engage especially when hot. A rebuild is usually best left to a specialist.

The rear axles are very tough and go on forever. The bits that may wear are the pinion taper roller bearings.


Steering boxes are available on an exchange basis and many suppliers will exchange a LHD for a RHD at little or no extra cost. This done, all that remains to convert a car’s drive from one side to the other is the steering idler pivot casting, throttle pedal and a dashboard. Brakes, clutch and instruments are transferable and all the fixing holes exist.


Overall, the big Healeys are well made cars and provided that they are maintained in good condition are very reliable. Fuel consumption, provided that the car is not fitted with triple Webers, should be in the mid 20s miles per gallon(UK).

There is also a world wide network of clubs with both social and competition event calendars to make Healey driving a very enjoyable experience.


  • 100 BN 1, 1953-55: two-seater roadster, three-speed plus overdrive.
  • 100S, 1955: Racing 100 with Weslake-type cylinder head and all-round disc brakes.
  • 100 BN2, 1955-56: two-seater, four-speed plus overdrive.
  • 100M, 1955-56: 100 upgraded to Le Mans spec.
  • 100-6 BN4, 1956-59: 2+2 seating, 2600cc six, length extended by 6.5in & wheelbase extended by 2in.
  • 100-6 BN6, 1958-59: two-seater roadster, same wheelbase as 2+2.
  • 3000 Mk I BN7, 1959-61: two-seater, 2900cc, front discs in place of drums.
  • 3000 Mk I BT7, 1959-61: 2+2, otherwise same as the BN7 Mk I.
  • 3000 Mk II BN7, 1961-62: two-seater, triple 1.5in SU carbs in place of twin 1.75in, revised grille.
  • 3000 Mk II BT7, 1961-62: 2+2, same changes as BN7 above.
  • 3000 Mk II BJ7, 1962-63: 2+2 convertible with curved screen, quarter lights, winding windows and folding hood.
  • 3000 Mk III BJ8 Phase 1, 1963-64:2+2 with new dashboard, folding panel behind rear seats, twin 2in carbs.
  • 3000 Mk III BJ8 Phase 2, 1964-68:2+2 with improved ground clearance and anti-tramp bars.