Engines : A-Plus Series

Britain’s commonest engine, the ubiquitous A-Series, has earned a place in history for its frugality, adaptability and the sheer weight of its success.

LJK Setright said it deserved its new lease of life with the launch of the Austin Metro. First published in CAR magazine 1980.


A-Plus – powering the mighty Metro

Metro GTa

In its final form, they called it the A-Plus. It is the engine which, to the surprise of all of us and the disappointment of the less realistic among us, was chosen to power the new Metro, crux of BL’s survival and recovery.

It is also, apparently, the engine which powered the Austin A30, that appallingly unlovely and deservedly unlamented little saloon which was the firm’s first unitary-construction job and which, appearing in 1952 as the first fruit of the new liaison between Austin and Morris to form the BMC, looked as though its slab-sided narrowness might have resulted from being pressed out between them.

In fact, it is not the same engine. The principles, the ideas, and even much of the layout, remain unchanged after the passage of nearly 30 years and some millions of Austin Sevens, Morris Minors, Minis, Midgets, Sprites, Allegros, Coopers and capers. The bits are different, though: not a single part is interchangeable between the latest engine and the original one.

Indeed, it is probably a pity that the rocker-box pressing of the latest A-Plus looks just like that of the previous versions: there are people in BL who reckon that the man in the showroom would have been more impressed by the Metro had that most familiar part of the engine been changed.

Changes to make it the A-Plus

So much revision was made of the engine in preparing it for the Metro – higher compression ratios, stiffer block, new cams and manifolds, better valve materials, and a whole heap of details starting at the air filter and ending at the crankdamper – in a £30m development and retooling programme, that BL might easily have got away with recoding it, as the K-Series, say (the elements of A can form K if rearranged), and everybody would have been happy.

The engine performs well enough, after all: dynamometer test comparisons between the A-Plus and comparable engines from other manufacturers in various parts of the world left no doubt that it was fit to drive the Metro into the 1980s, especially in view of its very low specific fuel consumption. If, instead of accusing them of conservatism, one credited BL with conservationism, their guiding principles might be better recognised.

Few people criticise Renault for working along the same lines: its little four-cylinder engine, which could be regarded as the other leading economy engine in Europe, is even older, stemming from the 1948 4CV.

Do not make the mistake of thinking that the A-Series was kept in production just because it is a very simple engine which is therefore very cheaply made. In fact, it is rather costly to make, having been designed to suit manufacturing and assembly procedures that are a good deal more laborious than those by which more fashionably modern engines are produced.

A-Series engine’s exotic materials

Some of its materials are expensive, too: a nitriding steel enables the crankshaft journals to be hardened beyond the probability of wear, a Nimonic alloy gives the exhaust valves the high-temperature stability and creep-resistance enjoyed by the blades of the aviation gas turbines for which it was first compounded, Stellite (a cobalt alloy) faces and preserves the exhaust valve seats in the 1275cc version.

Such good stuff is not commonly to be found in engines that could be called common, as the A-Series can. It may be argued that costly materials and elaborate manufacturing procedures (for instance, the fillet-rolling which toughens the crank journals) are made necessary by the essential crudity of the basic design.

There is some justification for this view as it applies to some of the many high-performance sporting variants that sparkle against the subfuse of three decades, for the extravagant employment of superior materials and craftsmanship has traditionally been the method whereby the silk purse of the circuits has been made out of the sow’s ear of the suburban streets.

This sort of thing has been going on since the early days of the original 803cc engine, which soon spread from the A30 to the Minor. When that engine grew to 948cc for the A35 (by means of bigger and siamesed bores, a thinner gasket to cure distortion, thicker crankpins and lead-indium shells to cure big-end failure, and shorter main bearings to allow stiffer crank webs – the large-diameter main journals were always robust enough for anything), only a few obvious tuning tricks were necessary to fit it for the Austin Healey Sprite which followed in early 1958.

Developing the original A-Series

It was this 948cc engine which, with its stroke shortened to cut the capacity down to 848cc. was turned athwartships to power the original Mini. With a drive gear and clutch between the rear main bearing and the flywheel, the crankshaft was longer and more susceptible to torsional vibration – not a problem in the original 850cc Mini but one that calls for a damper on later faster or longer-stroke crankshafts.

While the Sprites sensationally performed on the big rallies such as the Alpine and the Marathon, the Mini began its competition career more tentatively. Early cars had little done to them, but it was noteworthy that a Don Moore cylinder head soon replaced the Weslake design.

Neither the Competitions and Special Tuning Departments of BMC nor the mainstream engine designers lacked developmental skills, but some outsiders played a significant part in making the A-Series engine wax strong and kick. Perhaps most important of these was Daniel Richmond of Downton Engineering: his powerful, torquey and economical 1071cc variation was greatly admired by Sir Alec Issigonis and formed the basis of the S-type Mini-Cooper.

A racing start

The earlier Cooper engine, a 997cc unit, grew from a surprisingly effective Formula Junior racing engine for which BMC’s Engineer Maher probably deserves most of the credit; but it was the Cooper S, sanctioned for production by engines chief Appleby although it was almost too good for a production car, which was the highpoint of the A-Series development story. First as a 1070cc and then as a short-stroke 970cc with longer conrods and a long-stroke 1275cc with a taller block, the Cooper S was prodigiously effective and astonishingly durable.

All manner of supertuning tricks were played on it, and I still remember the shattering performance of the Equipe Arden car which I drove at the end of the 1967 season after Steve Neal had proved it the fastest Mini in racing. In simplified form the 1275 was a giant-killer in Spridgets, too, and the Special Tuning demonstration car thrilled me with its 118mph performance and its inadequate brakes, while the real racers got up to as much as 140.

Sometimes the engine was fitted with fuel injection, sometimes (and to very good effect) with Amal motorcycle carburettors;  sometimes it was supercharged, sometimes turbocharged (the British Vita team were experimenting with this as early as 1966), and often it was simply overstressed.

Almost infinite variety

The variations of 30 years’ production and competition could not be digestibly listed in less than a book – there were at least 20 different camshafts produced by the factory prior to the Metro development – nor all the people involved named. All these things and all those people were largely responsible for the A-Series becoming the standby of racer, rallier, show-off and shopper. Not many people worried about how many camshafts or where; they just satisfied themselves that the engine could be made to do almost any specific job.

Cutaway drawing of the 848cc A-series complete with transmission-in-sump, as it first appeared in the 1959 Mini.
Cutaway drawing of the 848cc A-Series complete with transmission-in-sump, as it first appeared in the 1959 Mini

Some of these jobs were far removed from the original intention, so it was only to be expected that the list of detail changes was commensurately long, demanding good hands, decent tools and occasionally a rather deep purse. It was thanks to the utter simplicity of the basic design that these changes could be made; that simplicity was a function of the original terms of reference for the design.

The priorities in the late 1940s, those years of austerity and hope, were economy, reliability, and ease of putting into production. The other two are explicable, but how do we explain the economy? I have pointed out before that it is not the metal of an engine, but the holes it encloses, which determine how well it breathes and burns and turns energy into work; and in the A-Series engine, the crucial hole was in the head.

Weslake was overrated

There have been times when I thought the work of the late Harry Weslake rather overrated, but the combustion chamber that he designed for the original 803cc engine was almost certainly the secret of its success and, adapted no more than was necessary, that of the success of all subsequent production variants. It may not have been right for power; in fact it was decidedly unsatisfactory without a good deal of metal removal and reshaping.

It was right for what was wanted: very smooth and very economical part-throttle running with minimal ignition advance. The wheel has come full circle. After the frenzied search for performance in the great Monte Carlo days of the mid-1960s, that phase of 15 years’ attack has been followed by another phase of 15 years’ retrenchment: we are back where we started, with priorities that as ever include reliability and ease of putting into production but see economy as the foremost item on the list. The sort of engine that we and the Corporation wanted in 1951 is just the sort that we and the Company want in 1981.

Now it is Plus a bit, and minus nothing but the glamour, for many of the features of the Metro engine that I mentioned earlier were special to the erstwhile Cooper S. Many more are refinements of the sort that competition in sport overlooks, but that competition in the market place (and therefore in the engineering offices) can foster: such things as the much stricter carburation, the much more carefully controlled and consistent ignition, are what allow the compression ratio and the thermal efficiency to go up while the fuel quality is coming down. But it still does not really matter how many camshafts there are, nor where.

Old-fashioned? So is virtue.

LJK Setright
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1 Comment

  1. Iconic engine, doing the job but so outdated in 1980 ! Long-stroke, all-iron-steel, OHV, non-cross-flow, 3 bearings ! Yes Renault would still produce its Billancourt till 1986 but the last new car to use was the Renault 5L launched in 1972.

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