Created in 1951 by the Austin Motor company, this engine (and all its variants) is the most produced engine in history (Rover stopped making it in 2000).
Originally designed in as an 803cc (yes, 0.8l) for the A30 and Morris Minor, it has been fitted to countless BL vehicles, and was even licensed to Nissan and became the basis for many of their engines.
BL improved the design in the 70's with the A+ series. More power, uprated components.
It still however remained the simplest engine to work on. It's the one I learned to work on.
I had a 998cc Austin Mini City made in 1984 as my first car, brought as a present from my Sister. Affectionately named by my then university mates as the BunterMobile.
With the miles I was putting in it from here to Manchester, something was bound to give, and it did.
Every 200 miles or so, the head gasket would blow for no reason (always on my way home). The first time my Dad and I stripped it down and replaced it, it took us the best part of two days (with the workshop manual). At the end it used to take me on my own an hour dead.
Turned out that some smart-arse had fitted it with an A+ series head. Something you can do, but there is no breather pipe to it from the block, and to make it fit right, it needs to be skimmed. Whenever we took the head off to change the gasket, it always went in the same place - between the two centre cylinders.
Eventually, we sussed out that this same smart-arse had skimmed too much off the head, and the centre valves were hitting the block and lifting it, causing the gasket to go (the biggest clues was the two feint imprints of where the valve had hit the block).
My 998cc Mini, and the 1098cc Austin 1100, had given me the foundation to know how to repair and tinker with engines.