2002 Yamaha YZ426F
General Specifications
| Model | Yamaha YZ426F |
| Year | 2002 |
| Category | Motocross |
| Engine Type | Liquid-cooled, four-stroke, single-cylinder, DOHC, 5-valve |
| Weight | Approximately 113 kg (249 lb) dry |
Engine
| Displacement | 426 cc |
| Bore x Stroke | 95.0 x 60.1 mm |
| Compression Ratio | 12.5:1 |
| Fuel System | Keihin FCR 39 mm flat-slide carburettor with accelerator pump | Replacement Options |
| Ignition | CDI |
| Spark Plug | NGK CR8E |
| Spark Plug Gap | 0.7-0.8 mm (0.028-0.031 in) |
| Cooling System | Liquid cooled |
| Starting System | Kick start with manual decompression system |
Transmission
| Transmission | 5-speed constant-mesh |
| Clutch | Wet multi-plate |
| Final Drive | Chain |
Dimensions
| Overall Length | 2,181 mm (85.9 in) |
| Overall Width | 827 mm (32.6 in) |
| Overall Height | 1,303 mm (51.3 in) |
| Wheelbase | 1,481 mm (58.3 in) |
| Ground Clearance | 381 mm (15.0 in) |
| Seat Height | 998 mm (39.3 in) |
| Fuel Capacity | 8.0 litres (2.1 US gal) |
Chassis
Suspension
| Front Suspension | 46 mm KYB inverted telescopic fork with adjustable compression and rebound damping | Fork Oil Levels |
| Front Suspension Travel | 300 mm (11.8 in) |
| Rear Suspension | KYB Monocross single shock with piggyback reservoir, adjustable spring preload, compression and rebound damping |
| Rear Suspension Travel | 315 mm (12.4 in) |
| Fork Oil | Yamaha Suspension Oil 01 or equivalent; oil level 135 mm (5.31 in) from top of fully compressed outer tube with spring removed, adjustable within the specified service range |
Brakes & Wheels
| Front Brake | Hydraulic single disc, 250 mm |
| Rear Brake | Hydraulic single disc, 245 mm |
| Front Wheel Size | 21 in |
| Rear Wheel Size | 19 in |
Service Data
| Fuel Type | Premium unleaded petrol |
| Premix Information | Not applicable - four-stroke engine |
| Gearbox Oil | Engine and transmission share the same dry-sump oil supply; SAE 10W-30 or 10W-40 four-stroke motorcycle oil meeting Yamaha specification; approximately 1.5 L after draining, 1.6 L with oil filter replacement and 1.7 L after engine disassembly |
| Air Filter | Oiled polyurethane foam element |
| Service Notes | Dry-sump lubrication with engine oil stored in the frame reservoir. Check oil level using the specified warm-engine procedure. Valve clearance: intake 0.10-0.15 mm; exhaust 0.20-0.25 mm. Manual decompression lever and correct starting procedure are important on the original 2002 model. |
2002 Yamaha YZ426F - The Final Evolution of Yamaha's 426
The 2002 Yamaha YZ426F was an evolutionary update rather than an all-new model. By this point Yamaha had several years of experience with its revolutionary four-stroke motocross platform, beginning with the YZ400F and developing into the larger YZ426F for 2000. The 2002 machine represented the final year of the YZ426F before Yamaha replaced it with the lighter YZ450F for 2003.
Its 426 cc liquid-cooled DOHC five-valve engine retained the 95.0 x 60.1 mm bore and stroke and 12.5:1 compression ratio. A Keihin FCR flat-slide carburettor supplied the fuel, and correct jetting and accelerator-pump operation remain important to starting and throttle response today. Owners dealing with an ageing original unit can consult the MXOwners carburettor replacement and reference information.
The 2002 YZ426F also retained the manual decompression starting system for which these early Yamaha four-strokes became famous. Correct technique makes a substantial difference: bring the engine to compression, use the decompression lever to move the piston slightly beyond top dead centre, return the kickstarter and then kick firmly. Later Yamaha four-strokes would make this process considerably easier with automatic decompression.
The steel-framed chassis used 46 mm KYB inverted forks with approximately 300 mm of travel and a KYB Monocross rear suspension system providing approximately 315 mm. Owners servicing an original front end can use the MXOwners fork oil levels and suspension reference. Original tyre sizing remained the familiar motocross combination of 80/100-21 front and 110/90-19 rear, with the MXOwners motocross tyre size guide useful when comparing modern replacements.
For owners today, the 2002 YZ426F is significant because it represents the mature version of Yamaha's pioneering 426 platform. Its steel frame, carburetted engine, manual decompression lever and substantial four-stroke power give it a distinctly early-generation character. Regular oil and filter servicing, correct valve clearances, a clean air filter and careful inspection of chassis and suspension bearings remain essential. As the last YZ426F before the arrival of the YZ450F, the 2002 model occupies an important place in the transition from the pioneering YZ400F era to the modern 450 four-stroke motocross class.
