Press Release
Technical Highlights of the MINI Classic.
The original MINI Classic entered the market in 1959 with a four-cylinder power unit. This engine dated back to the year 1951, when the Series A power unit was featured for the first time in the Austin A30 and the legendary Morris Minor. The crankshaft rotated in three bearings, the four combustion chambers of this original engine displacing a total of 803 cc and developing maximum output of 28 hp.
The overhead valves were driven by pushrods and a camshaft beneath the engine on the same side as the intake and exhaust ducts.
The longitudinal-flow cylinder head had heart-shaped pockets in the combustion chambers accommodating the valve openings and spark plugs. This ensured excellent distribution of the fuel/air mixture in a very turbulent process for optimum fuel combustion and running smoothness.
High-speed engine concept: 34 hp at 5, 500 rpm.
When development of the MINI Classic started and Issigonis was looking for an appropriate power unit, the Series A engine had already been updated once. The new engine now displaced 948 cc and maximum output was 37 hp. With this being too much for the chassis and brakes of the small MINI Classic, capacity of the engine now fitted crosswise was reduced by 100 cc and output cut back to 34 hp at 5,500 rpm.
This gave the engine unusually high running speeds, with only thoroughbred sports engines, for example in a Jaguar, revving up to continuous speeds of this kind back then. After several increases in engine size, the use of other carburettors, and ultimately the introduction of fuel injection, the last versions of the original MINI Classic displaced 1.3 litres and developed maximum output of up to 63 hp.
New developments in front-wheel-drive technology.
Beneath the engine Issigonis entered unchartered technical terrain, for the first time placing the gearbox beneath the engine and directly between the wheels, meaning that the engine and gearbox shared the same oil circuit. This left enough space at the front of the car for the radiator fitted at the side as well as the steering and ancillary units. Even so, the MINI Classic’s front-wheel-drive concept still required BMC’s engineers to look at a number of features, with the transmission of power to the wheels remaining a weak point: The universal joints still used back then tended to warp under severe movements of the steering, significantly impairing the car’s driving behaviour.
To solve this problem, Issigonis’ team decided to use homokinetic joints instead, a technology never used before in an automobile. These joints were made up of a ball bearing surrounded by three cages, two of which were connected with the incoming and outgoing drive shafts.
This design allowed a sufficient steering angle without exerting a major influence on the car’s steering and driving behaviour. To reduce the forces acting on the light and compact body, the engineers mounted the entire drivetrain, steering and suspension on a sub-frame. And since the independent rear wheels were also mounted on a sub-frame, the MINI Classic benefited from excellent directional stability.
Simply ideal: rubber springs.
The MINI Classic’s suspension was a highlight in technology from the start. Instead of coil, torsional or leaf springs, Alec Issigonis gave the MINI Classic rubber springs made up of two cones with a layer of rubber in between.
The upper cone was bolted firmly to the sub-frame, the lower cone rested on the wheel mount.
With rubber becoming increasingly hard as a function of pressure, this gave the MINI Classic progressive spring action. Indeed, the qualities of the spring system were so good that small telescopic dampers were quite sufficient. To ensure a fine and smooth response, the dampers were fastened on the outside to the upper track control arms up front and to the rear longitudinal arms at the back.
Built-in self-levelling: Hydrolastic.
In 1964 Issigonis presented yet another outstanding solution in suspension technology, carrying over the new Hydrolastic suspension from BMC’s larger saloons to the MINI Classic. The characteristic feature of this unique suspension was the cylinders on each wheel roughly the size and shape of a one-litre can of oil. This cylinder accommodated both the springs and dampers, with an anti-freeze water emulsion serving as the damper fluid. The particular highlight of the Hydrolastic system, however, was the connection of the hydraulic chambers on each side of the front and rear wheel dampers by pressure pipes. On the road this meant that if the front wheel went over a bump, part of the hydraulic damper unit was pressed into the “partner” chamber on the rear axle, slightly lifting up the body of the car in the process. And naturally, this also worked the other way round.
While this system kept the car at the same consistent level in theory, it involved significant disadvantages in practice: Whenever the passengers sitting on the rear seats of a MINI Classic were relatively heavy and the luggage compartment happened to be fully laden, the rear end dropped down and as a result lifted up the front end of the car. So it was almost inevitable that Hydrolastic was discontinued in the MINI Classic in 1971.
140 kilos of pure lightweight technology: the body-in-white.
The bodyshell of the MINI Classic was a wonderful example of lightweight engineering: Although the body-in-white weighed a mere 140 kilos or 309 lb, the metal structure offered a degree of torsional stiffness quite unique at the time. This was ensured in the longitudinal direction by the two sills and a small tunnel in the middle of the car housing the exhaust pipes, as well as the wheel arches. In a crosswise direction, it was the robust bulkhead between the engine compartment and the passenger cell, a crossbar beneath the front seats and the luggage compartment bulkhead which likewise helped to ensure superior stiffness.
This high standard of all-round stability even allowed the use of slender roof pillars with large windows. And, after 32 years, it was also this stiffness that provided the option to develop and build a Convertible.
