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. Turner had actually shopped his engine design out to other British firms, but BSA rejected it. The bike was produced until 1959, making this example one of the last few out of the factory.
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 specific Ariel Square Four has just under 24,000 miles and is claimed to be an unmolested example that runs well. The seller notes that the seat has been recovered.
Find this Ariel Square Four for sale in Alabama with bidding up to $18,000