1955 Ariel Mark II Square Four
VIN:
The Ariel motorcycle company is revered among classic motorcycle enthusiasts for its iconic and unique “Square Four”, featuring a revolutionary four cylinder engine arranged in a square configuration in which two pairs of cylinders, each pair with its own crankshaft, were arranged one behind the other. The two crankshafts were synchronized with a straight cut gear that created a distinctive “growling” sound of an Ariel Square Four at idle.
The example you see here is a 1955 “Mark 2” model, one of 3,828 Square Fours built between 1953 and 1958, and marked the culmination of Ariel's Square Four technology. Featuring all new alloy cylinder heads and four separate exhaust pipes, and boasting 1,000 cubic centimeters and 44 horsepower and mated to a four speed transmission. The Mark 2 was renowned for its smoothness and broad power band, so much so that the company bragged that it could go from 10mph to 100mph using top gear alone. Only a few hundred Mark 2s were built in 1955, making this a particularly rare example, and it is believed to be the only licensed and registered Mark 2 Square Four in Montana.
This machine came to American shores in 2006, where it was purchased by the current owner and transported to Los Angeles where it underwent a complete restoration by renowned Ariel Specialist Chuck Walton. The engine and transmission were rebuilt, and a high volume Morgo oil pump and an oil cooler were added, while the bike was repainted in its original maroon color. (All work docs included with sale)
The Ariel showed 64,335 miles on the odometer when it was purchased in 2006. The current owner has ridden it sparingly for a total of 1,500 miles since, with oil changes and minor maintenance performed at 500, 1,000, and 1,500 miles, following the original restoration at 64,335 miles.
Left unpainted is the wind splitter atop the front fender, which displays what is believed to be the machine's original plate number. The back license plate is a vanity plate that displays the same number as that found on the wind splitter, and can be left with the bike at new owner's request. Other items included with the sale are misc. rubbers/boot, handlebar grips, air cleaner, mirrors, and extra battery box.
THIS MOTORCYCLE TO BE COLLECTED FROM HELENA, MONTANA.
The Motorcycle has been consigned to the Classic Motorcycle Online Auction hosted by the Classic Car Auction Group. The auction is Saturday, May 9, 2026, with online bidding only. To consign your motorcycle and/or to register to bid on this and other bikes in the auction go to http://www.classiccarauction.us.
