Target Audience:
Harley-Davidson owners, restorers, mechanics specializing in vintage motorcycles.
Niche:
Essential resource for maintaining and restoring pre-WWII era Harley-Davidson Big Twin motorcycles.
Alternatives:
Original factory service bulletins, period workshop manuals (rare and expensive), informal online forums (less reliable).
Convenience:
Instant PDF download eliminates shipping delays and costs.
Historical Value:
Provides direct insight into Harley-Davidson's engineering and service practices of the era.
Practical Utility:
Enables owners to perform complex repairs and routine maintenance themselves.
Engine Mechanical:
Detailed overhaul procedures for cylinders, pistons, crankshaft, connecting rods, camshaft, lifters, and valve train.
Engine Performance:
Specifications and troubleshooting for carburetor, ignition timing, and compression.
Transmission Overhaul:
Step-by-step instructions for disassembly, inspection, and reassembly of the gearbox.
Clutch Assembly:
Service procedures for clutch plates, pressure plates, and release mechanisms.
Electrical Diagnosis:
Troubleshooting guides for lighting, ignition, charging system, and basic accessory wiring.
Fuel Delivery:
Maintenance and repair of fuel tanks, lines, and carburetor (likely Linkert or similar era-specific).
Braking System:
Inspection, adjustment, and repair of drum brakes and associated linkages.
Suspension Components:
Service for front forks (likely springer or early hydraulic) and rear suspension (if applicable to specific models within Big Twin range).
Frame And Chassis:
Information on frame integrity, steering head bearings, and component mounting.
Body And Trim:
Details on fender mounting, tank installation, and basic trim component care.
Preventative Maintenance:
Regular service checks, lubrication points, and fluid changes.
Troubleshooting Guides:
Systematic approaches to diagnosing common mechanical and electrical faults.
Complete Engine Rebuild:
Disassembly, cleaning, inspection, measurement, and reassembly of all engine internal components.
Transmission Rebuild:
Detailed steps for gearbox overhaul, including gear inspection and bearing replacement.
Electrical System Repair:
Guidance on repairing or replacing wiring, switches, and basic electrical components.
Carburetor Adjustment And Rebuild:
Instructions for tuning and overhauling the primary fuel delivery system.
Brake System Maintenance:
Procedures for brake shoe replacement, adjustment, and drum inspection.
Suspension Service:
Fork oil changes, seal replacement, and steering head bearing service.
Wheel Bearing Service:
Inspection and lubrication/replacement of wheel bearings.
Tire Mounting And Balancing:
While often outsourced, basic guidance might be present.
Depth:
Comprehensive, suitable for experienced mechanics and dedicated restorers.
Diagnostic Level:
Advanced troubleshooting for mechanical and electrical systems of the era.
Rebuild Procedures:
Detailed, step-by-step overhaul instructions for major components.
Torque Specifications:
Likely includes critical torque values for engine and chassis fasteners.
Clearances And Tolerances:
Essential measurements for internal engine components and other wear parts.
Engine Type:
Air-cooled, OHV V-twin
Displacement Variants:
Primarily 45 cubic inch (740cc) WL series and 61 cubic inch (1000cc) U/UL series, with potential for later 74 cubic inch (1200cc) E/F/FL series within the broader Big Twin umbrella covering this period.
Bore Stroke 45Ci:
3.00" x 3.8125" (76.2 mm x 96.8 mm)
Bore Stroke 61Ci:
3.4375" x 4.125" (87.3 mm x 104.8 mm)
Compression Ratio:
Varies by model and year, typically around 5:1 to 7:1.
Horsepower:
Estimated 20-30 HP depending on displacement and tuning.
Torque:
Not typically stated in HP/TQ figures of modern terms; emphasis on low-end grunt.
Carburetor Type:
Primarily Linkert carburetors (e.g., M-series, DC-series) or Schebler for earlier models.
Fuel Type:
Gasoline (lead content expected for era-appropriate fuel, unleaded suitable with care).
Fuel Delivery:
Gravity feed from tank, sometimes with a fuel pump on later models or specific variants.
Oil Change:
Typically every 1,000 - 2,000 miles, or seasonally. Manual will specify.
Tune Up:
Regular checks of ignition timing, carburetor settings, and valve clearances recommended annually or every 3,000-5,000 miles.
Spark Plugs:
Check and clean/replace as needed during tune-ups. Manual will list appropriate types.
Engine Oil:
SAE 50 or SAE 60 motorcycle-specific oil (e.g., Harley-Davidson Genuine Motor Oil). Manual will provide precise grade.
Transmission Oil:
Gear oil, likely SAE 90 or 140. Manual will specify grade and capacity.
Primary Chain Case Oil:
Motorcycle specific oil, often the same as engine oil or a dedicated primary oil. Manual will confirm.
Fork Oil:
Specific weight hydraulic fork oil. Manual will specify weight and quantity.
Oil Leaks:
Common in older motorcycles due to aging seals and gaskets. Manual provides seal replacement procedures.
Carburetor Wear:
Linkert carburetors can develop wear in throttle shafts and jets, affecting idle and performance. Manual covers rebuilds.
Ignition Timing Drift:
Requires periodic checking and adjustment, especially with wear in the distributor or points. Manual details timing procedures.
Brake Performance:
Drum brakes require careful adjustment and maintenance for optimal, albeit limited, stopping power. Manual guides adjustments.
Valve Adjustment:
Requires periodic adjustment to maintain proper engine performance and longevity. Manual outlines the process.
Legacy:
Harley-Davidson has a long and storied history in motorcycle manufacturing, known for its V-twin engines and durable motorcycles.
Era Context:
This period represents a critical post-Depression and wartime era for Harley-Davidson, producing reliable machines for civilian and military use (e.g., WLA models).
Engine Development:
These Big Twins are evolutionary developments of earlier V-twin designs, focusing on reliability and increased power output.
Manufacturing Location:
Milwaukee, Wisconsin, USA.
Wartime Impact:
Significant production of military variants (WLA, XA) impacted civilian model development and availability during WWII.
