Ariel 1950 Square Four Mk I 997cc combination frame # CW 697 engine # JJ 705
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 early Mk I was first registered on August 2, 1950 and her first owner was a Mr. G.W. Wood from Huddersfield in West Yorkshire, England. She was restored some years ago by an Ariel enthusiast and fitted with a graceful Stoye sidecar. The combination has been used regularly for club runs and is in excellent condition throughout. She comes with tank top instrument panel with amp gauge, oil pressure gauge, inspection light and light switch. A 125 mph Smiths speedo is fitted as are convenient handlebars for sidecar riding. The original bars come with the machine and also an information file with 1950 Owners’ Guide and technical and restauration notes and invoices.