ARIEL SQUARE FOUR
Edward Turner is probably best known for being the person who, through his Triumph Speed Twin, started the British obsession with ohv parallel twins. However, as most of us know, he'd already created the legendary Ariel Square Four, which effectively placed two parallel twin engines one behind the other with their crankshafts linked by a helical spur gear. Folklore has it that Turner first sketched the four cylinder layout on the back of a fag packet. Some reports suggest that the man himself confirmed the details – it was a packet of Woodbines, apparently!
Turner had offered his design to a number of manufacturers, including the mighty BSA concern, with no success until his efforts were finally rewarded by Jack Sangster of Ariel. The unique configuration of the square four cylinder engine was less wide then the now almost universal design of four cylinders across the frame, and less long than an inline fore / aft design.
So compact was Edward's engine that the prototype was tested in a frame from a 250, although for production it was housed in a 500 frame, matched to a Burman gearbox. The early engine was noted to be very smooth indeed, but
