1971 Healey 1000/4, Prototype #2. Owner: Thomas Harper, Garden Grove, California.

This has to be one of the least-known motorcycles built since the end of World War II, with an Ariel 4G Mark II Square Four engine bolted into a Roger Slater frame. The photo model is one of the two prototypes, and lacks some of the amenities of the production versions – such as the side panels.

The Healey 1000/4 does not appear to be listed in any of the popular motorcycle encyclopedias, and the only major mention to be found in motorcycle histories are some three pages in Roy Bacon?s “Ariel – The Postwar Models.” I remember reading something about it in an American motorcycle magazine in the early 1970s, but that is about it. After punching a few keys on my computer a dozen different sites come up, with varied information. Any number of articles have probably been written about this bike in British magazines, but apparently those stories are not online.
Starting at the beginning means back to the first 997cc OHV Ariel 4G engine. An earlier, smaller, OHC version existed, but we?ll leave that out. That 4G was around from 1936 to 1959, with Ariel advertising Squariels that last year, along with the new two-strokes.

1971 Healey 1000/4, Prototype #2

The biggest problem with an air-cooled square four is that the front cylinders do fine, but the rear pair can overheat. Over the quarter-century of the 4G?s production – minus a couple of years due to the ...