Positioning:
The Yamaha YZ450F was a dominant force in professional motocross and supercross during its era, known for its potent engine and advanced chassis. This manual caters to owners and mechanics seeking to maintain and repair this high-performance competition machine.
Competitors:
Honda CRF450R, Kawasaki KX450F, Suzuki RM-Z450, KTM 450 SX-F.
Vehicle Attributes:
Powerful 4-stroke engine, advanced suspension technology (e.g., KYB SSS forks), lightweight aluminum frame, aggressive styling, race-bred performance.
Engine:
Complete engine assembly, cylinder head, piston, crankshaft, connecting rod, lubrication system, cooling system, carburetor (Keihin FCR MX40 for most models in this range), ignition system.
Transmission:
Clutch operation, transmission gears, shifting mechanism, maintenance, and repair.
Drivetrain:
Final drive chain and sprockets, rear wheel hub, drive sprocket installation and removal.
Suspension:
Front fork (KYB SSS - Speed Sensitive System for later models, preceding versions), rear shock absorber (Monoshock), linkage system, adjustment procedures, service and rebuild.
Brakes:
Front and rear hydraulic disc brake systems, caliper maintenance, master cylinder service, brake fluid bleeding, pad replacement.
Electrical:
Ignition system components (CDI, stator, spark plug), lighting (if applicable, often minimal on competition bikes), wiring diagrams, troubleshooting electrical faults, battery maintenance (kickstart models).
Chassis And Bodywork:
Frame inspection and repair, fuel tank, seat, handlebars, footpegs, plastic body panels, fender replacement.
Wheels And Tires:
Spoke tensioning, wheel bearing maintenance, tire replacement, rim lock installation.
Routine Maintenance:
Oil changes, filter replacement (oil and air), chain lubrication and adjustment, spark plug inspection/replacement, valve clearance checks.
Disassembly And Assembly:
Complete teardown and reassembly of engine, transmission, suspension components, and chassis.
Troubleshooting:
Diagnostic guides for common performance issues, starting problems, electrical faults, and mechanical failures.
Rebuilds:
Detailed instructions for engine rebuilds (top end and bottom end), carburetor overhaul, and suspension rebuilds.
Adjustments:
Carburetor jetting, suspension settings, clutch and throttle cable adjustments.
Depth:
Comprehensive. Covers basic maintenance to full engine and component overhauls. Includes torque specifications, clearances, and diagnostic procedures.
Type:
4-Stroke, Liquid-Cooled, DOHC, 5-Valve, Single-Cylinder
Displacement:
449cc (approximately)
Bore X Stroke:
Variable depending on specific model year within the range, but typically around 95mm x 63.4mm.
Compression Ratio:
Typically around 12.3:1 to 12.5:1.
Horsepower:
Estimated 50+ HP at the crankshaft (factory figures vary, actual output depends on modifications and condition).
Torque:
Strong low-to-mid-range torque characteristic of this engine configuration.
Carburetor:
Keihin FCR MX40 (common for this generation), dual-throttle system on some later models.
Fuel Type:
Unleaded gasoline, minimum 91 octane (Octane Rating).
Oil Type:
SAE 10W-40 4-stroke motorcycle specific oil (e.g., Yamalube, Motul, Castrol).
Oil Capacity:
Approximately 0.8 to 1.1 liters (refer to manual for exact specification).
Type:
Liquid-cooled (radiators).
Coolant Type:
Permanent type antifreeze coolant (e.g., ethylene glycol based) with distilled water.
Type:
Constant-mesh 5-speed sequential gearbox.
Type:
N/A (Competition motorcycle, no factory automatic option).
Clutch:
Wet, multi-plate, cable-actuated.
Transmission Oil:
Engine oil is typically used for transmission lubrication as well. Refer to manual for specific type.
Length:
Variable, approximately 2175mm.
Width:
Variable, approximately 825mm.
Height:
Variable, approximately 1280mm.
Dry Weight:
Around 99-102 kg (218-225 lbs) depending on specific year and equipment.
Wet Weight:
Not typically specified, but includes fluids.
Fuel Capacity:
Approximately 8.0 liters (2.1 US gal).
Crash Test Ratings:
N/A (Competition motorcycle, not subject to road vehicle safety standards).
Braking System:
Hydraulic disc brakes front and rear for strong stopping power.
Suspension Performance:
Advanced suspension systems designed to absorb impacts and maintain control.
Frame Construction:
Durable aluminum alloy frame designed for rigidity and impact resistance.
Ergonomics:
Designed for rider control and comfort during aggressive riding.
System:
N/A (Pure competition off-road motorcycle, no infotainment features).
Features:
N/A (No electronic rider aids like traction control or ABS on these models).
Ignition:
Digital CDI (Capacitor Discharge Ignition) for precise spark timing.
Front Fork:
KYB Upside-Down (USD) forks with Speed Sensitive System (SSS) on later models, offering excellent damping and adjustability.
Rear Suspension:
Monoshock with adjustable spring preload, rebound, and compression damping.
Oil Change:
Every 10-15 hours of riding, or as recommended in the manual for severe use.
Air Filter Cleaning:
After every few rides, or more frequently in dusty conditions.
Chain Lubrication Adjustment:
Every ride, or as needed.
Valve Clearance Check:
Every 20-30 hours of riding, or as per manual recommendations.
Engine Oil:
SAE 10W-40, API SG or higher, JASO MA certified.
Brake Fluid:
DOT 4 hydraulic brake fluid.
Coolant:
50% ethylene glycol based coolant with distilled water.
Common Wear Items:
Clutch plates, piston rings, valve guides, wheel bearings, fork seals, chain and sprockets, spark plug, air filter.
Potential Failures:
Can include premature wear on the piston and rings if maintenance is neglected, potential carburetor jetting issues at different altitudes or temperatures, and fork seal leaks due to off-road abuse.
Oil Filter Example:
Yamaha Genuine Part # 5TA-13440-00-00 or equivalent aftermarket (e.g., K&N KN-145).
Air Filter Example:
Yamaha Genuine Part # 1S7-14451-00-00 or Twin Air # 157206.
