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Henry Ford once said you can get one of his cars in any color you want, as long as it’s black.
Take a look at the impressive line of Yamaha dirt bikes, and the only thing they have in common is that they’re all blue, with white and black trim.
The tuning fork company offers everything from minis to their top-of-the-line YZ four stroke racer. Let’s take a look at the four stroke that changed racing first, and then check out the rest of the line.
On June 23rd, 1997, Yamaha’s revolutionary YZ400F four-stroke opened an entirely new world of motocross. The 400F joined the YZ family as a purpose built four-stroke competition motocross bike and the results were stunning. Dealers couldn. t keep the bike on the showroom floors as racers such as Doug Henry, Jimmy Button, and Doug Dubach demonstrated to the world the bike. s capabilities including the 1998 Outdoor Motocross National Championship Title.
In 1997, Yamaha engineers initially began to build the YZ400F with a goal of exceeding all current production four-strokes. The end result produced a four-stroke that was not only capable of beating current four-strokes, but a machine with the ability to run head-to-head on a motocross track with production two-stroke 250cc bikes.
The Yamaha four-stroke is similar to the YZ125 and YZ250 with brakes, suspension, frame geometry and ergonomics paralleling the two-strokes currently in Yamaha’s line-up.
For 2000, Yamaha again improved on the machine that took the motocross world by storm. The newest call letters for the popular four-stroke are YZ426F. The most recognizable change for 2000 is the increase of the powerplant from 400cc to 426ccs. Though immediate competition is not yet in sight, Yamaha wanted to cement consumer belief that the new-generation YZ426F is the best motocross four-stroke on the planet, improving the power, handling, suspension and adding (add by subtraction) lighter components.
The YZ426F features a single shaft balancer, dry sump lubrication, and a kick start with a manual decompressor at a dry weight of 231 pounds. The 426cc DOHC motor utilizes a five-valve head that produces direct power to the dirt. The smooth, tractable four-stoke minimizes wheelspin and allows the rider to accelerate quicker out of dry turns than a 250cc two-stroke.
In the power department, a highly modified bigger-bore engine now displaces 426cc. This has been achieved by increasing the bore from 92mm diameter to 95mm, while the short 60.1mm stroke remains unchanged. A 19mm diameter piston pin, 1mm larger than the ‘99 design, as well as a modified connecting rod and a beefed-up big end bearing, widened 1mm to 16.8mm, accommodate the increased bore changes.
A larger diameter silencer (50.8) and a modified CDI with a decreased diameter rotor, 98mm to 83mm, improve the throttle response of the larger motor. The net result is an engine that delivers more low to mid-range power, while at the same time retaining its free-revving character.
Less weight and improved power translates into more speed. Minor engine braking, coupled with powerful front and rear disc brakes, allow 426F pilots to charge aggressively down the straights and feel confident in the stopping power.
A new Keihin FCR, with throttle position sensor (TPS) carburetor is designed to offer even better throttle response in a variety of conditions. The carburetor now sits more vertical and features an integrated red-colored hot start. Additionally, the intake now features a light resin joint between the carburetor and the air box to replace the previous aluminum component.
To handle the YZ426F. s increased low to mid range torque output, a new heavy-duty clutch was added. The friction plates diameter is increased from 148mm to 155mm and the number of plates is increased from 7 to 8. Larger plates equal a larger right-side engine case; the diameter is now increased to 157mm.
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| Larger Radiators on the 2000 YZ426F |
Attention was paid to the cooling system on the new big-bore engine, and the YZ426F’s increased power will be matched by the placement of new larger-capacity radiators. Supplied in bare, unpainted aluminum, the radiators are 10mm wider and incorporate 11 core tubes each, one more than the ‘99 model, keeping the heat to a minimum.
The YZ426F engineers also succeeded in creating an even more agile handling package, compliments of a new triple clamp, improved forks and shock, and a high-tensile steel frame. To increase front-end rigidity for precision steering, the thickness of the lower clamp where it grips the fork tube, has been increased by 5mm and the underside of the lower triple clamp now features and extra strengthening rib.
Also modified is the upper triple clamp, where the handlebar mounting brackets have been shifted forwards by 10mm. a move that enables the rider to be placed in a more aggressive riding position. The forks are now outfitted with lightweight aluminum piston rods, replacing steel, for smoother overall suspension action. New anti-stiction dust seals are fitted and the internal faces of the outer tubes have a new low friction treatment. A new aluminum damper rod replaces last year. s steel component in the rear suspension.
An all-new compression damping adjuster features high and low speeds, to allow the rider to fine-tune his machine to meet the ever-changing track conditions.
The frame is manufactured from stronger HT-780 steel tubing utilizing new brazing technology in its construction, to create a lighter and more rigid assembly. The head pipe is moved back 5mm, giving the 426F a very compact 58.7″ wheelbase. Switching from steel to aluminum on the subframe resulted in further weight savings.
Continuing its racing attitude, the YZ426F is loaded with components that previously were expensive aftermarket items, highlighted by a radically new “works-style” adjustable clutch perch and lever. Excel rims, an industry icon, grace both the front and rear tires and a lightweight hub provides increased reliability and offers less unsprung weight on the track.
The YZ426F will be available in Team Yamaha Blue/White and the manufacturer’s suggested retail price is $5,899
