Expert advice

01 Engine

A pressed up crank assembly was supported in the vertically-split crankcase/gearbox casting shells with two ball journal bearings on the right (drive) side and one on the left. The conrod was held between full circle flywheels giving the standard 58mm Bantam stroke. There was a roller big-end and needle roller small-end. The piston moved in a four-port cast-iron barrel, 61.5mm bore for 173cc. Cylinder head was aluminium. Later heads had a central spark plug. Engine lubrication is up to 32:1 pre-mix with the main bearings dependent on transmission oil. Carburettor was