Parallel x2: Thoughts From the Saddle of a 1951 Ariel Square Four

‘Now that it’s out and running, be sure you run it,’ the 1951 Ariel’s owner said with a wink before sending me on my way, but I was feeling out of my element riding the Ariel Square Four. The shifter’s on the right and shifts backward, feedback from the brakes is vague at best, and the engine was puffing smoke since waking from hibernation.

‘I’ll just tool it around for a bit,’ I thought. But the character of this peculiar four-cylinder revealed itself on the open country roads—and what a lovely alloy lump it is.

It may seem like an oddity today, but a 2×2 four-cylinder engine was definitely a novel concept when Edward Turner first sketched the idea in 1928. Working as a motorcycle dealer and building bikes of his own on the side, Turner wanted to design a next-generation powerplant with higher output and long-haul touring ability. There was a stigma against four-cylinder engines, though, in that transverse fours were considered too wide, and longitudinal engines were too long.

Taking inspiration from your average twin, Turner designed a four-cylinder consisting of two parallel twins in a single case, with one right behind the other. And while it sounds a bit complex, the idea had merits far beyond the packaging, as the counterrotating cranks and four pistons would offset each other and run quite smoothly.

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By: Dean Larson
Title: Parallel x2: Thoughts From the Saddle of a 1951 Ariel Square Four
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Published Date: Fri, 06 Oct 2023 17:00:05 +0000


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