Austin Seven four-stroke engine, 1928.
© Science Museum / Science & Society Picture Library
This side view of the engine shows its four cylinders, each containing a piston. The piston moves up and down 2,400 times a minute; a proces that can be described in four movements or strokes. First, the piston moves down, and petrol vapour is forced into the cylinder. The piston then returns to compres the vapour towards the top of the cylinder. Then, as the spark plug ignites the vapour, the piston is sent down the cylinder. Lastly, the piston returns up the cylinder, moving the fumes to the exhaust pipe. Designed by Sir Herbert Austin (1866-1941), the Austin Seven first appeared in 1922, and in th 1920s and 1930s became the first British-built car to enjoy mas appeal. By 1938, over 300,000 had been built in England alone.