BMC A-series engine
Austin Motor Company'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 (Jaguar) 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 (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.
|BMC A series|
|Manufacturer||Austin Motor Company|
British Motor Corporation
British Leyland Motor Corporation
MG Rover Group
|Displacement||803–1,275 cc (49.0–77.8 cu in)|
|Block material||Cast iron|
|Head material||Cast iron|
|Valvetrain||OHV 2 valves x cyl.|
|Compression ratio||7.5:1, 8.3:1, 8.5:1, 8.8:1, 9.4:1, 10.5:1|
|Turbocharger||Garrett T3 (1275 Turbo only)|
|Fuel system||SU carburettor or fuel injection|
|Power output||28 to 94 bhp (21 to 70 kW; 28 to 95 PS)|
|Torque output||40 to 85 lb⋅ft (54 to 115 N⋅m)|
|Successor||Rover K-series engine|
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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 170 bhp (127 kW) 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.
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.
|803 cc (49.0 cu in)||57.92 mm (2.280 in)||76.2 mm (3.00 in)||7.5:1||Single H2||30 PS (22 kW; 30 hp)||5000||46 lb⋅ft (62 N⋅m)||2700|
|848 cc (51.7 cu in)||62.9 mm (2.48 in)||68.26 mm (2.687 in)||8.3:1||33 PS (24 kW; 33 hp)||5500||44 lb⋅ft (60 N⋅m)||2900|
|947 cc (57.8 cu in)||76.2 mm (3.00 in)||—||37 PS (27 kW; 36 hp)||4750||50 lb⋅ft (68 N⋅m)||2500|
|970 cc (59 cu in)||70.6 mm (2.78 in)||61.95 mm (2.439 in)||Twin HS2||65 PS (48 kW; 64 hp)||6500||55 lb⋅ft (75 N⋅m)||3500|
|997 cc (60.8 cu in)||62.43 mm (2.458 in)||81.4 mm (3.20 in)||55 PS (40 kW; 54 hp)||6000||54 lb⋅ft (73 N⋅m)||3600|
|998 cc (60.9 cu in)||64.58 mm (2.543 in)||76.2 mm (3.00 in)||8.3:1||Single HS2||39 PS (29 kW; 38 hp)||4750||52 lb⋅ft (71 N⋅m)||2700|
|1,071 cc (65.4 cu in)||70.6 mm (2.78 in)||68.4 mm (2.69 in)||8.5:1||Twin HS2||70 PS (51 kW; 69 hp)||6000||62 lb⋅ft (84 N⋅m)||4500|
|1,098 cc (67.0 cu in)||64.58 mm (2.543 in)||83.8 mm (3.30 in)||Single HS2||47 PS (35 kW; 46 hp)||5200||60 lb⋅ft (81 N⋅m)||2450|
|1,275 cc (77.8 cu in)||70.6 mm (2.78 in)||81.4 mm (3.20 in)||8.8:1||Single HS4||57 PS (42 kW; 56 hp)||5300||69 lb⋅ft (94 N⋅m)||3000|
The original A-series engine displaced just 803 cc (49.0 cu in) and was used in the A30 and Morris Minor. It had an undersquare 57.92 mm × 76.2 mm (2.280 in × 3.000 in) bore and stroke. This engine was produced from 1952–56.
- 1952–56 Austin A30, 28 hp (21 kW) at 4400 rpm and 40 lb⋅ft (54 N⋅m) at 2200 rpm
- 1952–56 Morris Minor Series II, 30 hp (22 kW) at 4800 rpm and 40 lb⋅ft (54 N⋅m) at 2400 rpm
1956 saw a displacement increase, to 947 cc (57.8 cu in). This was accomplished by increasing the bore to 62.9 mm (2.48 in) while retaining the original 76.2 mm (3.00 in) stroke. It was produced until 1964.
A diesel version of the 947 cc (57.8 cu in) A-series engine (producing 16 hp (12 kW) at 2,500 rpm and 38 lb⋅ft (52 N⋅m) torque at 1,750 rpm) was produced for the BMC Mini Tractor. It was developed with the help of Ricardo Consulting Engineers. 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. 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.
The 62.9 mm (2.48 in) bore was retained for 1959s 848 cc (51.7 cu in) Mini version. This displacement was reached by dropping the stroke to 68.26 mm (2.687 in). This engine was produced through to 1980 for the Mini, when the 998 A-Plus version supplanted it.
|1959–69||Austin Seven/Austin Mini/Morris Mini||34 hp (25 kW) at 5500 rpm||44 lb⋅ft (60 N⋅m) at 2900 rpm|
|1961–62||Riley Elf/Wolseley Hornet|
|1963–68||Austin A35 Van|
|1969–80||Mini 850/City||33 hp (25 kW) at 5300 rpm|
The one-off 997 cc (60.8 cu in) version for the Mini Cooper used a smaller 62.43 mm (2.458 in) bore and longer 81.4 mm (3.20 in) stroke. It was produced from 1961–1964.
- 1961–1964 Austin/Morris Mini Cooper, 55 hp (41 kW) at 6000 rpm and 54 lb⋅ft (73 N⋅m) at 3600 rpm
The Mini also got a 998 cc (60.9 cu in) version. This was similar to the 948 in that it had the same 76.2 mm (3.00 in) stroke but the bore was increased slightly to 64.58 mm (2.543 in). It was produced from 1962–92.
The 1.1 L; 67.0 cu in (1,098 cc) version was fitted to:
- MG Midget Mk1 1098cc from Oct 62- 64
- MG Midget Mk2 1098cc of 1964- 66
- Austin A35 Van 1098cc of 1962- 68
- Austin A40 Farina Mk2 - From Oct 62- 68
- Morris Minor from Oct 62- 71.
- Austin / Morris BMC Saloon from 1962.
- Mini and its derivatives, the 1098cc engine mounted transversely.
The 1,071 cc (65.4 cu in) version was another one-off, this time for the Mini Cooper S. It used a new 70.6 mm (2.78 in) bore size and the 68.4 mm (2.69 in) stroke from the 848. It was only produced in 1963–1964. Paired with the even rarer 970 cc (59 cu in) version, below, it became that rarest of things: an oversquare A-series engine.
- 1963–1964 Austin/Morris Mini Cooper S, 70 hp (52 kW) at 6000 rpm and 62 lb⋅ft (84 N⋅m) at 4500 rpm
The Mini Cooper S next moved on to a 970 cc (59 cu in) version. It had the same 70.6 mm (2.78 in) bore as the 1071 cc Cooper S but used a shorter 61.95 mm (2.439 in) stroke. It was produced from 1964–1965.
- 1964–1967 Austin/Morris Mini Cooper S, 65 hp (48 kW) at 6,500 rpm and 55 lb⋅ft (75 N⋅m) at 3,500 rpm
The largest A-series engine displaced 1.3 L; 77.8 cu in (1,275 cc). It used the 70.6 mm (2.78 in) bore from the Mini Cooper S versions but the 81.4 mm (3.20 in) 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.
|998 cc (60.9 cu in)||64.58 mm (2.543 in)||76.2 mm (3.00 in)||SU||44 PS (32 kW; 43 hp)||5250||52 lb⋅ft (71 N⋅m)||3000|
|1,275 cc (77.8 cu in)||70.6 mm (2.78 in)||81.4 mm (3.20 in)||SU or MEMS Single Point Injection||62 PS (46 kW; 61 hp)||5700||61 lb⋅ft (83 N⋅m)||3000|
|1,275 cc (77.8 cu in)||9.4:1||SU HIF44 carburettor with an automatic pressure-regulated fuel system||95 PS (70 kW; 94 hp)||6130||85 lb⋅ft (115 N⋅m)||3600|
|1,275 cc (77.8 cu in)||10.5:1||MEMS Multi Point Injection||64 PS (47 kW; 63 hp)||5500||70 lb⋅ft (95 N⋅m)||3000|
British Leyland 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 (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 998 and 1,275 cc (60.9 and 77.8 cu 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 6,000 to 12,000 miles (9,700 to 19,300 km)). 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 80,000 to 100,000 miles (130,000 to 160,000 km) 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 998 cc (60.9 cu in) and red for 1,275 cc (77.8 cu in) engines.
The A-Plus version of the 998 cc (60.9 cu in) motor was produced from 1980–92.
|1980–82||Mini 1000/City/HL||39 hp (29 kW) at 4750 rpm||52 lb⋅ft (71 N⋅m) at 2000 rpm|
|1980–82||Austin Allegro||44 hp (33 kW) at 5250 rpm||52 lb⋅ft (71 N⋅m) at 3000 rpm|
|1980–90||Austin Metro||41 hp (31 kW) at 5400 rpm||51 lb⋅ft (69 N⋅m) at 2700 rpm|
|1982–88||Mini HLE/City E/Mayfair||40 hp (30 kW) at 5000 rpm||50 lb⋅ft (68 N⋅m) at 2500 rpm|
|1981–86||Austin Metro HLE||46 bhp (34 kW)||52 lb⋅ft (71 N⋅m)|
|1988–92||Mini City/Mayfair||42 hp (31 kW) at 5250 rpm||58 lb⋅ft (79 N⋅m) at 2600 rpm|
The larger 1.3 L; 77.8 cu in (1,275 cc) engine was also given the "A-Plus" treatment. This lasted from 1980–2000, making it the last of the A-series line.
To allow the MG Metro to compete with larger, more powerful hot hatchbacks a turbocharged version of the 1,275 cc (77.8 cu in) 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 1,275 cc (77.8 cu in) A-Plus Turbo was 94 bhp (70 kW) 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 200 bhp (150 kW). Turbo versions lasted from 1983–90.
- 1983–89 MG Metro Turbo, 94 hp (70 kW) at 6130 rpm and 85 lb⋅ft (115 N⋅m) at 2650 rpm
- 1989–90 Mini ERA Turbo, 94 hp (70 kW) at 6130 rpm and 85 lb⋅ft (115 N⋅m) at 3600 rpm
A special "twin-port injection" version of the 1.3 L; 77.8 cu in (1,275 cc) engine was developed by Rover engineer, Mike Theaker. It was the last A-series variant, produced from 1997–2000. Japanese model received 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.
- 1997–2000 Rover Mini MPi 1.3i (TPi), 63 hp (47 kW) at 5500 rpm and 70 lb⋅ft (95 N⋅m) 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) 77 bhp (57 kW)
- 1st Si pack (Spi) 77 bhp (57 kW)
- 2nd Si pack (Spi) 82 bhp (61 kW)
- 3rd Si pack (Spi) 86 bhp (64 kW)
- 1997 Si pack (Tpi) 85 bhp (63 kW) @ 5500rpm
- 1999 Si pack (Tpi) 90 bhp (67 kW) @ 6000rpm
|Wikimedia Commons has media related to BMC A engine.|
Northey, Tom, editor in chief. World of Automobiles (London: Orbis Publishing, 1974), Volume 9, p. 1054, "Mini", and Volume 2, p. 121, "Austin Allegro."
- "A-series engine". The Unofficial Austin-Rover Web Resource. Archived from the original on 27 September 2007. Retrieved 13 April 2005.
- "Turbo Minis". The No.1 Turbocharged A-series resource. Archived from the original on 9 April 2005. Retrieved 13 April 2005.
- Robson, Graham (2011). The A-Series Engine: Its First Sixty Years. Haynes. ISBN 978-0-85733-083-3.