THE BIRTH OF THE A-SERIES

Bill Appleby, who was later to become chief designer of engines and gearboxes for BMC, was the leader of the engine design section at Longbridge. Although he was in charge, and must take much of the credit for steering the ship in the right direction, it is clear that most of the detailed design and layout for the new Seven engine was carried out by his deputy and successor, Eric Barcham. Indeed, most of the instructions that Eric received came direct from the chief designer, Johnnie Rix.

War was still raging when Eric laid down the preliminary dimensions for a new, 7 hp side-valve engine. In fact, it was June 1942, a date drawn from the notebooks in which he calculated the various fits and limits of the engines on which he was working. Later in the same year, an overhead-valve version of the 8 hp side-valve engine was laid out, but it was never built.

Experiments were also carried out with a three cylinder engine that had been produced from the 8 hp unit. They had a devil's own job trying to balance it, though. According to Bill Appleby, 'When the gear-lever knob vibrated in resonance with the engine, the knob could scarcely be seen.'

By the mid-1940s, however, Len Lord had just about made up his mind that all future Austin engines should be of overhead-valve design. That he wavered a little before deciding on an ohv unit for the A30 was quite understandable. If it was to be a true successor to the pre-war Seven, simplicity and cheapness were essential considerations.

A look at Eric Bareham's notes shows that on 24 May 1949 a side-valve engine was still in the running. On that date he detailed a design specification for an SF (small four) 7 hp, 800 cc side-valve engine, for which it was stipulated that weight and cost should be kept to a minimum. To this end, it was proposed that thermosyphon cooling be used and that the distributor be placed on the front of the block to eliminate the need for a camshaft skew gear, A question mark was placed against the need for a petrol pump, although it seems that gravity-feed was never considered too seriously. It was also suggested that further economies could be made by combining the oil filler and dipstick, and by using the dynamo and starter motor from the A40. It was not long, however, before this proposed engine was abandoned.

In the end, of course, the A30 was to borrow much more than the odd ancillary from the A40's 1200 cc ohv engine. The unit was proving so popular and reliable that it seemed sensible to consider basing the new engine on a scaled-down version, the cost of which would fall somewhere between the £28 for an A40 engine and an estimated £18 for a new 7 hp side-valve unit.

By July 1949, the preliminary fits and limits had been calculated for an 800 cc overhead-valve engine which was to bear a close resemblance to the larger A40 unit. This meant it was to be a conventional four-cylinder, inline unit, but by careful attention to detail, the designers hoped to achieve considerable gains in efficiency. The team was hoping to achieve these gains without forsaking the Austin tradition of producing an engine that was very flexible over a wide speed range and that pulled well, even at low revs. Much thought was to be given to the features that produced these characteristics: a comparatively heavy flywheel, large valves and well-researched valve timing. During its design period, it was to be known simply as the 7 hp or AS3 engine. lt was only much later that it became known as the A-series.

The A40 engine had been such a success that it was decided to employ the same stroke/bore ratio of 13: 1, using a stroke of 76 mm and a bore of 58 mm. As this ratio was slightly higher than normal, it helped to minimize the engine's length. The water pump helped in that respect too; it was designed so that its rotor lay inside the cylinder block.

A great deal of the credit for the efficiency of the engine must be attributed to the cylinder-head design, which had been evolved by Harry Weslake. Most of the cylinder heads of the period were of simple 'bathtub' design, hut Weslake's philosophy was to 'look after the gas'. His cylinder heads incorporated a heartshaped combustion chamber which directed the incoming gas towards the plug. A high gas velocity was maintained into the chamber by running the wall of the chamber very close to the back of the inlet valve. This also created considerable swirl, which seemed to stratify the charge and give a richer mixture near the plug, leading to more efficient burning and improved fuel consumption. Zenith, the manufacturers of the carburettor, remarked several times that combustion in this little engine was more constant than in any other they were testing at the time.

Dr John Weaving, who was in charge of research and development at Longbridge, gleefully recalls how they tried to improve on Weslake's design by cutting off the protuberance in the combustion chamber, familiarly known to them as the'Weslake tit'. Try as they might, they had little success, since any alterations tended to cause pinking. Eric Bareham points out that Weslake's design features determined not only the shape of the combustion chamber, but also the valve-port shapes-a point not usually recognized.

John Bishop, who was responsible for the stressanalysis work that was done on the engine, had also developed the cam profile. The shape of the cams had been determined mathematically. The idea was to produce a cam that eliminated any sudden changes in acceleration of the entire valve mechanism while a valve was opening or closing. This reduced wear on the moving parts and, at the same time, permitted higher valve lift and better engine breathing. The part of the cam profile which takes up the clearance between the tappet and the end of the valve stem is known as the ramp. Bishop designed this so that at the point of contact between the tappet and the end of the valve stem, the ramp would only be moving at about a third of the velocity of a conventional ramp. This resulted in extremely smooth valve operation, but it is worth noting that if the tappet clearances are not adjusted correctly, the velocity at the point of opening or closing may well be three or four times the design speed.

As with the earlier ohv Austin engines, the camshaft and pushrods were on the same side of the engine as the inlet and exhaust ports. This gave rise to nicely-placed, well-cooled spark plugs, but to avoid passing the pushrods through the water jacket, or through the ports themselves, siamezed inlet ports and a siamezed centre exhaust port had become necessities. Bill Appleby's contention was that while a siamezed exhaust port did call for fitstclass exhaust-valve materials, they never found any disadvantage in using a siamezed inlet port. In fact, he claimed it to be an advantage because the reduced volume of the induction system allowed for a quicker response to the accelerator.

Another bonus of the design was that all the electrical equipment, including distributor, plugs, starter motor and dynamo, was on the opposite side of the engine to the carburettor. This kept any potential sparks away from possible petrol drips as well as removing all the electrical gear from the heat of the exhaust manifold.

Even the exhaust heat was put to good use. With both the inlet and exhaust manifolds on the same side of the engine, it was a simple matter to produce an inlet-manifold 'hot-spot'. Thus the fuel mixture would vaporize more readily and endow the engine with its quick-warm-up characteristics.

The oil pump was unconventional, being driven from the end of the camshaft. The reason for this was to eliminate the cost of providing an extra gear to drive it, but it did mean that the pump was well above the oil level in the sump and required priming after an engine strip-down. Bill Appleby was unhappy about this arrangement, but Johnnie Rix insisted that it was a necessary economy. In fact, the pump has proved to be very successful, and you could not have a cheaper or neater assembly. A threaded plug in the crankcase wall could be removed to prime the pump after an engine rebuild, although later pumps were found to provide about a 3 ft lift when dry, so the priming plug was omitted from the design. An attempt had been made to phase the rotors of the pump in relation to the cams so that they had a damping effect on camshaft vibration.

Another point worthy of note, even though it was standard Austin practice, was the use of four rings per piston. The three compression rings, in conjunction with a lower oil-control ring, were found to give very satisfactory oil consumption and kept blow-by to a minimum. In later years, this must have been instrumental in helping the engine cope with the increasing legislation on pollution.

Once under way, the design work progressed speedily. By late 1949, components that had been made from experimental drawings were beginning to appear from the machine shops. In early 1950, a start was made on assembling the first engine. The end of March saw the engine completed and installed on a test-bed. Over the next month or two, other engines were completed and, like the first, they were subjected to endurance runs of 100 hours to test the crankshaft bearings as well as the valve gear and all the ancillaries.

Max Oliver, then in the experimental department, remembers how Alf Depper had asked him to assemble the first AS3 gearbox by handing him a box of bits and saying, 'I'd like you to put that together, Max.' There were no drawings or build instructions - in that department you had to know how to go about things and were expected to check on the fits and limits as a matter of course. Apparently, it went together with very little trouble, and in Max's words: 'George Coates had just returned from one of his merry trips abroad, so the pair of us put the gearbox on to one of the first AS3 engines and installed it in the old 8 hp. It was quite impressive - something we'd never felt before, and it was a much better gearbox.' George has his own memory of that same occasion: 'Well, it was nice to be able to set the tappets without getting your knuckles burnt. Ah, yes, that was another advantage of the overhead-valve engine.'

Eric Bareham's notes inform us that the engine for the first car was completed on 24 November 1950, and five days later it was installed in an A30 prototype.

The very earliest engines, including the one fitted to this first prototype, had an aluminium cylinder head, but the production version had a cast-iron head. Cast-iron was chosen not only because it was a familiar and reliable material, but also because it avoided any problems that might have occurred as a consequenee of fitting valve-seat inserts to an aluminium head.

Weslake suggested the use of pistons with a concave crown to ensure a compact combustion space with its largest dimensions at the centre of the piston. This alteration in design meant that the compression ratio would have dropped to less than 7:1 if the original aluminium head had been fitted, and to 6.77:1 if the standard cast iron Weslake head had been used. This was too low, but as only poor petrol was available at the time, the compression ratio could only be raised to something like 7.2:1. This was achieved by using a Weslake cast-iron head that produced a total combustion-chamber volume of 32.3 cc. The calculations required for this head are noted in Eric Bareham's diary of 19 December 1950, and it would seem that this arrangement, along with the concave pistons, was used from engine number seven onwards.

As the bench tests continued and the early prototypes were put through their paces, one or two weaknesses began to show up which necessitated small changes in the design. At a meeting in Johnnie Rix's office in February 1951, it was decided to stiffen all the crankshaft webs and to increase the size of the bearings. The main bearings were increased from the original 1 5/8 x 1 in. to 1 3/4 x 1 1/8 in., and the big-end bearings were increased from 1 3/8 x 3/4 in. to 1 3/4 x 3/4 in.

In August 1951, this engine, known as the Type II, was given 100 hours of bench testing, cycling from 2800 to 4800 rpm. At the end of the test, the con-rod bearings were found to be in bad condition and the centre main bearing was also badly worn. It was decided that a satisfactory solution would be to increase the width of the main bearings from 1 1/8 in. to 1 3/16 in., and the size of the con-rod bearings from 3/4 in. to 7/8 in. during the first continental road test of the A30 at the end of November 1951, Johnnie Rix had complained from the South of France that the sump was hitting the ground on rutted roads. He requested that it be raised by 1 in.

In May 1952, an engine that was stripped after covering 35,000 miles showed signs of wear in both the oilpump driving pin and spindle. This led to an increase of 1/32 in. in the diameter of the driving pin, giving more width to the flat. The limits on the pin and pump-spindle slot were tightened to reduce the backlash that was thought to be adding to the wear, The slot in the pump spindle was also shortened to reduce any tendency for it to open out. At the same time, the oil-pump cover was stiffened because leaks had been occurring due to distortion of the cover when it was being tightened.

In production form, the engine developed 30 bhp at 4800 rpm, and it was clear that there was plenty of scope for development. lt was to prove a remarkably efficient engine - even at its launch it was producing 75 per cent of the A40's horsepower, yet weighed 33 per cent less, even though the dynamo, starter and distributor were the same for both cars.

Most small cars of the day were still being turned out with primitive side-valve engines (which, in Ford's case, would carry on for almost a further decade), so this brand-new ohv unit was a considerable factor in the new car's favour.

Few could have guessed, however, that the engine developed for the A30 (and those derived from it) would rank as one of the greatest small engines ever produced. Its history runs through a long series of Austin, BMC, BMH, BL, Austin Morris and Austin - Rover cars: from the A30/35 and Minor, through the A40 Farina, Sprite, Midget and Mini, on to the 1100, 1300, Allegro and Marina, and finally (in its A-Plus form) to the Metro, Maestro and even the smallest Montegos of 1984. With this pedigree, we can see why the late Bill Appleby, shortly before his death, was prepared to agree that perhaps he and his designers 'had just about got it right'.

(Chapter 2 from the book: )