This comprehensive service manual for the 1940 Harley Davidson Knucklehead motorcycle is designed to empower both professional technicians and dedicated DIY enthusiasts with the knowledge and guidance needed to perform a wide range of repairs and maintenance procedures. It equips individuals with the essential skills and understanding of electrical and mechanical concepts necessary to confidently tackle various tasks. This manual is structured to provide clear and detailed instructions, making the repair process accessible even for those with limited experience. It covers a wide array of topics, encompassing everything from routine maintenance to complex engine overhauls. Within its pages, you'll find a wealth of information, including step-by-step repair procedures, critical specifications, and illustrative diagrams. You'll gain insight into dismantling, assembling, cleaning, and reinstalling components, ensuring a thorough understanding of each process. The manual also provides valuable guidance on troubleshooting common issues, helping you diagnose and resolve problems effectively. With this service manual, you'll gain a comprehensive understanding of your 1940 Harley Davidson Knucklehead, empowering you to maintain and repair it to factory standards.

The Harley-Davidson Knucklehead, produced from 1936 to 1947, was a revolutionary motorcycle that marked a significant shift in the evolution of Harley-Davidson's design and performance. It was named for its distinctive "knuckle" shaped rocker arm covers, which housed the valve actuating mechanism. The Knucklehead engine featured a redesigned cylinder head with a hemispherical combustion chamber, which improved combustion efficiency and increased power output. This innovative design, along with the introduction of hydraulically operated valves and a new, more robust transmission, made the Knucklehead a true performance machine for its time. The Knucklehead also featured a longer wheelbase, providing better stability and handling. Its sleek, streamlined design and powerful engine captivated riders, establishing it as a symbol of both luxury and power. The 1940 Harley-Davidson Knucklehead continued to refine the design and performance established by its predecessors. The engine, a 45 cubic inch (740 cc) V-twin, was further optimized for efficiency and power, delivering a smooth and responsive ride. The motorcycle's distinctive "fishtail" exhaust pipes, the classic teardrop-shaped fuel tank, and the distinctive "knuckle" covers all contributed to the Knucklehead's iconic aesthetic. The 1940 Knucklehead was available in a variety of configurations, including the EL (for "Electra" - which featured an electric starter) and the UL (for "Ultra" - which was a more streamlined model with a smaller fuel tank and a lower seat). Regardless of the specific model chosen, the 1940 Harley-Davidson Knucklehead offered a blend of classic styling, exceptional performance, and enduring quality that continues to inspire enthusiasts today.