Model Years Covered:
1940, 1941, 1942, 1943, 1944, 1945, 1946, 1947
Platform Name:
Harley-Davidson Big Twin (pre-FL series designation)
Target Audience:
Harley-Davidson enthusiasts, restorers, mechanics, and owners of 1940-1947 Big Twin models.
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.
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.
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.
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.
Depth Of Coverage:
Comprehensive, covering from basic maintenance to complete engine and transmission overhauls, including detailed specifications and tolerances.
Engine Family:
Knucklehead (and early overhead valve variants leading into the Panhead era, though this manual focuses on Knucklehead)
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.
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.
Carburetor Type:
Primarily Linkert M-series carburetors (e.g., M3, M5, M8).
Ignition Type:
Battery and coil ignition system, often with a distributor.
Cooling Method:
Air-cooled
Wheelbase Range:
Typically around 57-60 inches, depending on specific Big Twin model (e.g., EL, FL, UL).
Dry Weight Range:
Approximately 550-650 lbs (250-295 kg) depending on model and equipment.
Wheel Size:
Commonly 16-inch or 18-inch wheels.
Tire Sizes:
Varies by year and model, but typical front could be 5.00x16 or 5.50x16, rear 6.00x16 or similar. Manual will specify exact fitments.
Bolt Pattern:
Not applicable in the same way as modern cars; wheel hubs are specific to Harley-Davidson design.
Oil Change Interval:
Typically every 1,000-1,500 miles or annually, depending on usage. Manual will provide precise recommendations.
Major Overhaul Interval:
Engine overhauls are typically based on mileage (e.g., 20,000-30,000 miles) or symptoms of wear. Manual will detail wear limits.
Engine Oil Type:
Primarily straight-weight mineral oils, such as SAE 50 or SAE 60 (e.g., Harley-Davidson's own HD-1 or similar high-detergent oil). Manual will specify exact grades.
Transmission Oil Type:
Gear oil, often SAE 90 or SAE 140. Manual will specify exact type and quantity.
Primary Chain Case Oil:
Specific lubricant, often a dedicated primary chain oil or SAE 50/60. Manual will specify.
Knucklehead Specific Issues:
Valve seat wear, oil leaks (inherent to vintage engines), potential for cam lobe wear, and carburetor adjustment sensitivity. Manual provides solutions.
Transmission Wear:
Synchronization issues in the 4-speed transmission over time; manual details adjustment and rebuild.
Part Number Reference:
Manual includes detailed part numbers for all components, crucial for sourcing correct replacement parts.
Grease Points:
Specific greasing schedules and locations for wheel bearings, steering head bearings, and suspension linkages detailed in the manual.
Harley Davidson Legacy:
Harley-Davidson has a storied history dating back to 1903, with Big Twins forming the backbone of their motorcycle lineup for decades.
Knucklehead Era:
The 1940-1947 period represents the latter half of the highly regarded 'Knucklehead' era, known for its distinctive valve covers and robust engineering.
Manufacturing Location:
Milwaukee, Wisconsin, USA.
Wartime Production:
Production during WWII (1942-1945) was significantly impacted, with much of the factory's output dedicated to military contracts (e.g., WLA models). Civilian production was limited.
Model Significance:
The Knucklehead Big Twins are iconic and highly sought after by collectors and restorers for their historical significance and classic American V-twin character.
Vintage Appreciation:
Consistently ranked among the most desirable vintage Harley-Davidsons.
Oem Documentation Standard:
Represents the official factory service documentation standard for its era.
