The Ariel Square Four design goes all the way back to 1931, soon after Edward Turner designed an interesting new four-cylinder motorcycle engine formed from two OHC parallel twins. The design became known as the square four engine, and lent its name to this Ariel motorcycle.
By 1953, the Ariel Square Four had already gone through a few revisions, and was formally known as the Mark II. The Mark II featured a 997 cc engine. Upgrades to the powerplant included separate barrels, a new cylinder head, and four exhaust pipes, which bumped up horsepower to 40. This enabled the Square Four to ‘do the ton’, even with a curb weight of 425 pounds.
This example is an older restoration that was re-freshened (rebuilt engine, gearbox, and generator) about 120 miles ago. It’s claimed to run like a new ’57 bike. Find this Ariel Square Four Mk II for sale in Tacoma, Washington with bidding up to $10,755 and the reserve not yet met