Ariel 1947 model 4G 997cc Square Four frame # XP 1573 engine # DK 738
Ariel unveiled the all new 500cc SQ 4 to the motorcycle world at the Olympia show in 1930. It was the brainchild of design genius Edward Turner and was powered by an OHC engine with 2 parallel crankshafts, mounted in a crankcase transversely across the frame. The two cranks were geared together in the center of the unit, so in effect there were two vertical twin engines running in opposite directions. The result was a silky, smooth power output with instant response to the throttle. In 1932 the capacity was increased to 600cc and in 1937 a new 4 appeared, this time of 997cc and with pushrods instead of the chain-driven overhead cam. This new model was labelled 4G. Roller conrod bearings were also dropped in favour of plain bearings and the coupling gears were moved from the center of the engine and placed in a case on the left side. Bore x stroke were 65 x 75 mm. Power output was about 36 HP, top rpm approx. 5800 and a single Solex carburettor was fitted. The engine proved to be extremely flexible: it would pull in top gear from 12 mph to more than 90 without any protest. In 1939 a new spring frame was added, and after WW2 new telescopic front forks. In the first years after the war the 4G was fitted with rigid rear end only. In 1948 a revised model, the Mk. I was brought out, in which the iron cylinder head and block were replaced by aluminium alloy and magneto ignition was replaced by coil. Also the “1000” on the timing cover was changed to “Square Four”.
This last year 4G is an older (unfinished) restoration that comes with comfortable Lycetts saddle, valanced front mudguard and tank top instrument panel with 140 km Smiths speedo, inspection lamp and “Ariel” 8-day clock. This impressive and luxurious machines is outfitted with a chromium petrol tank and practical prop stand.