BMC A-series engine

's small straight-4 automobile engine, the A series, is one of the most common in the world. Launched in 1951 with the Austin A30, production lasted until 2000 in the Mini. It used a cast-iron block and cylinder head, and a steel crankshaft with 3 main bearings. The camshaft ran in the cylinder block, driven by a single-row chain for most applications, and with tappets sliding in the block, accessible through pressed steel side covers for most applications, and with overhead valves operated through rockers. The cylinder head for the overhead-valve version of the A-series engine was designed by Harry Weslake – a cylinder head specialist famed for his involvement in SS engines and several F1-title winning engines. Although a 'clean sheet' design the A series owed much to established Austin engine design practise, resembling in general design and overall appearance a scaled-down version of the 1200cc overhead-valve engine first seen in the Austin A40 Devon which would form the basis of the later B-series engine.
The A-series design was licensed by Nissan of Japan, along with other Austin designs. Improvements were rapid. An early change was to incorporate a 5 main bearing crank. The cylinder head was modified for the first of the E series by swapping plugs and ports, plugs fitted between pushrods and 8 ports eliminated the Siamesed inlet and exhaust ports. Nissan modified the design into the later Nissan A engine that was launched in 1966 with an aluminium head and wedge combustion chambers. It became the basis for many of their following engines notably the later OHC Nissan E engine, was scaled up into Nissan CA engine and ultimately the DOHC CA18DET. All these engines show their lineage by the characteristic un-skirted crankcase block of the BMC A series, but with the A and E having the camshaft moved to the right side allowing greater port areas, and a mounting on the right wall of the crankcase for the oil pump whereas the BMC A series had the oil pump at the back end of the left-side camshaft.

Engine Family List

All engines had a cast iron head and block, two valves per cylinder in an OHV configuration and sidedraft SU carburettor. Engines were available in diesel in the BMC tractor.
All A-series engines up until mid-1970 were painted in British Standard 223 Middle Bronze Green. This does not include overseas production models such as Australian manufacture.

A versions


The original A-series engine displaced just and was used in the A30 and Morris Minor. It had an undersquare bore and stroke. This engine was produced from 1952–56.
1956 saw a displacement increase, to. This was accomplished by increasing the bore to while retaining the original stroke. It was produced until 1964.
YearsModelPower outputTorque
1956–62Austin A35 at 4,750 rpm at 2,000 rpm
1956–62Morris Minor 1000 at 4,750 rpm at 2,500 rpm
1958–61Austin A40 Farina at 4,750 rpm at 2,000 rpm
1958–61Austin-Healey Sprite at 5,200 rpm at 3,300 rpm
1961–62Austin A40 Farina MkII at 5,000 rpm at 2,500 rpm
1961–64Austin-Healey Sprite MkII at 5,500 rpm at 3,000 rpm
1961–64MG Midget at 5,500 rpm at 3,000 rpm


The bore was retained for 1959s Mini version. This displacement was reached by dropping the stroke to. This engine was produced through to 1980 for the Mini, when the [|998 A-Plus version] supplanted it.
YearsModelPower outputTorque
1959–69Austin Seven/Austin Mini/Morris Mini at 5500 rpm at 2900 rpm
1961–62Riley Elf/Wolseley Hornet at 5500 rpm at 2900 rpm
1963–68Austin A35 Van at 5500 rpm at 2900 rpm
1964–68Mini Moke at 5500 rpm at 2900 rpm
1969–80Mini 850/City at 5300 rpm at 2900 rpm


The one-off version for the Mini Cooper used a smaller bore and longer stroke. It was produced from 1961–1964.
The Mini also got a version. This was similar to the 948 in that it had the same stroke but the bore was increased slightly to. It was produced from 1962–92. This engine was first introduced into the Mk II versions of the Riley Elf and Wolseley Hornet, before coming common fitment in the mainstream Minis.
YearsModelPower outputTorque
1962–69Riley Elf/Wolseley Hornet at 5250 rpm at 2700 rpm
1966–82Mini Moke, Australian Mokes.
1983–93Mini Moke, Portuguese Mokes.
1964–69Austin/Morris Mini Cooper at 5800 rpm at 3000 rpm
1967–80Austin/Morris Mini at 5250 rpm at 2700 rpm
1969–75Mini Clubman at 5250 rpm at 2700 rpm
1969–80Mini at 4850 rpm at 2750 rpm


The version was fitted to:
It was a stroked version of the 998 previously used in the Riley Elf and Wolseley Hornet. It was produced from 1962–80.
YearsModelPower outputTorque
1962–66Austin A35 Van at 5100 rpm at 2500 rpm
1962–67Austin A40 Farina at 5100 rpm at 2500 rpm
1962–71Morris 1100/Morris Minor 1000 at 5100 rpm at 2500 rpm
1962–68MG 1100 at 5500 rpm at 2500 rpm
1962–64Austin-Healey Sprite MkII at 5500 rpm at 3250 rpm
1962–64MG Midget at 5500 rpm at 3250 rpm
1963–74Austin 1100 at 5100 rpm at 2500 rpm
1963–67Vanden Plas Princess 1100 at 5500 rpm at 2500 rpm
1964–66Austin-Healey Sprite MkIII at 5750 rpm at 3500 rpm
1964–66MG Midget MkII at 5750 rpm at 3500 rpm
1965–68Riley Kestrel/Wolseley 1100 at 5500 rpm at 2500 rpm
1973–75Austin Allegro at 5250 rpm at 2450 rpm
1975–80Austin Allegro at 5250 rpm at 2900 rpm
1968–82Mini Moke
1969–71Morris Mini 1100/Morris Mini K
1971–75Morris Mini Clubman/Leyland Mini
1975–80Mini Clubman at 5250 rpm at 2700 rpm
1976–80Mini 1100 Special at 5250 rpm at 2700 rpm


The version was another one-off, this time for the Mini Cooper S. It used a new bore size and the stroke from the 848. It was only produced in 1963–1964. Paired with the even rarer version, below, it became that rarest of things: an oversquare A-series engine.
The Mini Cooper S next moved on to a version. It had the same bore as the 1071 cc Cooper S but used a shorter stroke. It was produced from 1964–1965.
The largest A-series engine displaced. It used the bore from the Mini Cooper S versions but the stroke from the plain Mini Cooper. It was produced from 1964 until 1980, when it was replaced by an [|A-Plus version]. The bore size was around the maximum possible in the block, with very little separation between the middle cylinders, which often contributed to head gasket failures.
YearsModelPower outputTorque
1964–71Austin/Morris Mini Cooper S at 5800 rpm at 3000 rpm
1965-74Mini Marcos at 5900 rpm at 3000 rpm
1966–70Austin-Healey Sprite MkIV at 6000 rpm at 3000 rpm
1966–74MG Midget MkIII at 6000 rpm at 3000 rpm
1967–68MG 1300/Wolseley 1300 at 5250 rpm at 3000 rpm
1967–68Riley Kestrel 1300 at 5250 rpm at 3000 rpm
1967–68Vanden Plas Princess 1300 at 5250 rpm at 3000 rpm
1967–73Morris 1300 at 5250 rpm at 3000 rpm
1967–74Austin 1300 at 5250 rpm at 3000 rpm
1967MG 1275/Riley 1275 at 5250 rpm at 3500 rpm
1967Wolseley 1275 at 5250 rpm at 3500 rpm
1967Vanden Plas Princess 1275 at 5250 rpm at 3500 rpm
1968–69Riley Kestrel 1300/Riley 1300 at 6000 rpm at 3000 rpm
1968–71Austin America at 5250 rpm at 2500 rpm
1968–73Wolseley 1300 at 5750 rpm at 3000 rpm
1968–73MG 1300 MkII at 6000 rpm at 3000 rpm
1968–74Vanden Plas Princess 1300 at 5750 rpm at 3000 rpm
1968MG 1300/Riley Kestrel 1300 at 5750 rpm at 3000 rpm
1969–71Morris 1300GT at 6000 rpm at 3250 rpm
1971–82Mini Moke Californian Australian only.
1969–74 at 5300 rpm at 2550 rpm
1969–74Austin 1300GT at 6000 rpm at 3250 rpm
1971–80Morris Marina at 5250 rpm at 2500 rpm
1971Austin Sprite at 6000 rpm at 3000 rpm
1973–80Austin Allegro at 5300 rpm at 3000 rpm
1974–80Mini 1275GT at 5300 rpm at 2550 rpm

A-Plus versions

was keen to update the old A-series design in the 1970s. However, attempts at replacement, including an aborted early-70s Rover K engine and an OHC version of the A series, ended in failure. During the development of what would become the Austin Metro, engineers tested the A series against its more modern rivals and found that it still offered competitive fuel economy and torque for its size. While in the 1970s the A series had begun to seem dated against a new generation of high-revving overhead cam engines, by the end of the decade a new emphasis on good economy and high torque outputs at low speeds meant that the A series's inherent design was still well up to market demands.
Given this, and the lack of funds to develop an all-new power unit, it was decided to upgrade the A-series unit at a cost of £30 million. The result was the 'A-Plus' Series of engines. Available in, the A-Plus had stronger engine blocks and cranks, lighter pistons and improved piston rings, Spring loaded tensioner units for the timing chain and other detail changes to increase the service interval of the engine. More modern SU Carburettors and revised manifold designs allowed for small improvements in power without any decrease in torque or fuel economy. Many of the improvements learnt from the Cooper-tuned units were also incorporated, with A-Plus engines having a generally higher standard of metallurgy on all units, where previously only the highest-tuned engines were upgraded in this way. This made the A-Plus engines generally longer-lived than the standard A series, which had a life between major rebuilds of around in normal service. Studies were made into upgrading the engine to use five main crankshaft bearings but the standard three-bearing crank had proven reliable even in high states of tune and at high engines speeds, so it was not deemed worth the extra funding.
The new engines received distinctive 'A+' branding on their rocker covers and the blocks and heads were colour-coded for the different capacities: yellow for and red for engines.

998 Plus

The A-Plus version of the motor was produced from 1980–92.
YearsModelPower outputTorque
1980–82Mini 1000/City/HL at 4750 rpm at 2000 rpm
1980–82Austin Allegro at 5250 rpm at 3000 rpm
1980–90Austin Metro at 5400 rpm at 2700 rpm
1982–88Mini HLE/City E/Mayfair at 5000 rpm at 2500 rpm
1981–86Austin Metro HLE
1988–92Mini City/Mayfair at 5250 rpm at 2600 rpm

1275 Plus

The larger engine was also given the "A-Plus" treatment. This lasted from 1980–2000, making it the last of the A-series line.
YearsModelPower outputTorque
1980–82Austin Allegro at 5600 rpm at 3200 rpm
1980–84Morris Ital at 5300 rpm at 2950 rpm
1980–90Austin Metro at 5650 rpm at 3100 rpm
1982–89MG Metro at 6000 rpm at 4000 rpm
1983–85Austin Maestro HLE at 5500 rpm at 3500 rpm
1983–93Austin Maestro at 5800 rpm at 3500 rpm
1984–89Austin Montego at 5600 rpm at 3500 rpm
1989–90Austin Metro GTa at 6000 rpm at 4000 rpm
1990–91Mini Cooper at 5550 rpm at 3000 rpm
1990–91Mini Cooper S at 6000 rpm at 3250 rpm
1991–96Mini Cooper 1.3i/Cabriolet at 5700 rpm at 3900 rpm
1991–96Mini Cooper S 1.3i at 5800 rpm at 3000 rpm
1992–96Mini Sprite/Mayfair at 5000 rpm at 2600 rpm

1275 Turbo

To allow the MG Metro to compete with larger, more powerful hot hatchbacks a turbocharged version of the A-Plus was developed with the assistance of Lotus Engineering. A Garrett T3 turbocharger was fitted along with a unique SU carburettor with an automatic pressure-regulated fuel system. The engine block, cylinder head, pistons, crankshaft and valves were all modified from the standard A-Plus engines. The turbocharger was fitted with an advanced two-stage boost control system which only allowed full boost to be achieved at engine speeds above 4000 rpm - this was to prevent damage to the sump-mounted four-speed gearbox, the design of which dated back to the early 1950s and could not reliably cope with the high torque output of the Turbo engine at low speeds. The quoted power for the A-Plus Turbo was although in practice the tune could vary from car to car and, because the engine was not intercooled power varied significantly depending on the weather. The MG Metro Turbo was entered in the British Touring Car Championship in 1983 and 1984, with the tuned engines producing in excess of.
Turbo versions lasted from 1983–90.
A special "twin-port injection" version of the engine was developed by Rover engineer, Mike Theaker. It was the last A-series variant, produced from 1997–2000. Few changes were made to ensure the engine complies with Euro 2 emission standard, such as adding a 3-way catalytic converter and making it twin-point injection, the engine also receive changes with ignition system by having a wasted spark instead of the distributor. For the Japanese domestic market. the engine maintained the single-point injection version of the engine and the radiator is still on the side due to the space constraint for the air conditioner component.
During the 1990s Mini Cooper revival, John Cooper Garages offered a number of factory-approved "Cooper S" and "Cooper Si" upgrades to the standard Coopers. The conversions came with a full Rover warranty, and could initially be fitted by any franchised Rover dealer.

Diesel Version

The diesel version appeared in 1962, on the BMC Mini tractor. It was developed with the help of Ricardo Consulting Engineers. It was redesign of existing 948 cc version, new purpose-designed cylinder head, with Lucas CAV fuel injection. This engine has dry liners. The block is almost identical to the petrol engine. The oil pump has been removed from the camshaft and is driven by an extension to what would have been the distributor drive. It uses Ricardo-patented "Comet V" combustion chambers, with a compression ratio of 23.6:1. Produced 15hp at 2500rpm and torque at 1,750 rpm. A petrol version of this modified engine was 'reverse-engineered' for use in the Mini Tractor whilst retaining parts commonality with the diesel variant, rather than using a standard petrol A-series unit. The diesel A series was also sold as a marine engine under the BMC name alongside the diesel B-series engines. Production ceased in 1969.

South African engines

At the end of 1965, BMC South Africa started a new program, with the aim of using more components manufactured in the country. They decided to develop and manufacture their own version of the engine. Two versions were made with 1.1 and 1.3 litres, using the same cylinder block. The block was redesigned, new oil circulation arrangements and redesigned main bearing and stronger/biffers camshafts. Both versions use the same connecting rods, but different crankshaft and pistons. Prototypes versions were made by 1969. Production began in 1971, ending in 1980.

OHC version

With the intention of updating the current engine, for use in the new Mini Clubman, and current ADO16, Leyland developed an OHC version. It appeared in a prototype version in 1971, with single overhead camshaft. It featured redesigned cylinder block, new aluminium cylinder head and twin SU carburetors. Eleven prototypes units were built, in three different capacities, 970, 1070 and 1275 cc. All engines use the same cylinder bore dimension of 70.6 mm, to reduce the number of engine parts, reducing production costs. It uses a modular modular approach, making it possible to produce the three versions with the same engine block. The lack of investment and the turmoil and chaos in British Leyland, meant the engine never reached production. In 1975 the plan was abandoned in favour of the "A+" version that reached production in 1980.

Twin cylinder A-series

Under the code ADO11, the twin cylinder was build with the intention to be used in ADO15. The it was based in 948cc unit, already in use by BMC. It has 474cc, with single H2 SU carburetor, and already has sump gearbox, FWD layout, that will be used in the Mini. In May 1957, the engine was tested in one Austin A35, along side another "prototype", 500cc, two-stroke, this one was tested in one Austin A30.

Current use

This engine continues to be improved, it has a very large and wide market, whether this is classic car industry or racing industry. It has a wide OEM manufacturer support. Almost every part of the engine is still made, whether in original specification or improved versions, pistons, camshafts, crankshafts, cylinder heads. Cylinder heads are available in 8v or 16v, made in aluminium with 5 or 8 ports.
The A series engine is used in David Brown Mini Remastered. The engine is totally rebuilt, with new internals to a improved specification. The engine used is based in 1275cc MPi version.