Although it has a capacity of 1,000 c.c., the new four-cylinder Ariel engine is remarkably compact. The two crankshafts are geared together, and the camshaft is driven by a Welle-tensioned chain, which also drives the Magdyno. Note the bolted-on exhaust manifold and the valve gear arrangement

The Motor Cycle, December 5th 1935, Page 779

Ariel Square Four