BMC A-series engine

The Austin Motor Company A-series is a British small straight-4 automobile engine. 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 three 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 blocks are not interchangeable between versions intended for conventional end-on mounted gearboxes and the 'in-sump' transaxle used on British Motor Corporation/British Leyland front wheel drive models such as the Mini. 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 (Jaguar) engines and several Formula One-title winning engines. Although a "clean sheet" design, the A-series owed much to established Austin engine design practice, resembling in general design (including the Weslake head) 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.

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 (381c) 223 "Middle Bronze Green". This does not include overseas production models such as Australian manufacture. "Factory/dealer warranty replacement" units were painted black, these were primarily distributed for the failures common to the "wet crank" primary gear system in early Minis.

{| class="wikitable"

! colspan="10" |Petrol

!ID

! scope="col" |Displacement

! rowspan="14" |A

! scope="row" |

!1951–1956

|||||7.5:1|| rowspan="3" |Single H2 / Zenith 26JS or 26VME||||4800|||| 2400

! scope="row" |

!1959–1980

| rowspan="2" |||||8.3:1||||5500|||| 2900

! scope="row" |

!1956–1964

|||8.3:1||||4750|||| 2500

! scope="row" |

!1964–1967

|||

|<nowiki>-</nowiki>

| rowspan="2" |Twin HS2||||6500|||| 3500

! scope="row" |

!1961–1964

|||

|8.3:1||||6000|||| 3600

! scope="row" |

!1962–1980

|||||8.3:1||Single HS2||||4750|||| 2700

!998 cc (60.9 cu in)

!1964–1971

|64.58 mm (2.543 in)

|76.2 mm (3.00 in)

| -

|Twin HS2

|55 PS (40 kW; 54 hp)

|5800

| 57 lb.ft (77 N.m)

| 3000

! scope="row" |

!1963–1967

||||| rowspan="2" |8.5:1||Twin HS2||||6000|||| 4500

! scope="row" |

!1962–1980

|||||Single HS2||||5200|||| 2450

!1962–1968

| -

|Twin HS2

|55 PS (40 kW; 54 hp)

|5500

|2500

!1971–1980

| -

! scope="row" |

!1964–1971

|||||8.8:1||Twin HS2||||5300||||3000

!1967–1980

| -

|Single HS4

|5300

|3000

!1968–1974

| -

|Twin HS2

|6000

|3000

! rowspan="6" |A+

!998 cc (60.9 cu in)

!1980–1992

|64.58 mm (2.543 in)

|76.2 mm (3.00 in)

| 9.4:1

|Single HIF38

|5250

|3000

!1980–1992

| 9.75:1

|Single HIF44

|5600

|3200

!1983–1990

| 9.4:1

|Single HIF44 / Turbo

|6130

|2650

!1992–1996

| 10.1:1

|SPi

|5500

|3000

!1996–2000

| 10.1:1

|MPi

|5500

|3000

!1992–2000

| 10.1:1

|SPi / MPi

|5800

|3000

! colspan="11" |Diesel

!947 cc (51.7 cu in)

!1962–1969

|62.9 mm (2.48 in)

|76.2 mm (3.00 in)

|23.6:1

|Lucas CAV

|15 PS (11 kW; 15 hp)

|2500

| 1750

A versions

803

thumb|Austin A35 van engines, original 948cc left, replacement 803cc right

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 to 1956.

Applications:

1952–56 Austin A30, at 4400 rpm and at 2200 rpm
1952–56 Morris Minor Series II, at 4800 rpm and at 2400 rpm

948

1956 saw a displacement increase, to . This was accomplished by increasing the bore to while retaining the original stroke. It was produced until 1964.

{| class="wikitable"

|+Applications

! Model !! Power output !! Torque

| Austin A35 || at 4,750 rpm || at 2,000 rpm

| Morris Minor 1000 || at 4,750 rpm || at 2,500 rpm

| Austin A40 Farina || at 4,750 rpm || at 2,000 rpm

| Austin-Healey Sprite || at 5,200 rpm || at 3,300 rpm

| Austin A40 Farina MkII || at 5,000 rpm || at 2,500 rpm

| Austin-Healey Sprite MkII MG Midget|| at 5,500 rpm || at 3,000 rpm

848

thumb|right|250px|An 848 cc A-series engine in a 1963 Austin [[Mini]]

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.

{| class="wikitable"

|+Applications

! Model

! Years !! Power output !! Torque

| Austin Seven/Austin/Morris Mini

| 1959–69 || rowspan="4" | at 5500 rpm || rowspan=5| at 2900 rpm

| Riley Elf/Wolseley Hornet

| 1961–62

| Austin A35 Van

| 1963–68

| Mini Moke

| 1964–68

| Mini 850/City

| 1969–80 || at 5300 rpm

997

The one-off version for the Mini Cooper used a smaller bore and longer stroke. It was produced from 1961 to 1964.

Applications:

1961–1964 Austin/Morris Mini Cooper, at 6000 rpm and at 3600 rpm

998

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 to 1992. This engine was first introduced into the Mk II versions of the Riley Elf and Wolseley Hornet, before becoming common fitment in the mainstream Minis.

{| class="wikitable"

! Model

! Years !! Power output !! Torque

| Riley Elf/Wolseley Hornet

| 1962–69 || at 5250 rpm || at 2700 rpm

| Mini Moke, Australian Mokes.

| 1966–82 || rowspan="2" | ||rowspan=2|

| Mini Moke, Portuguese Mokes.

| 1983–93

| Austin/Morris Mini Cooper

| 1964–69 || at 5800 rpm || at 3000 rpm

| Austin/Morris Mini

| 1967–80 || rowspan="2" | at 5250 rpm || rowspan=2| at 2700 rpm

| Mini Clubman

| 1969–75

| Mini (automatic)

| 1969–80 || at 4850 rpm || at 2750 rpm

1098

The version was fitted to:

MG Midget Mk1 1098cc, Oct 19621964
MG Midget Mk2 1098cc, 1964–66
Austin A35 Van 1098cc, 1962–68
Austin A40 Farina Mk2, Oct 19621968
Morris Minor, Oct 19621971
Austin/Morris BMC Saloon from 1962
Mini and its derivatives, the 1098cc engine mounted transversely

It was a stroked (to ) version of the 998 previously used in the Riley Elf and Wolseley Hornet. It was produced from 1962 to 1980.

{| class="wikitable"

! Years !! Model !! Power output !! Torque

| 1962–66 || Austin A35 Van || rowspan=3| at 5100 rpm || rowspan=3| at 2500 rpm

| 1962–67 || Austin A40 Farina

| 1962–71 || Morris 1100/Morris Minor 1000

| 1962–68 || MG 1100 || at 5500 rpm || at 2500 rpm

| 1962–64 || Austin-Healey Sprite MkII || rowspan=2| at 5500 rpm || rowspan=2| at 3250 rpm

| 1962–64 || MG Midget

| 1963–74 || Austin 1100 || at 5100 rpm || at 2500 rpm

| 1963–67 || Vanden Plas Princess 1100 || at 5500 rpm || at 2500 rpm

| 1964–66 || Austin-Healey Sprite MkIII || rowspan=2| at 5750 rpm || rowspan=2| at 3500 rpm

| 1964–66 || MG Midget MkII

| 1965–68 || Riley Kestrel/Wolseley 1100 || at 5500 rpm || at 2500 rpm

| 1973–75 || Austin Allegro || at 5250 rpm || at 2450 rpm

| 1975–80 || Austin Allegro || at 5250 rpm || at 2900 rpm

| 1968–82 || Mini Moke (Australia only)||rowspan=3| ||rowspan=3|

| 1969–71 || Morris Mini 1100/Morris Mini K (Australia only)

| 1971–75 || Morris Mini Clubman/Leyland Mini (Australia only)

| 1975–80 || Mini Clubman || rowspan=2| at 5250 rpm || rowspan=2| at 2700 rpm

| 1976–80 || Mini 1100 Special

1070

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.

Applications:

1963–1964 Austin/Morris Mini Cooper S, at 6000 rpm and at 4500 rpm

970

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 to 1965.

Applications:

1964–1967 Austin/Morris Mini Cooper S, at 6,500 rpm and at 3,500 rpm

1275

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.

{| class="wikitable"

! Years !! Model !! Power output !! Torque

| 1964–71 || Austin/Morris Mini Cooper S || at 5800 rpm || rowspan=2| at 3000 rpm

|1965-74 || Mini Marcos || at 5900 rpm

|1966–70 || Austin-Healey Sprite MkIV || rowspan=2| at 6000 rpm || rowspan=2| at 3000 rpm

|1966–74 || MG Midget MkIII

|1967–68 || MG 1300/Wolseley 1300 || rowspan=8| at 5250 rpm || rowspan=5| at 3000 rpm

|1967–68 || Riley Kestrel 1300

|1967–68 || Vanden Plas Princess 1300

|1967–73 || Morris 1300

|1967–74 || Austin 1300

|1967 || MG 1275/Riley 1275 || rowspan=3| at 3500 rpm

|1967 || Wolseley 1275

|1967 || Vanden Plas Princess 1275

|1968–69 || Riley Kestrel 1300/Riley 1300 || at 6000 rpm || at 3000 rpm

|1968–71 || Austin America (automatic) || at 5250 rpm || at 2500 rpm

|1968–73 || Wolseley 1300 (manual) || at 5750 rpm || at 3000 rpm

|1968–73 || MG 1300 MkII || at 6000 rpm || at 3000 rpm

|1968–74 || Vanden Plas Princess 1300 (manual) || rowspan=2| at 5750 rpm || rowspan=2| at 3000 rpm

|1968 || MG 1300/Riley Kestrel 1300

|1969–71 || Morris 1300GT || at 6000 rpm || at 3250 rpm

|1971–82 || Mini Moke Californian Australian only.||||

|1969–74 || Mini 1275GT || at 5300 rpm || at 2550 rpm

|1969–74 || Austin 1300GT || at 6000 rpm || at 3250 rpm

|1971–80 || Morris Marina || at 5250 rpm || at 2500 rpm

|1971 || Austin Sprite || at 6000 rpm || at 3000 rpm

|1973–80 || Austin Allegro || at 5300 rpm || at 3000 rpm

|1974–80 || Mini 1275GT || at 5300 rpm || at 2550 rpm

A-Plus versions

British Leyland was keen to update the old A-series design in the 1970s. However, attempts at replacement, including an aborted early-70s British Leyland 'K engine' (unrelated to the later Rover K series) and an OHC version of the A series, ended in failure. During the development of what was to become the Austin Metro, engineers tested the A series against its more modern rivals and found that it still offered competitive (or even class-leading) 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 (from ). 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 engine 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 to 1992.

Applications:

{| class="wikitable"

! Years !! Model !! Power output !! Torque

| 1980–82 || Mini 1000/City/HL || at 4750 rpm || at 2000 rpm

| 1980–82 || Austin Allegro || at 5250 rpm || at 3000 rpm

| 1980–90 || Austin Metro || at 5400 rpm || at 2700 rpm

| 1982–88 || Mini HLE/City E/Mayfair || at 5000 rpm || at 2500 rpm

| 1981–86 || Austin Metro HLE || ||

| 1988–92 || Mini City/Mayfair || at 5250 rpm || at 2600 rpm

1275 Plus

The larger engine was also given the "A-Plus" treatment. This lasted from 1980 to 2000, making it the last of the A-series line.

{| class="wikitable"

|+Applications

! Years !! Model !! Power output !! Torque

| 1980–82 || Austin Allegro || at 5600 rpm || at 3200 rpm

| 1980–84 || Morris Ital || at 5300 rpm || at 2950 rpm

| 1980–90 || Austin Metro || at 5650 rpm || at 3100 rpm

| 1982–89 || MG Metro || at 6000 rpm || at 4000 rpm

| 1983–85 || Austin Maestro HLE || at 5500 rpm || at 3500 rpm

| 1983–93 || Austin Maestro || at 5800 rpm || at 3500 rpm

| 1984–89 || Austin Montego || at 5600 rpm || at 3500 rpm

| 1989–90 || Austin Metro GTa || at 6000 rpm || at 4000 rpm

| 1990–91 || Mini Cooper || at 5500 rpm || at 3900 rpm

| 1990–91 || Mini Cooper S || at 6000 rpm || at 3250 rpm

| 1991–96 || Mini Cooper 1.3i/Cabriolet || at 5700 rpm || at 3900 rpm

| 1991–96 || Mini Cooper S 1.3i || at 5800 rpm || at 3000 rpm

| 1992–96 || Mini 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 rpmthis 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 to 1990.

Applications:

1983–89 MG Metro Turbo, at 6130 rpm and at 2650 rpm
1989–90 Mini ERA Turbo, at 6130 rpm and at 3600 rpm

1275 MPi

Japanese Mini Paul Smith engine, notice the side radiator|thumb|right

MPi A-Series|thumb|right

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 to 2000. Few changes were made to ensure the engine complies with Euro 2 (later Euro 3) 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.

Applications

1997–2000 Rover Mini MPi 1.3i (TPi), at 5500 rpm and at 3000 rpm

JOHN COOPER GARAGES

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.

S pack (carb)
1st Si pack (Spi)
2nd Si pack (Spi)
3rd Si pack (Spi)
1997 Si pack (Mpi) @ 5500rpm
1999 Si pack (Mpi) @ 6000rpm

!Displacement

!Bore

!Stroke

!Horsepower

OHC version

With the intention of updating the current engine, for use in the new Mini Clubman (ADO20), 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 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.

{| class="wikitable"

|+OHC A-Series In May 1957, the engine was tested in one Austin A35, alongside a 20 hp, 500cc air-cooled, and later 670cc water-cooled, two-cylinder two-stroke engine developed by Dr Joe Ehrlich of EMC Motorcycles that was tested in one Austin A30 before being used in an experimental Austin-A30–based prototype with weight reduced to 584 kg (by way of a special lightweight body in steel that was lighter than normal, with altered panels to keep weight at a minimum) known as the Austin A20 or the "Lightweight Austin 7".

In 2021 retired racing driver and Bugatti specialist Ivan Dutton rebuilt an example of the four-stroke engine from an original head and cylinder block and documented the work on Youtube. He also has the EMC two-cylinder two-stroke engine which he plans to return to running condition.

Current use

This engine continues to be improved. It has a very large and wide market, whether in the classic car industry or the racing industry. It has 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 eight-valve and sixteen-valve versions, made in aluminium with five, seven or eight ports. Additionally over the past few decades it has not been unusual to see the A-Series stretched beyond 1275cc with capacities ranging from as low as 1293cc up to 1479cc, although it is commonly enlarged to 1380cc while retaining its reliability so long it is serviced regularly and well looked after.

The A-series engine is currently used in David Brown Mini Remastered. The engine is totally rebuilt, with new internals to an improved specification. The engine used is based in 1275cc MPi version, with larger capacity versions including the 1330cc Monte Carlo as well as the 1380cc and 1450cc Oselli Edition.

{| class="wikitable"

|+Mini Remastered updated version

!Displacement

!Bore

!Stroke

!Compression<br>ratio

!Carburation

!Horsepower

!@rpm

!Torque

!@rpm

|10.1:1

|MPi

|4600

|3100

|10.1:1

|MPi

| -

BMC A-series engine

Engine family list

A versions

803

948

848

997

998

1098

1070

970

1275

A-Plus versions

998 Plus

1275 Plus

1275 Turbo

1275 MPi

OHC version

Current use

Gallery

See also

Notes

References

Further reading

External links