Ariel 1939 model 4H 997 cc Square Four frame # AX 446 engine # CJ779
Ariel unveiled the all new SQ 4 to the motorcycle world at the Olympia Show in 1930.
It was a brainchild of design genius Edward Turner and it 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 uf 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 600 cc and in 1937 a new 4 appeared, this time of 997 cc and with pushrods instead of the chain-driven overhead cam.
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.
The 1939 997 cc model was available as 4G in Deluxe specification and 4H in Standard specification.
Some differences were the size of the tank (the petrol capacity of the 4G tank was 17,5 litres, the 4H tank could hold 14,5 litres) and the tyre sizes.
The standard 4H was fitted with 3.25 x 19 fore and aft while the 4G had a more substantial 4.00×18 rear tyre.
Further differences were the quickly detachable rear wheel and fishtail silencers on the 4G.
This machine is a very good-looking specimen of the Standard 4H that has been fitted with a more substantial 4.10×19 rear tyre.
This fine piece of prewar technology has been restored some time ago. The bike has not been run for quite some time and the magneto requires attention.