Harley-Davidson EL61 Knucklehead
With Ian Falloon
In the early 1930s, the United States was in the midst of the Great Depression and like all motorcycle manufacturers Harley-Davidson was struggling to keep producing and selling high-powered machines.
By 1933 the company was operating at 20% capacity, but optimism prevailed and a new overhead valve motor was developed to replace the side valve. This is a 61-inch (1000 cc) Knucklehead engine, Harley’s first production overhead valve. Originally intended for a 1935 release, development delays eventually led to it appearing in 1936 on the E and EL 61.
Harley created the new overhead valve engine from scratch, including a single camshaft with four lobes to reduce noise. As on most British overhead valve engines today, the valve stem and springs were exposed, resulting in nasty oil leaks.
The newly designed rocker’s case has earned the nickname ‘Knucklehead’. Sitting on top of the double cylinder, the molded shape resembles a closed fist with the “knuckles” exposed. Lubrication is a dry storage tank and a hemispherical combustion chamber that places the valves at a 90-degree angle to each other.
Compared to the previous side-valve engine, the Knucklehead delivers more power; 37 hp for the E and 40 hp for the higher compression EL. The new engine also accentuates the 61’s muscular, stylish look. Polished rocker boxes and thrusters produce horsepower, and a sturdy dry clutch and four-speed transmission ensure that power can be use to be.
But it wasn’t just the engine that created the breakthrough for Harley. From the shape of the fuel tank to the modern front fork, the new model brings a fresh look to the venerable brand.
Rolling on 18-inch wheels, the seat height is just 660 mm, and the frame provides a clear straight line from the rear axle to the handlebars. But Knucklehead isn’t just handsome. Despite weighing nearly 270 kg when fully wet, the top speed remains at 160 km/h.
In the late 1930s, the Sixty-One overhead valve started to have an old look and by 1940 the style was improved upon. Outside, the entire car has been reworked to give it a tougher, cleaner and more modern look.
This look will style Harley’s Big Twins, not only during the war years, but also with the next-generation Panhead. This classic style was also revived on the Heritage Springer Softails of the 1990s. New for the 1941 EL was the ‘airplane style’ speedometer with reset odometer and rocket fin muffler.
This year, Harley also fitted a new oil pump and a slightly smaller Linkert carburetor to create a smoother ride at low speeds. To overcome the clutch sticking and pulling, the 1941 EL received a completely new clutch. The 1941 Knucklehead was the last civilian Harley until 1945 when the company focused on military projects.
But the Knucklehead is arguably the most important motorcycle in Harley’s history. Knucklehead is the right machine at the right time. Harley-Davidson managed to survive the downturn, and Knucklehead initiated a new chapter for the company.
Without this motivation, the company would not be able to survive for long. Compared to modern production levels, Knucklehead production is relatively modest. This, combined with a few that have been around for more than 80 years, has made the Knucklehead one of the most desirable and sought-after production Harley-Davidsons.
Five facts about Harley Knucklehead
- In March 1937, Joe Petrali in an EL 61, set a new top speed record of 136 mph (219 km/h) at Daytona Beach, eclipsing the previous record set by the Indians. create.
- Soon after, Fred Ham set a new 24-hour record at Muroc Dry Lake in California. He traveled more than 1,825 miles (2,937km) at an average speed of 76 mph (122 km/h).
- The E and EL 61 were much more successful in 1936 than Harley predicted. With nearly 2,000 units produced, demand has outstripped production capacity.
- In 1941, a larger OHV stable mate, the 74 cubic-inch Model F and FL, joined the Sixty-one. Boring and stroking Sixty-one achieve greater capacity. The 74 immediately became more popular followed by the 61, with 2608 units sold, compared with 2541 smaller 1000 units, in 1941.
- After 11 years of operation, the Knucklehead was finally completed in 1947, replaced by a Panhead engine with aluminum head and hydraulic lifter.
