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"The BMC A-series engine did service in a variety of cars for almost 50 years, during which time it was available in a bewildering variety of capacities and states of tune."
Keith Adams introduces the legend, and follows it with LJK Setright’s thoughts on the subject, as first published in CAR magazine.
The A-series engine was certainly a case of the ‘British Curate’s egg’ – good in places. In fact, that is not quite true: the A-series was a fine engine. Of course, by the time of the launch of the Austin Metro in 1980, great play was made by the British press about the fact that here they had a new car, which truly competitive and as good news as it was, it was still powered by an engine that first saw service in the Austin A30 some 30 years previously. Of course, to make this criticism was to miss the point entirely.
British Leyland had expended much time and effort on the task of replacing the A-series engine, but the trouble was that it was capable of delivering fantastic fuel consumption figures thanks in no small part to its excellent torque characteristics and thermal efficiency. Because of this, the A-series became a victim of its own success: why produce a replacement, when there was doubt that anything new that was produced would be any better to drive?"
http://www.aronline.co.uk/facts-and-fig ... -a-series/

Well worth reading the 'comments section' after the A-Series engine article above where ex-BL engineer Ray Battersby reveals some of the background and engine development stories when he worked at Longbridge in the 1970's.
See extract below from one of Ray Battersby's several interesting posts on the A Series engine:-

Question from Nate:
"From what I have been able to read on the Second Generation South African A-series engine, it featured an oil filter mounted high on the block, new internal oil galleries and an integral block casting that did away with the removable tappet covers.
Engines were produced in two sizes, 1098cc (or more accurately 1097cc) and 1275cc. However, unlike the engines produced in the UK, the South African engines shared a common bore, of 70.64mm, and the displacement was altered by the stroke, meaning only the crankshaft and pistons would not be interchangeable between the two yet the same connecting rods were retained – 1098cc was achieved with a stroke of 69.85mm (compared to the long-stroke 1098cc engine found elsewhere), while 1275cc came courtesy of an 81.28mm stroke.
It caught my interest mainly because the A-OHC project on the surface at least appears to feature similar displacements and elements to the Second Generation South African A-Series including a common 70.6 mm bore.
By the way curious to know whether Eddie Maher’s improvements to the A-Series was simply limited to an All-Alloy Head (or whether it was a Crossflow, 8 Port head and something more) as well as whether any connection exists between Eddie Maher’s tuned A-Series and the MG-badged Victoria prototype with a tuned, twin-carb (83 bhp) version of the 1275cc engine?"

Answer from Ray Battersby:
Nate,
Whilst writing, may I respond to your earlier question about the 1293/1380 A-Series?
Reliability of these engines would most certainly be reduced (all other things being equal).

Let’s talk crankshaft. If you envisage looking along the length of a crankshaft you can possibly imagine the circular outlines of the main and big-end bearings. A modern, short-stroke crankshaft will use larger bearing diameters than the A-Series and looking along its length, the bearings actually overlap each other. This adds tremendous strength and durability to the crankshaft and also reduces its tendency to bend (and ultimately break) when it is supported by only three main bearings. An old style crank (such as the A-Series), with its smaller bearings and longer stroke is the opposite with no overlap whatsoever.

So when the A-Series is ‘stroked’, it exacerbates this issue by reducing the overlap of the main and big-end bearings. This is not a good move to make for any engine, especially when the crank is already made of forged steel!

Turning to the cylinder bores. From memory, the A-Series was originally designed as an 803cc capacity. In this mode, I am sure that the water passages within the cylinder block extended completely around all four cylinders. As its bore was increased over the following decades, water flow was reduced and I seem to recall that nota single cylinder of the 1275cc block had water flow completely around any of the cylinders. I have read people who say that siamesed bores are good for strength. Quite possibly but how do humans warm their hands on a cold winter’s day? We rub our hands vigorously together to create frictional heat that is absorbed by the hands.

A siamesed cylinder is no different except that we don’t want to warm up the pistons of adjacent cylinders! That leads to piston and cylinder distortion, oil passing the ring pack into the combustion chamber and potential seizures. siamesed bores also leave little room for the cylinder head gasket to completely seal adjacent cylinders. In the 1970s, 6mm of metal between adjacent cylinders was the absolute minimum for a gasket to seal. A leaking head gasket (between cylinders) completely ruins the performance of both cylinders – 50% of the total engine.

So unless a cylinder block has been designed to be bored out, the end result can only reduce reliability.

When Harry Webster first announced the H-Series engine specification to the drawing office in 1970-71, he named it the ‘dedicated’ engine. Why?

He recognised that most of the costs of solving A-Series problems had resulted from repeatedly increasing the 803’s bore and stroke over the years. He wanted the new H-Series to be dedicated to 1,000cc and we thus ensured that it could neither be bored nor stroked without manufacturing a completely new engine. We allowed just a 3mm clearance between the conn-rods and the crankcase as they swept around inside. There was simply no room to increase the cylinder bores because, much against our better judgement, all the bores were already siamesed with just 6mm between them.

Scroll down for comments section:-
http://www.aronline.co.uk/facts-and-fig ... -a-series/

Also mentioned below in one of Ray's posts.......the 3 litre Maxi!

"And before I drop off my perch, is there space here to recall the ‘3 litre’ Maxi?
This had two Maxi engines – the regular manual transmission engine up front and an automatic unit at the rear. Mini experience of double-engines (its capacity was 2,550cc altogether) taught the lesson that the driver couldn’t manage two gearboxes so he used the front gearbox and the rear engine just sorted itself out regarding gear selection.
These projects were again handled by the boys downstairs (relative to we designers in the Engineering block next to the Kremlin) in the development department overlooking the Lickey Road.
There’s still more. Around 1973 I designed a simple device to convert the E-6 engine into a variable capacity design. A 1.1 litre 3 cylinder unit for speeds up to 50mph (and sipping fuel at an incredible 50mpg) with the full 2.2 litre 6 cylinders available automatically for better acceleration and speeds over 50mph. Anybody could make this device in the garden shed today and it worked so well that nobody knew when it went from 3 to 6 cylinders. In fact I had to fit a dash-panel lamp to indicate when it was on 6 cylinders."

Good stuff!