In 1931 at the height of the Great Depression, the last thing any motorcycle company could afford to do was the kind of spending it would take to produce an all-new model.

Yet that's exactly what Harley-Davidson officials approved when they green-lighted the new-from-the-ground-up Model E. When the finished machine was released five years later, that decision proved to be one of the company's smartest ever.

HD's survival was riding on the new Model E and the gamble was huge. At the time the Motor Company's lineup consisted of a smaller single-cylinder bike plus a couple of aging Flatheads displacing 45 and 74 cubic inches (about 750cc and 1,200cc, respectively). The target was a sports bike with the light weight of the 45 coupled with power rivaling the 74.

The engineering required to achieve that goal was impressive. The old side-valve design was replaced with the first overhead valves to appear on a production Harley V-twin, operated via pushrods from a single, multi-lobed camshaft. Interestingly, the valves were set at right angles to each other; an idea taken from aircraft engines of the day. A recirculating oil system with a dry sump was used and the new motor was coupled to a four-speed gearbox via a chain primary drive.

The result was a good looking, reliable powerplant that produced a claimed 37 horses in the base Model E, and 40 in the higher-compression Model EL.

When it was released in 1936, it was the awesome appearance of the new engine that attracted attention. The prominent rocker boxes, looking for all the world like knuckles on a fist, quickly earned the engine the nickname of the "Knucklehead."

The Model E's reputation skyrocketed when racer Joe Petrali took a tuned EL to a record 136.183 mph at Daytona and Fred Ham rode an astonishing 1,825 miles in 24 hours on a standard model E.

At a time when Excelsior-Henderson was getting out of the motorcycle business and Indian was struggling to survive, the modern Knucklehead raised H-D to America's premier motorcycle company, forming the basis for Pans, Shovels, Evos and Twincam motors that followed... taking the company all the way into the 21st century.

The Gamble has paid off in spades.