This comprehensive service repair manual covers Harley Davidson Knucklehead Flathead motorcycles manufactured from 1937 to 1947. It provides detailed instructions and illustrations for all aspects of repair, service, restoration, maintenance, rebuilding, and diagnosis. The manual includes information on both OHV 61ci and 74ci engines, as well as Side Valve 74ci and 80ci engines. It offers step-by-step instructions, troubleshooting guides, and exploded views of components. This manual is the same one used by professional technicians and mechanics, making it the perfect resource for DIY enthusiasts. It covers a wide range of topics including: * Engine disassembly and reassembly * Cylinder head and valve work * Piston and connecting rod replacement * Transmission and clutch repair * Electrical system troubleshooting * Fuel and ignition systems * Chassis and suspension maintenance * Bodywork and paint * And much more. This manual provides you with the essential information needed to perform any repair or maintenance task on your Harley Davidson Knucklehead Flathead motorcycle.

The Harley-Davidson Knucklehead, formally known as the WL, was a motorcycle engine produced by Harley-Davidson from 1936 to 1947. The engine's nickname comes from its distinctive "knuckle" shaped rocker arm covers. The Knucklehead was a significant advancement over Harley-Davidson's previous flathead engine, the "45" series. It featured a new, overhead valve design that offered increased power and efficiency. This overhead valve design, with its complex rocker arm system, required a more robust engine casing and resulted in the "knuckle" design so synonymous with this model. The Knucklehead was offered on a variety of Harley-Davidson models, including the WL, WLA, and EL. The WL model, with its 45-cubic-inch engine, was the most popular and was used by the U.S. Army during World War II. The WLA (for "Army") was a militarized version of the WL, featuring modifications like a larger fuel tank, military-style paint, and a rear luggage rack. The Knucklehead engine was known for its power and reliability. The overhead valve design provided a significant increase in horsepower over the previous flathead engines, and the engine was also built to withstand the rigors of demanding use. However, the Knucklehead engine was also known for its complexity, and its maintenance could be quite involved. The engine was also somewhat noisy due to the rocker arm system, but this became part of the Knucklehead's charm for many riders. The Knucklehead was the first engine in Harley-Davidson's history to feature a hydraulically operated clutch, meaning it offered smoother and more reliable shifting. It also introduced a fully enclosed transmission, which was a significant departure from previous models and offered better performance and durability. While the Knucklehead was produced for only 12 years, it left a lasting legacy. Today, the Knucklehead is a highly sought-after motorcycle engine amongst collectors and enthusiasts. Its iconic design, historical significance, and unmistakable roar continue to captivate riders and fans alike.