The BL O-series engine is a straight-4 automobile engine family that was produced by the Austin-Morris division of British Leyland (BL) as a development of the BMC B-series engine family.
BL O-series engine
The BMC B series was a line of straight-4 & straight-6 internal combustion engine mostly used in motor cars, created by British automotive manufacturer Austin Motor Company.
BMC B-series engine
A sectioned illustration of the Austin A40's 1200cc engine – the direct predecessor to the B series
B-series 1500 engine in a Nash Metropolitan Series 3