The air-cooled, side valve, engine was a horizontally opposed twin and was originally of 998 cc capacity, with a bore of 85 mm and a stroke of 88 mm, but this was increased to 1134 cc with a 100 mm stroke in 1923. This did not affect the RAC hp rating, which remained 8 hp. The original engine had a peak output of at 2600 rpm. Although there was a conventional looking radiator it was a dummy. Cooling was supplied through air scoops on the side of the bonnet and it was rumoured that after hard driving at night the cylinder heads could be seen glowing red through them. Two cross-members of the frame supported at three points the assembled unit of engine and clutch and a three speed gearbox with reverse. The rear wheels were driven through a fabric joint and propellor shaft to a universal joint and an under-worm wheel type rear axle. A dynamo was belt driven from the propeller shaft. An electric starter was optional from 1923. A six volt lighting set was provided.