BL O-Series engine

The BL O-Series engine was a straight-4 automobile engine family produced by British Leyland (BL) as a development of the BMC B-Series engine family.

Introduced by BL in 1978 in the rear wheel drive Series 2 Morris Marina and the smaller engined versions of the front wheel drive Leyland Princess, it was intended to replace the 1.8 litre 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 litres as well as 2.0 litres, it proved to be reliable and was widely used in BL vehicles. These included the rear wheel drive Morris Ital of 1980 (1.7 litres or 2.0 litres with an automatic gear box), the rear wheel drive Rover SD1 of 1982 (2.0 litre only), and 1.7 and 2.0 litres 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 litre 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 Leland front wheel drive products. The 1.7 litre O-Series was not used in these vehicles, which featured R- and later S-Series 1.6 litre units.

In 1986, BL collaborated with Perkins to convert the O-series to run on diesel. The oil-burning versions (known as the "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.

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 litre unit was known as the M-Series, and was further reworked into the T-Series in 1992. The original 8-valve version of the O-Series was also briefly used in budget versions of the Rover 800.

Automobiles using the O-Series

Examples of cars using a version of the O-Series engine:

• Austin Maestro 2.0 L, 2.0 L Diesel
• Austin Montego 2.0 L, 2.0 L Diesel
• Princess / Austin Ambassador 1.7 L, 2.0 L
• Morris Ital 1.7 L, 2.0 L automatic
• Morris Marina 1.7 L
• Rover 800 2.0 L
• Rover SD1 2.0 L