This comprehensive service repair manual is your ultimate guide to maintaining and repairing your Harley Davidson Big Twins Knucklehead-Flathead motorcycles from 1940 to 1947. It covers every detail of these iconic machines, providing you with the information you need to keep them running smoothly. The manual features detailed illustrations, diagrams, and wiring schematics, ensuring you have a clear understanding of each system. Step-by-step instructions guide you through every repair process, making even complex tasks manageable. Whether you're a seasoned mechanic or a DIY enthusiast, this manual empowers you to tackle any repair with confidence. With its in-depth coverage and easy-to-follow instructions, this service repair manual is an invaluable resource for anyone who owns or works on a 1940-1947 Harley Davidson Big Twins Knucklehead-Flathead motorcycle.

The Harley-Davidson Big Twins, specifically the Knucklehead and Flathead models produced between 1940 and 1947, represent a pivotal era in the American motorcycle industry. These iconic machines, with their distinctive engine designs, marked the transition from the earlier, less refined motorcycles to the more powerful and sophisticated bikes that would define Harley-Davidson's future. The Knucklehead, with its exposed rocker arm design that resembled a clenched fist, debuted in 1936 and quickly gained notoriety for its improved performance and smoother operation compared to its predecessor, the Flathead. The Flathead, though lacking the visual appeal of the Knucklehead, remained a popular choice throughout the 1940s, offering a robust and reliable powertrain, especially for the more utilitarian uses of the time. Both models featured a 74-cubic-inch (1,200cc) V-Twin engine, though the Knucklehead boasted a higher compression ratio, delivering increased horsepower and torque. The 1940-1947 Big Twins, while sharing the same engine core, were distinct in their aesthetics and features. The Knucklehead, with its signature Knucklehead engine design, showcased a more modern look with streamlined fenders, chrome accents, and a more refined overall design. Conversely, the Flathead opted for a more utilitarian approach, with its less pronounced styling and focus on reliability over flashy aesthetics. The war years, however, saw production shifted towards military bikes, with civilian models mostly discontinued. The end of World War II ushered in a new wave of demand for motorcycles, and the Big Twins, while still adhering to their pre-war designs, incorporated some refinements based on wartime experience. These machines continued their legacy as powerful and reliable motorcycles, cementing Harley-Davidson's position as a leader in the motorcycle industry and laying the foundation for the iconic models that would follow.