One of the most desirable bikes on the planet is the Ariel Square Four. It’s named for the absolutely unique engine design which is basically two parallel twins in the same engine case. The flywheels for both twins were directly geared together which made for some complex plumbing and mechanicals.
The square four was introduced in 1931 and by 1950 had evolved into an air cooled 997 cc (60.8 CID) overhead valve engine. Considerable changes in the alloys used and head configuration had all but eliminate the square four’s tendency to melt the rear pistons that had plagued the motor from the start.
Alloy usage dropped the weight of the 1950 to roughly 440 pounds by 1950. With a single carb and 35 hp the 4 speed square four was capable of better than 90 MPH. While not quite up to the Vincent standards for speed, the Square Four was considered fast and elegant.
This particular bike is for sale on here on Cycle Trader for $11,900 in San Jacinto, CA and seems to fit into the ‘unrestored original’ class. Note that the original mufflers are included if you want to replace the trumpets as installed.
I think it’s a way cool bike. I’m buying a lottery ticket, just in case.