1947 Harley-Davidson EL 61

It is perhaps one of the most coveted types of American Classic motorcycles in existence.

The 61 cubic-inch E, ES and EL Harley-Davidson models ushered in the transition from the long-serving but under-powered side-valve flathead V-twin engine to the higher tech and higher powered overhead valve pushrod engines.

While the new 61 E series model included a number of other product innovations when it was introduced in 1936, it was its distinctive engine that gave it an unmistakable appearance and unbeatable nickname: the “knucklehead.”

The polished rocker covers to many resembled huge clenched fists to give the motor its name. Indeed, today many enthusiasts can instantly identify a knucklehead when they see one, but fewer recall the model designations that applied.

In the context of the turbulent times it was born into, the introduction of any new model motorcycle had to seem like small potatoes. The world was still in the swoon of a great economic depression, fascism gripped much of Europe, war clouds were gathering in both Europe and Asia, and FDR was doing his best to keep the country from starving.

But, as time went on and things got better, the knucklehead models attained ever-increasing status as performance machines. That status was urged on by some record-setting performances.