The Square Four originally had only two exhaust pipes.
The engine of the 1957 Ariel 4G Mk II motorcycle used the "square four" design, which consisted of two crankshafts geared together and four cylinders arranged in a square pattern, with a pair of pistons tied to each crankshaft.
Instruments were at the top of the headlight nacelle.
The 4G Mk II featured a plunger-type rear suspension.
The 1915 Emblem Twin motorcycle's 76.6-cubic-inch engine was unusually large for its day. It was a bold offering from a company struggling to remain afloat amongst fierce competition and the ravages of an economic recession. Learn more about the 1915 Emblem Twin.
The 1970 BSA Lightning motorcycle battled faster less-expensive Japanese bikes. BSA didn't survive long afterward as the competition from Japan proved too much. See pictures and learn how the BSA Lightning dealt with its rivals.
