This manual covers Big Twin motorcycles produced between 1940 and 1947. These models, often referred to as the "Knucklehead" era, represent a significant period in the brand's history, known for their robust engineering and distinctive V-twin powerplants. The Big Twin platform, encompassing engine variants like the 61 and 74 cubic inch Knuckleheads, provided the core performance and reliability that defined the marque for decades. This documentation is essential for understanding and maintaining these iconic machines, which were manufactured in Milwaukee, Wisconsin, and continue to be celebrated for their classic American design and enduring appeal. This Factory Service Manual is your definitive guide for the comprehensive service, repair, and restoration of your 1940-1947 Big Twin. Within its approximately 500 pages, you will find detailed instructions covering all major systems, including engine overhaul, transmission service, electrical diagnostics, chassis maintenance, and fuel system adjustments. The manual provides step-by-step procedures, troubleshooting charts, and precise technical specifications, including part numbers and lubrication recommendations, crucial for accurate work. Whether you are performing routine maintenance or a complete engine rebuild, this manual equips owners and technicians with the factory knowledge needed to preserve the integrity and performance of these historic motorcycles. 🏷️ Basic Information Identification Make: Harley-Davidson Model: Big Twin Model Years Covered: 1940, 1941, 1942, 1943, 1944, 1945, 1946, 1947 Platform Name: Harley-Davidson Big Twin (pre-FL series designation) 👋 Introduction Market Position Target Audience: Harley-Davidson enthusiasts, restorers, mechanics, and owners of 1940-1947 Big Twin models. Competitive Analysis Manual Value Proposition: Provides access to the exact factory procedures and specifications used by Harley-Davidson technicians, crucial for accurate restoration and maintenance of these vintage machines. Key Features Essential Resource: The definitive guide for maintaining, repairing, and restoring Harley-Davidson Big Twins from the 1940-1947 production years, a critical period for the brand. 📋 Manual Details Coverage Areas Primary Coverage: Service, Repair, Workshop Page Count Estimated Page Count: 500+ Manual Type Manual Type: Factory Service Manual Language Language: English Format Format: PDF Download 📖 Manual Coverage Systems Covered Engine Systems: All aspects of engine operation, overhaul, and tuning for Big Twin models including the Knucklehead (E, F, EL, FL, UL, ULF) variants. Transmission Systems: Service and repair of the 4-speed constant mesh transmission, including clutch, primary drive, and shifting mechanisms. Electrical Systems: Wiring diagrams, ignition system (battery/coil, magneto if applicable for certain earlier models), lighting, charging system (generator), and accessory circuits. Chassis Systems: Frame inspection and repair, suspension (forks, shocks), steering, brakes (mechanical drum), wheels, and bearings. Fuel System: Carburetor (e.g., Linkert M-series) disassembly, adjustment, and troubleshooting; fuel tank and fuel line service. Bodywork Fittings: Fender service, tank mounting, seat attachment, and accessory mounting procedures. Procedures Included Maintenance Procedures: Regular scheduled maintenance, lubrication, cleaning, inspection, and adjustment procedures for all major components. Disassembly Reassembly: Step-by-step instructions for complete disassembly and reassembly of engine, transmission, and other key assemblies. Troubleshooting Diagnostics: Detailed diagnostic charts and procedures for identifying and resolving common mechanical and electrical issues. Engine Rebuild: Complete engine overhaul instructions, including cylinder boring, piston installation, crankshaft balancing, valve seat grinding, and assembly tolerances. Carburetor Tuning: In-depth guidance on adjusting and rebuilding various Linkert carburetor models prevalent during this era. Electrical Component Testing: Methods for testing and diagnosing generators, ignition coils, distributors (if applicable), and switches. Technical Depth Depth Of Coverage: Comprehensive, covering from basic maintenance to complete engine and transmission overhauls, including detailed specifications and tolerances. 📊 Manual Specifications File Format Digital Format: PDF Print Quality Scan Resolution: High-resolution scans suitable for screen viewing and printing. Binding Type Binding For Digital: N/A (Digital format) Paper Type Paper Type For Digital: N/A (Digital format) Searchability Text Searchable: Yes (typically OCR-processed for search functionality) ⚙️ Engine Specifications Primary Engine Engine Family: Knucklehead (and early overhead valve variants leading into the Panhead era, though this manual focuses on Knucklehead) Engine Variants Common Displacements: 61 cubic inches (1000cc) and 74 cubic inches (1200cc), with some 80 cubic inch (1300cc) UL models also covered under the 'Big Twin' umbrella. Performance Horsepower Torque: Specific figures vary by year and displacement, but typical for the era are in the range of 25-35 HP and corresponding torque figures. The manual will provide exact OEM specs. Fuel System Carburetor Type: Primarily Linkert M-series carburetors (e.g., M3, M5, M8). Ignition System Ignition Type: Battery and coil ignition system, often with a distributor. Cooling System Cooling Method: Air-cooled 🔧 Transmission Standard Transmission Type: 4-speed, constant mesh manual transmission. Optional Optional Transmission: N/A for these model years; 4-speed was standard for Big Twins. Features Clutch Type: Dry clutch, multi-plate. Primary Drive: Chain drive (single row or duplex depending on specific model/year). 📐 Dimensions Exterior Wheelbase Range: Typically around 57-60 inches, depending on specific Big Twin model (e.g., EL, FL, UL). Weights Dry Weight Range: Approximately 550-650 lbs (250-295 kg) depending on model and equipment. Wheels Tires Wheel Size: Commonly 16-inch or 18-inch...