Four-cylinder overhead valve unit, 3.21 in. (81.5 mm.) bore by 3.0 in. (7.62 mm.) stroke, has a capacity of 1,592 c.c. (97.1 cu. in.) and develops a gross b.h.p. of 54 at 4,400 r.p.m. and 80 lb. ft. (11.08 kg. m.) torque at 2,200 r.p.m. Scientifically designed detachable CYLINDER HEAD with correctly positioned sparking plugs assures high performance, whilst the one-piece CYLINDER BLOCK and crankcase imparts maximum strength and rigidity. VALVES held in detachable guides are operated through push-rods and rockers by a stiff three-bearing CAMSHAFT with harmonic cams, which is driven by a double roller chain from the crankshaft.Balanced CRANKSHAFT of forged steel is supported in three large steel-shell white metal lined bearings, with crankpin bearings of the same type. Low expansion aluminium alloy PISTONS with fully-floating gudgeon pins have two compression rings and one oil control ring, all above the gudgeon pin. Complete high pressure LUBRICATION is maintained by a large capacity oil pump to all bearings. Efficient oil filtration is provided, and detachable plugs fitted to crankcase oilways assist cleaning.Sump capacity is 8 Imperial pints (4.54 litres). 'Solex' downdraught CARBURETTOR, with efficient air-cleaner and exhaust heated 'hot spot' giving easy starting, high performence and fuel economy, is fed by an 'A.C.' mechanical pump from a 9 Imperialgallon (41 litres) tank mounted transversely behind the rear axle. IGNITION system includes high voltage coil of the oil-filled type, 14mm. sparking plugs of the wide gap type, distributor with centrifugal and vacuum-operated automatic spark control ensuring correct timing at all speeds, and separate suppression equipment. Adequate COOLING is maintained by a self-adjusting, leak-proof pump, assisted by a four-bladed fan, giving a vigorous air flow through a robust and efficient radiator core. 'By-pass' thermostat regulates engine heat. petrol power unit