1946 Harley Davidson knucklehead

The knucklehead is a retronym used by enthusiasts to refer to a Harley-Davidson motorcycle engine, so named because of the distinct shape of the rocker boxes.^[1] The engine is a two-cylinder, 45 degree, pushrod actuated overhead valve V-twin engine with two valves per cylinder. It was the third basic type of V-Twin engine used by Harley-Davidson, replacing the Flathead-engined VL model in 1936 as HD’s top-of-the-line model. The engine was manufactured until 1947 and was replaced by the Panhead engine in 1948. The Knucklehead-engined models were originally referred to as “OHVs” by enthusiasts of the time and in Harley’s official literature; the nickname arose from the California chopper culture of the late 1960s. Wiki

__________________

Production of the Knucklehead continued into World War II. In 1942, Harley-Davidson began to fit improved crankcases, or long-rib cases, since dealers had reported breakage problems with the earlier short-rib cases. Typically a crack would form on the left-hand crankcase, unfortunately, the same side that carried the serial number. Harley-Davidson even built a few experimental 3-wheelers fitted with the Knucklehead engine. Civilian production began again in 1944 with a few models designated for crucial positions. If you were a doctor and needed transportation, you could be moved to the top of the list; however, the general population would have to wait. Harley-Davidson was offering low- and high-compression versions of its 61 CI and 74 CI engines. The higher-compressions model were then designated by a suffix L on their serial number. Civilian production was underway by 1946, and by the next year, Harley-Davidson had ramped up production to approximately 12,000 units, making numerous small changes for the 1947 model year.

In the early days before World War II, Milwaukee-based Harley-Davidson sent test riders of new models out into the wooded hills of rural Wisconsin. The experimental models were unmarked, and testers were instructed to stay away from towns and dealerships. The point of all this secrecy was to keep the rumor mill down. The motorcycle world was very small, and even without the Internet or cheap, long-distance telephones, rumors would spread from one end of the country to another faster than a Twentieth Century Limited locomotive. In the case of the Knucklehead, the secrecy had an additional purpose: Harley didn’t want news of its new overhead valve engine to get out before its engineers had fixed its very leaky top end.

1936 Harley-Davidson EL
Top speed: 95mph
Engine: 60.33ci (988.56cc) air-cooled OHV 45-degree V-twin, 3-5/16in x 3-1/2in bore and stroke, 7:1 compression ratio, 40hp @ 4,800rpm
Weight (wet): 515lb (234kg)
Fuel capacity/MPG: 3.75gal (14ltr)/35-50mpg
Price then/now: $380/$75,000-$150,000

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.

This Knucklehead is still getting it done out on the road.

For example, in 1937, factory backed rider Joe Petrali took a partially streamlined twin carburetor EL down the beach at Daytona through the measured mile for a two-way combined average of 136.183 mph, setting a world record!

Later in the year, in an effort to showcase the engine’s reliability, as well as speed, an EL covered 1,825 miles in 24 hours at an average speed of 76 mph, setting a new endurance record.

The E Solo model in the series was the base model with an output of about 37 hp using a compression ratio of 6.5:1; the ES model was the same, targeted for use in sidecar rigs, the EL came with a 7.0:1 compression ratio and that higher compression yielded an output of about 40 hp and was called the Special Sport Solo.

Other features that were introduced with the 61 E series bikes that tended to be overshadowed by the hoopla about its engine configuration and power were things like a pressurized dry sump lubrication system that boosted oil pressure as engine speed increased, a double-cradle frame, moly-steel springer fork, an upgraded clutch and four speed transmission, tank mounted dashboard that included mechanical ammeter and oil pressure gauge and memorable art-deco tank badges and styling.

In 1936 1,704 knuckleheads were produced, 1,526 of which were the hotter EL version, while only 152 of the E and but 26 of the ES versions were built. Imagine making a barn find of one of those precious few 1936 ES versions today!

Changes were coming that would soon compel redesign of the “Knuck.” Once World War II ended in August, 1945, the US economy turned to civilian matters—rural dirt roads were black-topped and more four-lane highways like the Pennsylvania Turnpike were built, allowing motorcyclists to ride faster and farther.

Stefan Erider