The 10/30, 11/40 and 12/40 cars, of which very few survive, have side-valve engines, of 1460cc for the 10/30 and 1598cc for the 11/40 and 12/40. The earliest 10/30s were advertised in July 1920 as ‘The Car for the Connoisseur’ and were priced at £685 for the open two-seater, relatively expensive at that time for a 'Ten'. Within a year, private owners and works drivers were winning numerous sporting awards all over the country, and this set a trend which was to continue throughout the 1920s and beyond. The early emphasis on quality and performance set the tone for all subsequent models.
12/50s, first advertised in late 1923, and 12/60s have overhead valves. The crankcase and sump are aluminium castings with cast iron being used for the cylinder block and head. The camshaft, dynamo and magneto are driven by a train of gears from the front of the engine. Later cars feature electric fuel pumps and coil ignition. There is no water pump.
Sports 12/50s were fitted with a short-stroke big-port engine of 1496 cc (68x103 mm) enabling them to compete in 1500 cc events. Touring 12/50s generally had a long-stroke small-port engine of 1645 cc (69x110 mm). Apart from the difference in stroke, bore and the detail design of the cylinder head, the two engines are practically identical, with many parts being interchangeable. Production of the 12/50 ceased for a short time between 1929 and 1930, but it was reintroduced with several chassis improvements as the TJ 12/50 to meet the deepening economic crisis. It retained the familiar 12/50 mechanical components, and a twin SU carburettor sports version, named the 12/60, was introduced early in 1931.