Ariel 1938 model 4G 997 cc Square Four frame # F 870 engine # DK 637
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.
Bore x stroke dimensions are 65 x 75 mm and the compression ratio is 5.8:1. The Four has a single rear-mounted Solex carburetor and a four speed foot change gearbox.
The fuel tank holds 18 litres and the dry weight of the machine is 191 kg. The engine delivers its maximum 36 bhp @ 6,000 rpm, resulting in a top speed of 150 plus km.
This luxurious touring mount is fitted with a number of extras such as jiffy stand, pillion seat and luggage rack.
The engine is very reliable: there’s a Morgo oil pump on board, the magneto has been rewound recently and the conrods are fitted without babbitt.
This SQ4 has been in regular use and is in excellent shape throughout.