Famed motorcycle designer Edward Turner created the Square Four Engine in 1928. BSA passed on his design, but Ariel started producing the bike in the early 1930s. Ariel manufactured the rare Square Four motorcycle between 1931 and 1959.
A 1958 custom-built Ariel Square Four, converted into a chopper in the 1970s, is now for sale on eBay.
The trend in mid-century European motorcycles was smaller, higher revving engines. Meanwhile, the Ariel Square Four was offered as a heavyweight luxury bike—an alternative to the Vincent meant for gentleman riders seeking something more refined. These motorcycles are sometimes nicknamed the “Squariel.”
Shop now for custom-built choppersThe Square Four design featured two transverse crankshafts—two parallel-twin engines joined by geared central flywheels in a four-cylinder block with a single head.
It’s rare to see an Ariel as a full custom, but it makes a great looking motorcycle. The plunger frame lends itself well to the chopper style. In fact, aftermarket companies like Amen Savior and Santee used Ariel-type designs as the basis for aftermarket frames in the 1970s. The chopper style is characterized by stretched front ends, large king and queen seats, minimal suspension, and wild paint jobs.
This particular bike was on display at a museum in Wisconsin for many years. The motorcycle wasn’t started during those years at the museum. But the seller installed new plugs, wires, points, and new carburetors and fuel lines. The chopper also got fresh rubber. It was also modified for dual carburetors, replacing the original SU carb.
A Tall Frame Style
In 1953, the four-pipe version, the 997cc Square Four Mk II, was released. This version ran until the demise of the model in 1959. It featured a redesigned cylinder head with four separate exhaust pipes stemming from two cast-aluminum manifolds. The bore and stroke sit at 65mm by 75mm, with a compression ratio of 7.2-1. These models had about 40 horsepower and could reach about 100 miles per hour. Getting to that speed could take a while.
The fresh frame style provided clearance for the tall, automotive-type SU carburetor. The wheelbase is 57 inches, with a total weight of about 430 pounds. That’s heavier than most British bikes of the era. The seat height is 31 inches with a ground clearance of about 5.5 inches.
The frame on the Ariel was a plunger rear suspension with a rigid mounted dual seat. Sidecars were available as an option.
These bikes were known for being leak-free due to the horizontally split cases. But they were plagued with cooling problems. The lack of airflow often caused high temperatures in the rear cylinders, sometimes causing warping in the head, leading to faulty head gaskets.
Loaded with Personality
The motorcycle for sale on eBay, unfortunately, doesn’t have provenance. Alas, the builder is not known. The previous owner was an Ariel collector, and the customizations very likely took place in the 1970s.
The bike now features a D&D springer style front end, with the original Ariel plunger rear. The seller notes that some of the paint and chrome aren’t in top condition, but that contributes to the bike’s personality and patina.
This chopper has attractive accents. For example, the king and queen seat leads into a tall, leaned-back Trident-style sissy bar. The coffin tank is accented by blue paint with a dark blue fading into a lighter blue along all body lines. The paint shows some age, but that’s due to being a survivor of the 1970 chopper heyday. It also features a hexagonal oil tank located under the seat in chrome to match the rest of the bike.
The seller states:
It had Lake injectors, which I couldn’t get running right at all, so I tried a pair of PWK knock-off carbs. They’re not the best choice, but it runs strong now. I’m not good with carburetors, so I figured the next owner could upgrade if they choose to. It’s a little hard starting when it’s cold, but after the first start of the day, it fires up first or second kick every time.
If you’re looking for a custom chopper that will get you noticed at bike night, this unique 1958 custom-built Ariel Square Four located in Indiana might have your name on it. It is currently listed at $18,500 with an option to make your best offer. And eBay offers an extensive selection of Ariel motorcycle parts to keep it running in the wild.
