The cylinder head is not detachable and the cylinders are cast "en bloc". Each cylinder is served by two tulip shaped inlet and exhaust valves. Because they are small and lightly stressed they are able to function for a considerable mileage without attention. The single overhead camshaft runs in five phosphor bronze bearings, and the valves are operated by rockers, which are mounted on two parallel rods one on each side of the camshaft. The rocker arms are fitted with hardened steel rollers at the camshaft end, and at the opposite end there is a tappet screw secured by means of a lock nut. Each valve is fitted with two springs.

The crankshaft runs in five white metal bearings, and it prevented by moving sideways by a double thrust ball race. Aluminium pistons with four rings are fitted, and the camshaft drive is by means of spiral beval gears, and a vertical shaft driven from the front end of the crankshaft.

Each cylinder has two parking plugs and two magnetos are fitted, one to operate each set of plugs. The two magnetos are synchronised to spark simultaneously. The firing order is 1,3,4,2. and No. 1 cylinder is the one nearest the radiator. Water from the radiator is circulated by a vane pump, which is driven off the magneto cross-shaft and is situated immediately behind the radiator. The temperature of the water in the block is controlled by the thermostat when the engine is running. The thermostat is designed to open at 75 degrees centigrade. The starter motor is positioned on the nearside of the engine in the crankcase casting, and is held in position by a taper cotter pin. A shaft with a sliding splined joint at the front-end and a Hardy disc coupling at the rear-end connects the clutch to the gearbox. The shaft is hollow and is filled with oil via the nipple, which provides lubrication for the splined joint at the front.