- Main article: Leyland for the Main company details.
The Leyland Company built a range of Engines to power their own vehicles and sell to other vehicle builders. The engines were often built with different versions to suit applications in the tractors, Trucks, Busses and static applications such as generators and pumps etc.
As the Leyland company grew from the various company take overs and mergers a diverse range of products and production facilities were consolidated an strategy of vertical integration and using inhouse production lead to the consolidation of engine production. Leyland being used here to refer to the Leyland company, BMC, British Leyland, Marshall etc. The firm also used the Leyland engines in some Aveling Barford products when they owned the company. They also took over Albion Motor and AEC
- Leyland build there first diesel engine in 1933.
- Post war 7.4 litre Leyland engines fitted in pre-war buses to upgrade them.
- When they took over BMC in 1968 they inherited the Bathgate Tractor and Truck plant which built the 4 cylinder 3.77 litre used in the 4/65 tractor. This was redesigned and appeared as the 4/98 model in 1972.
- The 2.8 litre 3-cylinder from the 3/45 tractor, built in Birmingham, was discontinued in 1969, where the new 344 model tractor used the 3.4TD engine.
- From 1950 and until around 1972, 5.1 ltr and 5.7 ltr 6-cylinder diesel engines was built, they was redesigned as the 6/98 model.
- Leyland 0.600 Engine a 9.8 litre also fitted to Routemaster buses.
- Leyland 680 Engine.this was a 150 hp horizontal engine used in buses and DMU units.
- Leyland 4/98 DT, NT, TT fitted in 255, 262, 462, 270, 272, 282, 602, 604, 702, 704, 802, 804
- Leyland 6/98 285, 2100