| BL O-series | |
| Manufacturer: | British Leyland Motor Corporation Austin Rover Group |
| Production: | 1978–1993 |
| Configuration: | Straight-4 |
| Block: | cast iron |
| Head: | aluminium |
| Valvetrain: | SOHC |
| Fuelsystem: | Carburettor or Fuel Injection |
| Fueltype: | petrol |
| Coolingsystem: | water-cooled |
| Aka: | Rover M8 |
The BL O-series engine is an automobile straight-four engine family that was produced by the Austin-Morris division of British Leyland (BL) as a development of the BMC B-series engine family. (See also another B-series successor, the BMC E-series engine.)
Introduced by BL in 1978 in the rear wheel drive Series 3 Morris Marina and the smaller engined versions of the front-wheel-drive Princess, it was intended to replace the 1.8 L B-series unit. The main advance over the B series was that the new unit was of belt driven overhead camshaft configuration, with an aluminium cylinder head.
Offered in the unusual capacity of 1.7 L as well as 2.0 L, it proved to be reliable and was widely used in BL vehicles. These included the rear wheel drive Morris Ital of 1980 (1.7 L or 2.0 L with an automatic gear box), the rear wheel drive Rover SD1 of 1982 (2.0 L only), and 1.7 L and 2.0 L in the front wheel drive Austin Ambassador – in fact the only engine offered in this model. In 1984, it was reworked for installation in high specification 2.0 L versions of the front-wheel drive Austin Maestro and Austin Montego, where it was later optionally available with fuel injection or turbo-charging. This installation of the O-series was adapted for use with the Honda PG-1 end-on manual gearbox, replacing the gearbox-in-sump design traditionally used on British Leyland front-wheel-drive products. The 1.7 L O-series was not used in these vehicles, which featured R- and later S-series 1.6 L units instead. The cylinder blocks of the transmission-in-sump (Princess/Ambassador), rear wheel drive longitudinal (Marina/Ital/Rover SD1), and the transverse, end-on transmission (Maestro/Montego/Rover 800) versions are not interchangeable.
A notable advantage of the 2-litre, petrol O-series engine is that the cylinder head does not require modification to run on unleaded petrol due to having hardened valve seats. Other O-series engines, however, cannot run on unleaded without modification of the cylinder head or use of an additive.
By 1987, British Leyland (now known as the Rover Group) equipped the O-series with a 16-valve cylinder head for the Rover 800. This 2.0 L unit was known as the M series, and was further reworked into the T series in 1992. The 8-valve version of the O-series was also briefly used in budget versions of the Rover 800, although confusingly this was given the "M8" designation in official Rover service publications – implying it was an 8-valve version of the M Series engine, although it was identical to the O series used in the Maestro and Montego.
The 1.7 L displaces . It is an 8-valve SOHC design with an aluminium head and iron block. The engine is a spark-ignition 4-stroke naturally aspirated petrol engine. Fuel system is via carburettor. Power is at 5150 rpm in the Morris Marina, and at 5200 rpm in the Austin Ambassador. Net torque is at 3500 rpm.[1] When installed in the Sherpa van, it had a lowered compression ratio of 7.8 : 1 and could be run on lower octane, "two-star" petrol. Maximum power for this variant is at 4100 rpm, torque is at 3000 rpm.[2]
Bore x stroke: NaNmm
The 2.0 L displaces . It is an 8-valve SOHC design with an aluminium head and iron block. The engine is a spark-ignition, four-stroke naturally aspirated petrol engine. Fuel system is via carburettor. Power is at 5250 rpm in the Austin Ambassador. Net torque is at 3250 rpm.[4] Maximum power for the lower compression variantinstalled in the Freight Rover (later Leyland DAF 200/400) is at 4250 rpm, torque is at 3500 rpm.
Bore x stroke: NaNmm
In 1986, BL collaborated with Perkins to convert the O-series to run on diesel. The oil-burning versions, known as the Rover MDi or Perkins Prima, proved to be highly successful in the Maestro and Montego, and helped sustain the ailing mid-sized models into the 1990s. Perkins successfully marketed the engine under its own brand in the industrial and marine sectors. It was further developed by MG Rover to form their Rover L-series engine, which was manufactured until 2005.
Examples of vehicles using the diesel version of the O-series engine: