ENGINE - 56x61 mm. (597 c.c.). Four cylinders cast " en bloc " in square formation.
Detachable cylinder head with integral radial induction manifold. Totally enclosed valves operated by overhead camshaft. The overhead camshaft and the magdyno are driven by automatically tensioned roller chains. 14 mm. sparking plugs. The twin crankshafts are mounted in large diameter ball bearings and are coupled by hardened and ground gears immersed in oil in a separate compartment within the crankcase. Roller bearing big-ends. Special aluminium alloy pistons.
LUBRICATION - By large single plunger pump. Approximately 4-gallon of oil is contained in the lower half of the crankcase, which has an accessible filler and dip-stick level indicator. A tecalemit oil filter, quickly detachable for cleaning, is arranged in the oil circuit.
CARBURETTER - Amal. Specially designed for " Square Four."
IGNITION SWITCH - Incorporated in the Instrument panel.
GEARBOX - Four-speed. Foot control.
TRANSMISSION - Engine shaft shock absorber. Polished aluminium oil bath chain case. Rear chain fully protected and automatically lubricated.
EXHAUST SY8TEM - Two-port interconnected.
WHEELS - Dunlop Tyres, 26x3.25. Chromium brake plates. Chromium rims. Black centres.
MUDGUARDS - Robust ribbed section steel guards, fully valanced, as illustrated. Tail of rear guard hinged to facilitate wheel removal.
PROP STAND - Fitted to the offside of the machine in addition to the two normal stands.
TANK - All-steel saddle type, with Instrument panel. 3J-gallon capacity. Superbly finished Chromium and Black, lined Gold.