Segment:
Competition Motocross / Off-Road Performance Motorcycle
Competitors:
Honda CRF450R, Kawasaki KX450F, Suzuki RM-Z450, KTM 450 SX-F (though some models may overlap in year ranges)
Engine Type:
Liquid-cooled, four-stroke, DOHC, single-cylinder
Suspension Type:
High-performance motocross suspension (e.g., Kayaba USD forks, Monoshock rear)
Engine:
Top-end (cylinder head, valves, camshaft), Bottom-end (crankshaft, connecting rod, piston), Lubrication system, Cooling system (liquid-cooled), Fuel system (carburetor, fuel pump), Ignition system (CDI, spark plug), Exhaust system, Starting system (kick start)
Transmission:
Gearbox (transmission), Clutch (wet multi-plate), Shift mechanism, Gear ratios
Chassis:
Frame, Swingarm, Suspension (front forks, rear shock absorber), Steering system, Wheels, Tires, Brakes (front and rear disc brakes, hydraulic system)
Electrical:
Wiring harness, Lighting (headlight, taillight, brake light), Indicators, Battery, Charging system (alternator/stator, rectifier/regulator), Ignition coil, CDI unit
Maintenance:
Routine checks, Oil changes, Filter replacements, Chain adjustment, Spark plug service, Brake fluid replacement, Coolant replacement, Carburetor cleaning and adjustment, Valve clearance adjustment
Repair:
Engine disassembly and reassembly, Transmission overhaul, Clutch replacement, Suspension fork servicing, Shock absorber rebuilding, Brake system repair, Electrical component testing and replacement, Carburetor overhaul
Troubleshooting:
Diagnostic charts, Symptom-based troubleshooting guides, Common problem solutions
Depth:
Comprehensive from basic service to complete engine and gearbox rebuilds, including detailed torque specifications, measurements, and diagnostic procedures.
Engine Type:
Liquid-cooled, four-stroke, single-cylinder
Bore X Stroke:
95.0 mm x 63.0 mm (typical for 426cc)
Compression Ratio:
12.3:1 (typical, varies slightly by year)
Valve Train:
DOHC, 4 valves
Lubrication:
Wet sump with integrated oil cooler
Cooling System:
Liquid-cooled
Horsepower:
~50-55 HP (estimated at crankshaft)
Torque:
~30-35 lb-ft (estimated at crankshaft)
Carburetor:
Keihin FCR (Flat CR)
Carburetor Size:
39 mm (typical for FCR)
Fuel Type:
Unleaded gasoline (91 octane or higher recommended)
Ignition Type:
Digital CDI (Capacitor Discharge Ignition)
Spark Plug Type:
NGK CR9E or equivalent
Transmission Type:
5-speed manual constant mesh
Clutch Type:
Wet, multi-plate
Gear Ratios:
Specific ratios available in manual (e.g., 1st: 2.571, 2nd: 1.813, 3rd: 1.381, 4th: 1.130, 5th: 0.917)
Transmission Oil Type:
Yamalube 4 (or equivalent SAE 10W-30 API SG or higher motorcycle oil)
Transmission Oil Capacity:
Approx. 0.85 L (0.9 US qt)
Length:
Approx. 2175 mm (85.6 in)
Width:
Approx. 820 mm (32.3 in)
Height:
Approx. 1285 mm (50.6 in)
Wheelbase:
Approx. 1480 mm (58.3 in)
Ground Clearance:
Approx. 345 mm (13.6 in)
Dry Weight:
Approx. 106 kg (233.7 lbs)
Wet Weight:
Approx. 116 kg (255.7 lbs) (estimated with fluids)
Fuel Tank Capacity:
8.0 L (2.1 US gal)
Vehicle Type Safety Rating:
Not applicable (competition off-road vehicle)
Braking System:
Hydraulic dual disc front, Hydraulic single disc rear
Front Brake Spec:
250 mm disc
Rear Brake Spec:
245 mm disc
Frame Construction:
Semi-double cradle steel frame
Engine Oil Change:
Every 15-20 hours of riding or every 3 months
Oil Filter Replacement:
Every 2-3 oil changes or as needed
Air Filter Cleaning:
Every 5-10 hours of riding (more frequently in dusty conditions)
Spark Plug Inspection:
Every 20-25 hours of riding
Valve Clearance Check:
Every 20-25 hours of riding
Brake Fluid Replacement:
Every 12 months
Coolant Replacement:
Every 24 months
Engine Oil Specification:
Yamalube 4 (or equivalent SAE 10W-30 API SG or higher motorcycle oil)
Coolant Specification:
High-quality ethylene glycol-based antifreeze coolant (50/50 mix with distilled water)
Brake Fluid Specification:
DOT 4 hydraulic brake fluid
Common Wear Items:
Clutch plates, piston rings, valve guides, wheel bearings, swingarm bearings.
Carburetor Tuning:
Can be sensitive to altitude and temperature changes, requiring occasional re-jetting or adjustment for optimal performance.
Valve Adjustment Frequency:
Due to the high-performance nature, valve clearance checks are crucial to prevent potential damage.
Manufacturer:
Yamaha Motor Company
Yz Series Heritage:
The YZ series has a long and successful history in motocross, known for performance and innovation. The YZ400F introduction in 1998 marked Yamaha's entry into the four-stroke motocross market, evolving into the YZ426F for increased displacement and power.
Manufacturing Location:
Japan
Production Period:
2000-2002 (for this specific manual coverage)
Next Model Generation:
YZ450F (introduced in 2003)
Motorcycle Press Reviews:
Consistently reviewed as a powerful and competitive motocross machine, praised for its torque and suspension performance in its era. Received favorable comparisons against key rivals.
Racing Success:
The YZ426F platform was competitive in professional motocross and supercross racing during its production years.
