BMC A-Series engine

BMC A-Series
Overview
Manufacturer Austin Motor Company
British Motor Corporation
British Leyland Motor Corporation
Rover Group
MG Rover Group
Production 1951–2000
Combustion chamber
Configuration Straight-4
Displacement 803 cc (49.0 cu in) to 1,275 cc (77.8 cu in)
Cylinder block alloy cast iron
Cylinder head alloy cast iron
Valvetrain OHV
Combustion
Fuel system Carburetor or Rover MEMS
Fuel type petrol
Cooling system water-cooled
Output
Power output 28 hp (21 kW; 28 PS) to 94 hp (70 kW; 95 PS)
Torque output 40 lb·ft (54 N·m) to 85 lb·ft (115 N·m)
Chronology
Successor Rover K-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.

The A-Series design was licensed by Nissan of Japan, along with other Austin designs. Improvements were rapid. Early change was to a fit 5 main bearing crank. Head was modified for first 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 170bhp CA18DET. All these engines show their lineage by the characteristic un-skirted crankcase block of the BMC A series, the A and E also having the bulge in the sump joint face for the oil pump drive. (Nissan engines with deep crankcase skirts are derived from the Mercedes OHC inline 6 that Nissan also licensed in the 1950's.)

Specifications

BMC A-Series engines
DisplacementBoreStrokeCompression
ratio		CarburationHorsepower@rpmTorque@rpm
803 cc 58 mm76.2 mm7.5:1one SU H2 sidedraft 30 PS (22 kW; 30 hp)5000 46 lb·ft (62 N·m) 2700
848 cc 62.9 mm68.26 mm8.3:1one SU HS2 sidedraft 33 PS (24 kW; 33 hp)5500 44 lb·ft (60 N·m) 2900
948 cc 62.9 mm76.2 mm—one SU HS2 sidedraft 37 PS (27 kW; 36 hp)4750 50 lb·ft (68 N·m) 2500
970 cc 70.6 mm61.91 mm—two SU HS2 sidedraft 65 PS (48 kW; 64 hp)6500 55 lb·ft (75 N·m) 3500
997 cc 62.43 mm81.28 mm—two SU HS2 sidedraft 55 PS (40 kW; 54 hp)6000 54 lb·ft (73 N·m) 3600
998 cc 64.58 mm76.2 mm8.3:1one SU HS2 sidedraft 39 PS (29 kW; 38 hp)4750 52 lb·ft (71 N·m) 2700
1071 cc 70.6 mm68.26 mm8.5:1two SU HS2 sidedraft 70 PS (51 kW; 69 hp)6000 62 lb·ft (84 N·m) 4500
1098 cc 64.58 mm83.72 mm8.5:1one SU HS2 sidedraft 47 PS (35 kW; 46 hp)5200 60 lb·ft (81 N·m) 2450
1275 cc 70.6 mm81.28 mm8.8:1one SU HS4 sidedraft 57 PS (42 kW; 56 hp)5300 69 lb·ft (94 N·m) 3000

All engines had a cast iron head and block, and two valves per cylinder in an OHV configuration. 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.[1] This does not include overseas production models such as Australian manufacture.

A versions

803

The original A-Series engine displaced just 803 cc and was used in the A30 and Morris Minor. It had an undersquare 58 mm (2.3 in) bore and 76.2 mm (3.00 in) stroke. This engine was produced from 1952–56.

Applications:

948

1956 saw a displacement increase, to 948 cc. 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.

Applications:

A diesel version of the 948 cc 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.

848

An 848 cc A-Series engine in a 1963 Austin Mini

The 62.9 mm (2.48 in) bore was retained for 1959s 848 cc 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.

Applications:

997

The one-off 997 cc version for the Mini Cooper used a smaller 62.43 mm (2.458 in) bore and longer 81.28 mm (3.200 in) stroke. It was produced from 1961–1964.

Applications:

998

The Mini also got a 998 cc 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.

Applications:

1098

The 1.1 L (1098 cc) version was produced for the larger BMC saloons. It was a stroked (to 83.72 mm (3.296 in)) version of the 998 previously used in the Riley Elf and Wolseley Hornet. It was produced from 1962–80.

Applications:

1071

The 1071 cc 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 68.26 mm (2.687 in) stroke from the 848. It was only produced in 1963–1964. Paired with the even rarer 970 cc version, below, it became that rarest of things: an oversquare A-series engine.

Applications:

970

The Mini Cooper S next moved on to a 970 cc version. It had the same 70.6 mm (2.78 in) bore as the 1071 cc Cooper S but used a shorter 61.91 mm (2.437 in) stroke. It was produced from 1964–1965.

Applications:

1275

The largest A-Series engine displaced 1.3 L (1275 cc). It used the 70.6 mm (2.78 in) bore from the Mini Cooper S versions but the 81.28 mm (3.200 in) stroke from the plain Mini Cooper. It was produced from 1964 until 1980, when it was replaced by an A-Plus version.

Applications:

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 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' 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 998cc and 1275cc, 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). 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 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 and red for 1275 cc engines.

To allow the MG Metro to compete with larger, more powerful hot hatchbacks a turbocharged version of the 1275cc 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 4000rpm - 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 1275cc A-Plus Turbo was 94 horsepower 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 horsepower.

998 Plus

The A-Plus version of the 998 cc motor was produced from 1980–92.

Applications:

1275 Plus

The big 1.3 L (1275 cc) engine was also given the "A-Plus" treatment. This lasted from 1980–2000, making it the last of the A-Series line.

Applications:

1275 Turbo

Turbo versions lasted from 1983–90.

Applications:

1275 MPi

Japanese Mini Paul Smith engine, notice the side radiator

A special "twin-port injection" version of the 1.3 L (1275 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.

Applications

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[2]

See also

Wikimedia Commons has media related to BMC A engine.

References

  1. ↑ Austin Morris (BL) internal documents archives.
  2. ↑ "Engines: A-series". Aronline.co.uk. Archived from the original on 23 November 2010. Retrieved 2010-12-01.

Northey, Tom, editor in chief. World of Automobiles (London: Orbis Publishing, 1974), Volume 9, p. 1054, "Mini", and Volume 2, p. 121, "Austin Allegro."

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