KNUCKLEHEAD * 1936 - 1947 The Harley-Davidson
Knucklehead made its unsurpassed beauty in 1936. Competition experience heavily influenced the engine and it made a
great appearance on the sand in Daytona Beach, Florida by posting a speed of 136.183 mph, a record which still stands. The first Knucklehead engines were available with a 61 cubic inch (989
cc) in three specifications: The Knucklehead EL engine put out more than 40bhp at 4,800 rpm, a big increase in performance over
the sluggish side valves. But there were initial problems. The dry sump lubrication system was the worst concern
because some parts got too little oil and others got too much, including the pavement underneath the bike. The problem
was solved with the 1941 74 cubic inch Model F Knuckle using a centrifugally controlled oil pump by-pass. Even though
the Knucklehead engine notoriously leaked through its many external seals and separate primary drive oiling, many riders would
prefer the big Knuckle's oil system in very hot conditions to that of the later, "improved" Panhead. Due to competition from large capacity Indian Motorcycles V-Twins, Harley-Davidson responded with the bigger Knuckle engine, but the extra torque demanded a new seven-plate clutch instead
of the old five-plate, giving 65% greater friction area. Also added: - bigger rear brake
- "airplane
style" speedometer
- larger, more efficient
air-cleaner
Lore has it that the best of the big
Knucklehead engines were those built in the final pre-World War II years, but few 74 cubic inch (1,207 cc) Knuckleheads hit the road until 1947.
The Harley-Davidson Knucklehead engine was named after the
distinct shape of the rocker boxes which resembled inverted baking pans. The engine is a 45 degree, two-cylinder V-Twin engine with push rod activated overhead valves, two per cylinder. It was the third basic type of V-Twin engine used by Harley-Davidson, replacing the Flathead engine of the VL Knucklehead in 1936 as Harley-Davidson's top-of-the-line
model. As the design of Harley-Davidson engines
has evolved through the years, the distinctive shape of the valve covers has allowed Harley enthusiasts to classify an engine
simply by looking at the shape of the cover. A
Knucklehead engine has round knobs on the cover resembling knuckles, thus its name.
Almost every chopper enthusiast is aware of the Harley-Davidson
Knucklehead engine. Its original name was the 61 OHV. To many motorcycle fanatics, whether they are chopper
or stock configurations fans, the Harley-Davidson brand name is synonymous with cool, powerful, quality motorcycle engines,
accessories and parts. Frequently, anyone building a chopper will to a Harley-Davidson power train because of the company's
excellent reputation as well as for the prestige associated with owning a Harley-Davidson V-Twin custom chopper. The Harley-Davidson Motorcycle Company initially introduced the Knucklehead
engine in 1936. Prior to 1936, Harley-Davidson had manufactured overhead valve singles but the 1936 Knucklehead
represented the first of the overhead valve V-Twins. The 1936 through 1940 models displaced 61 cubic inches. In
1941, a 74 cubic inch displacement version was added. These engines were more powerful than the previous Flathead engine.
Flatheads produced about 30 to 35 bhp while the Knucklehead generated 40 horsepower in the 61 cubic inch and 45 horsepower
in the 74 cubic inch models, offering noticeable extra punch. The Knucklehead also introduced
Harley-Davidson's more moder recirculating oil system. This was a significant development, replacing the messy, inconvenient
total loss setup of previous models. However, the Knuckleheads continued to experience oil leakage, but this was still
a big improvement. It is notable that the research and development phase occurred during
the Great depression, and the Knucklehead led to the V-Twin engines which followed, even those in production today. With the advent of the popularity of custom Choppers, the Knucklehead engine became popular choice form many Chopper motorcycles. These powerful engines were chosen by many to place into stretched, raked frames and over-stock length
forks. Today, the Knucklehead engine is a classic and anyone lucky enough to have one has a treasure to be truly
proud of. Even as a basket case which must be completely rebuilt, the Knucklehead engine is a great choice for powering
your custom Chopper. These engines, when given proper care, can increase in value while providing a truly classic Chopper to enjoy.
|
