Articles specific to Yamaha.
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In 1997 the motorcycle industry was revolutionized when Yamaha unveiled its YZ400F. Here was a four-stroke competition motocross bike unveiled in Yamaha's YZ line when two-stroke bikes we thought to be the engine of choice. Historically, four-stroke engines were less responsive and housed in heavier machines than their two-stroke counterparts and just wouldn't do in a race world of tight turns and quick power. The nay-sayers were quickly quieted, however, when Doug Henery won the championship the first year it was raced.
Since the YZ400F roared onto the scene, Yamaha has pushed the four-stroke rev-limiter as is synonymous with the king of four-stroke motorcycles - even developing a four-stroke to win the 125cc class, the YZ250F. Yamaha YZs are laden with power, performance and handling - so much so that no competitor even attempted to challenge it for six years. Even free of competition, Yamaha continued to improve on their four-stroke technology. For 2003, not only did the YZ450F receive an extra 23ccs of power, but it also lost 13 pounds and received an all-new frame and handling updates making it an even better handling and easier starting machine. Now the third wave of four-stroke technology is being unleashed on the industry with the all-new YZ450F.
The YZ450F also gets an all-new, flatter fuel tank, seat radiator shrouds allowing more freedom of movement and weight transfer and more aggressive riding position and optimal rider movement. Whether jumping, going through whoops or cornering, handling is one of the most important elements of a race bike.
For 2003, Yamaha took the power and performance of last year's beloved YZ426F and added additional punch. The 449cc, liquid-cooled, four-stroke, patented titanium five-valve powerplant features an all-new four-speed transmission (down from five), reducing weight and increasing strength. The smooth shifting four-speed sheds a gear, but the revised gear ratios' efficient powerband delivery allows the bike to hit right out of a corner and pull hard down long straight-aways. Providing superior shifting, the highly acclaimed "three bar" shifting mechanism graces the tranny. Three shift fork guide bars are used to improve the power shift feeling when slamming the gears after a long straight or short shifting the bike out of turns. In addition, the YZ450F features the "works-style," adjustable clutch perch and lever (that can be adjusted at the starting gate with no tools), which makes for a lighter action and a superior feel, resulting in less rider fatigue.
Another common four-stroke characteristic that made the bike less user friendly in the past was difficulty starting when the engine was hot. The extra action of pulling in a compression lever and finding "top dead center" on the kick start meant riders may pass you before you were able to get the bike going again. Resolving this problem, the 2003 YZ450F features an all-new, convenient handlebar-mounted hot-start system and all-new automatic decompression system making starts a cinch.
Reducing weight on the first-class thumper, a newly designed exhaust pipe, now titanium verses steel; redesigned air filter case and oil pump; smaller cylinder head and all-new crankshaft. And, adding convenience to that low weight, the oil filter can be easily removed without removing the exhaust pipe making routine maintenance painless.
Flying 100 feet through the air, the rider feels weightless, but what goes up must come down, so thankfully the YZ450F suspension ensures a smooth landing with 11.8 inches of travel up front and 12.4 inches in the rear. An all-new tapered swingarm in the rear reduces weight and increasing rigidity for a more compliant rear suspension. Coupled with fully adjustable rear shock's hi/lo-speed compression adjuster and refinements including a new linking ratio and enhanced damping, the YZ's rear suspension is the choice set-up on a race-bread machine. The front suspension received recalibrated fork settings delivering improved damping force with less bottoming for a smoother overall ride.
For 2003, braking is improved yet again for improved delivery and feel with all-new light-weight front and rear master cylinders and calipers, combined with a 250mm floating disc brake up front and 245mm rear disc.
Again for 2003, Excel rims grace the YZ450F in the front and rear, providing superb strength throughout the season. A light chain coupled with Yamaha's lightweight hub, aluminum spoke nipples and Dunlop 739FAs complete one of the most aggressive rear setups on a production machine today.
The 2002 YZ450F will be available in Team Yamaha Blue/White at a manufacturer's suggested retail price of $6,299 USD.
Type: 449cc, 5-valve (titanium) liquid-cooled, DOHC, four-stroke
Bore & Stroke: 95 x 63.4mm
Compression ratio: 12.5:1
Carburetor: 39mm Keihin FCR flat-slide w/throttle position sensor
Carb Jetting: #165 Main / #100 Pilot Air / #42 Pilot Jet
Type: Constant mesh 4-speed, multi-disc wet clutch
Gearing: 62 / 22 (2.818)
Frame: Semi-double cradle
Front suspension: 46mm Kayaba inverted telescopic fork, 11.81" travel; adj. compression & rebound
Rear suspension: Fully adjustable Kayaba shock, 12.4" travel; separate Hi/Lo compression adjustments
Rake / Trail: 27.2° / 4.65"
Front brake: 250mm floating disc
Rear brake: 245mm disc
Front tire size: 80/100-21 Dunlop 739
Rear tire size: 100/90-19 Dunlop 739
Fuel tank: 1.8 gallons
Dimension and Dry Mass
Overall length: 85.5"
Overall width: 32.6"
Overall height: 51.3"
Ground clearance: 14.6"
Seat height: 39.2"
Dry mass: 222 lbs.
- Extra 23cc engine, lost 13lbs and received new frame and handling updates.
- All-new, flatter fuel tank, seat radiator shrouds.
- All-new 4-speed transmission (prev. 5), reduced weight and increased strength.
- All-new convenient bar-mounted hot-start system and all-new automatic decompression system.
- Newly designed exhaust pipe, now titanium verses steel.
- Redesigned air filter case.
- Redesigned oil pump.
- Smaller cylinder head.
- All-new crankshaft.
- All-new tapered swingarm in the rear reduces weight and increasing rigidity for a more compliant rear suspension.
- New rear suspension linking ratio and enhanced damping.
- Recalibrated fork settings.
- All-new light-weight front and rear master cylinders and calipers, combined with a 250mm floating disc brake up front and 245mm rear disc.
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