1939 Ariel 1000 Motorcycle w/ Square Four Engine

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While we may be old school and though many of my friends are rabbis, we’re not orthodox car enthusiasts around here. While I have no intention of imitating Jalopnik’s posts about planes, trains, boats and bikes, the truth is that anything mechanical fascinates me and things with motors and engines engage me even more than simple machines. Also, if you’re a regular reader, you know that we like to feature the unusual rather than the mundane, more Javelins and AMXes than ’69 Camaros. So this post on the 1939 Ariel 1000 motorcycle at the 2012 Eyes On Design show should be no surprise. The Ariel used an unusual engine configuration known as the “square four”, originally designed by Edward Turner in the late 1920s.

Early OHC Ariel square four

Turner arranged the cylinders in an equidistant square, with the front two and rear two cylinders having their own crankshafts with helical gears driving a center mounted flywheel. Each pair of pistons were timed 180 degrees to each other, with the two pairs 90 degrees apart. That meant that when one pair was at top and bottom dead centers, the other pair was mid-stroke. This gave Turner’s four great balance, eliminating vibrations. It also allowed a lot of displacement in a compact powerplant.

To view the entire photo gallery in your choice of 2D or stereo 3D formats, click here for a Flash player or here for an HTML applet

Turner shopped his design around to various British bike makers, getting rejected by BSA but embraced by Ariel and introduced in 1930. Over the years Ariel increased engine capacity and in 1937 switched from Turner’s overhead cam to a pushrod 995cc version as the OHC engines tended to overheat. Later changes would involve an aluminum engine block and head, a move to individual cylinder barrels for better cooling, and an improved head with four individual exhaust ports. In the 1950s, the big Ariel was popular as one of the few bikes capable of “the ton”, reaching 100 MPH. The OHV Ariel square four was in production over the course of over two decades, ending production in 1959. By then Ariel was owned by BSA and the big square four didn’t fit into their plans. Most big bikes in the 1960s were twins or triples. Four cylinder motorcycle engines didn’t again come into vogue until Honda started introducing its 350/500/750 transverse inline fours in the early 1970s.

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