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BMC B-Series engine

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Title: BMC B-Series engine  
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Subject: Morris Cowley, Morris Commercial J2, Morris Major, Hindustan Ambassador, Austin Freeway
Collection: Bmc Engines, British Leyland Engines, Gasoline Engines by Model
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BMC B-Series engine

Manufacturer BMC
Production 1954–1980
Combustion chamber
Configuration I4 and I6
  • 1.2 L, 1.5 L, 1.6 L, 1.8 L (I4)
  • 2.4 L (I6)
Cylinder bore 65.5–80.26 mm (2.6–3.2 in)
Piston stroke 89 mm (3.5 in)
Cylinder block alloy Cast iron
Cylinder head alloy
  • Cast iron
  • Aluminum (Twin-Cam)
  • OHV
  • DOHC (Twin-Cam)
Fuel system Carburetor
Fuel type Gasoline & diesel versions
Cooling system Water-cooled

The BMC B-series was a straight-4 internal combustion engine family, mostly used in motor cars, created by British company Austin Motor Company.


  • Design 1
  • Engine types 2
    • 1.2 litre engines 2.1
    • 1.5 litre engines 2.2
    • Twin-Cam engines 2.3
    • 1.6 litre engines 2.4
    • 1.6 litre Mark II engines 2.5
    • 1.8 litre engines 2.6
    • 2.4 litre engines 2.7
  • Engine numbering 3
    • Early numbering system 3.1
    • 1957–70 numbering system 3.2
    • 1970 onwards numbering system 3.3
  • See also 4
  • References 5
  • External links 6


The precursor of the "B" series engine was a 1200 cc OHV engine which was used in the 1947 Austin A40 Devon. This A40 Devon engine was based on a pre-war Side-valve design. Austin realised that eventually they would need an engine that could power many of its forthcoming medium-sized cars, and this would require an engine of at least 1500 cc capacity. Since the A40 Devon engine could not have its capacity enlarged, a new engine was designed, which, although superficially similar, was longer and heavier than the A40 Devon engine. The design of this new engine commenced around January 1952, and was designated as the "B" series. Displacements ranged widely from 1.2 L to 2.4 L, the latter being an Australia only production six-cylinder variant. 1.5 L and 1.8 L displacements were most common. Petrol versions were produced in the greatest numbers, but diesel versions exist for both cars and marine applications.

The engine was of conventional construction with a one-piece crankcase and cylinder block in cast iron with the crankcase extending down to the lowest level of the main bearing caps, and with cylinder head also usually in cast iron. The sump was made from pressed steel. Early engines used a three-bearing crankshaft, but later engines used five bearings. On all except the rare twin overhead camshaft variant, the camshaft — which was chain driven and mounted low in the block — operated the overhead valves via pushrods and rocker arms. The two inlet ports in the non-crossflow cylinder head were shared between cylinders 1 + 2 and 3 + 4 and the three exhaust ports between cylinder 1, 2 + 3 and 4. Valve clearance was adjustable by screws and locknuts on the rocker arms. The B-Series shares many design features (such as the heart-shaped combustion chambers and siamese inlet ports designed by Harry Weslake), as well as its basic layout and general appearance, with the smaller A-Series engine, but differed by having a full-depth skirt to the block. This provided excellent bottom-end strength which made the engine highly durable and suitable for developing into diesel versions in later years.

Engine types

1.2 litre engines

The 1.2L (1199.6 cc) version was the first version of the engine. The bore was 65.5 mm (2.58 in) and the stroke 89 mm (3.5 in). The maximum power output was 39 bhp (29 kW) at 4300 rpm.

After the formation of British Motor Corporation (BMC) it was used in the following vehicles:

1.5 litre engines

B-Series 1500 engine in a Nash Metropolitan Series 3

The 1.5 L (1489 cc) version was first used in 1953 in the MG Magnette ZA in twin carburettor version and in 1954 in the Morris Oxford series II and Austin Cambridge. In 1957, it was used in the original MGA. Output in twin carburettor form was 68–72 bhp (51–54 kW) and 55 bhp (41 kW) with a single carburettor. Bore was 73.03 mm (2.875 in) and stroke was 89 mm (3.5 in).

There was also a diesel version of this engine size. Power output was 40 bhp (30 kW) at 4,000 rpm and torque 64 lbf·ft at 1,900 rpm.


Twin-Cam engines

A special Twin-Cam (DOHC) version of the 1588 cc B-series engine was produced for the MGA. Output was 108 bhp (81 kW) at 6700 rpm in the high-compression (9.9:1) version and 100 bhp (75 kW) in the optional low-compression (8.3:1) version. The engine block was cast iron, but the crossflow eight-port cylinder head was of aluminium alloy. Drive to the twin camshafts was by chain from a gear-driven, half-speed shaft running in the space that would have been occupied by the conventional camshaft. This engine gained a reputation for being unreliable in service, especially in the high-compression version which needed high-octane fuel, but this has now been largely overcome. The piston burning habits — thought to be the result of ignition timing — was later discovered to be due to a vibration induced lean burn situation involving the float bowls, easily correctable by flexibly mounting the carburettors.

A total of 2,111 cars were built, in both coupé and roadster versions.

A very few engines with the special displacement of 1762 cc were produced for racing purposes.


1.6 litre engines

The engine was enlarged to 1.6 L (1588 cc) in 1958 by increasing the bore to 75.4 mm (2.97 in).


1.6 litre Mark II engines

The engine was enlarged to 1622 cc in 1961 with another bore increase, this time to 76.2 mm (3.00 in).


The 1622cc B-Series also formed the basis of the "Blue Streak" engine developed by BMC Australia for use in the locally-built Austin Freeway and Wolseley 24/80 models, both in turn variants of the existing Austin A60 Cambridge. The "Blue Streak" was an inline-6 development of the B-Series, adding two extra cylinders to create a 2433cc engine. Different market demands in Australia required the fitting of a six-cylinder engine to a car the size of BMC's mid-range Farina model and the corporate C-Series engien would not fit, requiring the development of the unique "Blue Streak" engine. Both models were withdrawn in 1965 and no further use of the engine was made.

1.8 litre engines

The engine was enlarged again to 1.8 L (1798 cc) in 1962. Bore was 80.26 mm (3.160 in) and stroke was still 89 mm (3.5 in). The engine at first had a three-bearing crankshaft with a five-bearing version appearing in 1964.

There was also a diesel version of this capacity, used in the Leyland Sherpa van, and built under license in Turkey for many years. It is still widely used on narrowboats on the canals of the UK.


2.4 litre engines

There was a 2433 cc six-cylinder unit, named "Blue Streak", which was used in the Australian Austin Freeway and Wolseley 24/80.

Engine numbering

There were two series of engine numbers used; BMC changed the system at the end of 1956.

Early numbering system

Numbers were of the style "BP15GB" followed by a serial number, where:

  • B = B series engine
  • P = Pushrod
  • 15 = capacity
  • G = MG (for full list see Later numbering system below)
  • The final letter is the version of the engine.

1957–70 numbering system

Numbers were of the style "15GB-U-H" plus a serial number, where:

  • 15 = capacity
  • G = MG (other letters were: A = Austin, B = Industrial, H = Miscellaneous, J = Commercial, M = Morris, R = Riley, V = Vanden Plas and W = Wolseley )
  • B = B series engine
  • U = Central gear change (other letters were: A = Automatic, M = Manumatic clutch, N = Column change, O = Overdrive and P = Police)
  • H = High compression (alternatively L = Low compression)

1970 onwards numbering system

Numbers were simplified to "18 V" plus a serial number, where 18 represents the capacity and V = vertical, i.e. longitudinal (in-line, not vee-arranged) engine with rear-wheel drive, and H = Horizontal, i.e. transverse engine with front-wheel drive.

There was sometimes a country indicator after the first part of the code, e.g. "18V-Z" was use for some United States (except California) MG MGB engines.

See also


External links

  • Full list of engine codes
  • B series engine description at "the unofficial Austin Rover resource"
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