More mature models that keep the "lightweight feeling" in the 10th year of the 4-stroke YZ models Release of the six 2008 model Yamaha YZ series motocrossers

From July 17, 2007, Yamaha Motor Co., Ltd. (YMC) releases on the Japanese market the 2008 model 4-stroke motocrossers "YZ450F" and "YZ250F" mounting lightweight, compact liquid-cooled, 4-stroke DOHC single-cylinder engines on aluminum frames with further matured engine and frame features that made for even easier to use power development and greater race competitiveness. A special "YZ250F White Limited Edition" (50 units limit) with a smart white color scheme will be included in the release. The year 2008 marks the 10th anniversary of the launch of the first 4-stroke YZ series model, the YZ400F, in 1998. The new 2008 models of the "YZ250" and "YZ125," powered by liquid-cooled 2-stroke engines and famed for their proven light handling characteristics, will also be released with further maturation of features and performance beginning from August 1, 2007.
The 2008 versions of the entry level models "YZ85" and "YZ85LW" will be released from August 1, 2007, with new YZ series graphics.
The YZ series models can be purchased at dealerships officially authorized to handle Yamaha Off-road competition models in Japan.

Yamaha motocrosser YZ450F

Yamaha motocrosser YZ250

YZ450F/YZ250F on July 17, 2007
YZ250F White Limited Edition on Aug. 1, 2007
YZ250/YZ125 on Aug. 1, 2007
YZ85LW/YZ85 on Aug. 1, 2007

Deep Purplish Blue Solid E (blue)
Purplish White Solid 1 (white)(limited to 50 units)*
* YZ250F White Limited Edition only

In the spring of 1997, Yamaha overturned the status quo of the 2-stroke dominated motocross world by developing a 4-stroke motocrosser and entering it in competitions like the World Motocross Championships. This YZM400F factory machine ridden by A. Bartolini won a round of the WMX 500cc class at the Italian GP in April, and in May it won the Las Vegas round of the AMA Supercross series in the U.S. ridden by D. Henry. These high-profile victories were to signal the coming of a new era of 4-stroke motocrossers.

The production 4-stroke motocrosser YZ400F built around the 1997 factory machine technologies was released in 1998. Then in 2001, the 4-stroke YZ250F was released and quickly won a strong following of fans in Japan, Europe and North America. This led to the introduction of 4-stroke models by the other makers that have contributed to a big shift in the preference of riders over the past ten years, with the ratio of 4-stroke machines continuing to grow steadily. Within these trends, Yamaha has continued to develop both 2- and 4-stroke machines that make the most of the characteristics of the two engine types.

The lineup of new 2008 off-road models now being introduced includes technological improvements and further maturation for both the 2- and 4-stroke models. While maintaining the signature "lightweight feeling" of the existing Yamaha models, the new models feature improvements in power development characteristics, weight reduction and detailed improvements in rigidity tuning to put further polish on the famous Yamaha handling, such as outstanding front-end response during cornering at contributes to even greater competitiveness and riding comfort.

Engine

1) New port shapes and cam profile
To achieve a further improvement in combustion efficiency, the shapes of the intake ports have been optimized. This combines with the optimized cam profile to help improve torque character in the low- to mid-speed range. The new cam profile changes the intake valve timing and the overlap is changed also to create a good balance of intake and exhaust that improves torque character in the low- to mid-speed range.

2) Piston clearance and backlash* adjusted to help reduce mechanical noise
High-precision adjustments were made in the external diameter of the piston to optimize the clearance between the piston and the cylinder. This reduces piston (lateral) movement to a minimum and thus reduces vibration and mechanical noise. Also, adjustment of the backlash* of the primary gears enables another reduction in mechanical noise.
* Backlash is the gaps that exist in the meshing of the gears.

3) Other changes (shared features of the YZ450F and YZ250F)
Other changes include (1) a new finish for the crankcase cover and (2) a new muffler spec that clears the FIM noise regulation.

Chassis

1) New design for the steering stem assembly and main frame
In order to achieve a ride with a good feeling of rigidity while also reducing weight, the steering assembly has been re-designed. The frame's head pipe was shortened by 5 mm compared to the existing model, and to accommodate this the steering stem was also shortened by 5 mm. Furthermore, the shape of the forged aluminum under-bracket has been changed to an "H" cross-section shape to reduce weight and enable a further tuning of the rigidity balance. In connection with the above-mentioned changes, the rigidity balance of the aluminum frame's pivot assembly is optimized to achieve a better overall balance.
This increases the feeling of lightness to the handling, the ease with which the machine can be leaned into the curves and the feeling of lightness when entering a turn.
In the front assembly a lighter front fork protector and lighter brake parts are adopted to help achieve an even lighter handling feeling.

2) Improved front fork performance (shared feature of the YZ250F and YZ450F)
In addition to a change in the shape of the outer tubes of the front fork, further improvements have been made in the operability, damping characteristics and the comfort of the ride. Also, to achieve a good balance with the lightened front-end assembly, the rear suspension made of lightweight β titanium has been given new specifications. Revision of the shaft collar, adoption of lighter parts in the link assembly and optimizing the link ratio have all contributed to even better cushioning characteristics and traction characteristics.

3) Lightened front brake assembly
A new lightweight type front brake caliper has been adopted (same spec as 2007 model YZ250F). The diameter of the piston has been reduced from 27 mm to 22.65 mm and the shape and material used for the pads have been optimized. The diameter of the master cylinder piston has also been changed from the existing 11 mm to 9.52 mm . Furthermore, a lighter part is adopted for the wave type disc. And, changed the shape of the slotting holes from round to elongated types has helped reduce weight while improving braking force. New lightweight parts have also been adopted for the front axle and wheel collar. The combined effect of these changes creates an even lighter feeling while providing outstanding stopping power.

4) Wide type footrest adopted
A wide type stainless steel footrest proven popular on the WR450F has been adopted for additional comfort.

Engine

1) New-design piston enables high compression ratio setting of 13.5 : 1
A piston with a new top surface design has been adopted that enables an increase in the compression ratio from 12.5 : 1 to 13.5 : 1. This further brings out the inherent potential of the 5-valve combustion chamber design for excellent power development characteristics due to faster combustion. Also, in order to accommodate the higher compression ratio, changes have been made in the carburetor setting and the ignition timing has been optimized (new CDI unit adopted).

2) Optimized backlash reduces mechanical noise (same as 2008 model YZ450F)
As with the 2008 model YZ450F, adjustment of the backlash of primary gears and balancer gears achieved another reduction in mechanical noise by enabling better meshing of the gears.

3) Clutch assembly spec changed
The shapes of the boss clutch and the primary driven gear in the clutch assembly have been changed to promote better oil supply to the friction plates and clutch plates and contribute to better competitiveness at starts and coming out of turns.

Chassis

1) Lightened front assembly
In order to achieve a good balance of weight reduction and rigidity in the front assembly, (1) changes are made in the shape of the front fork outer tubes, (2) a lightweight front fork protector is adopted and (3) a new shaped (H cross-section) forged aluminum under-bracket is adopted. These changes further heighten the lightweight feeling that is the trademark of the YZ series models.

2) Other changes
Other changes include (1) a new brake pedal shape for reduced weight and better operability and (2) wide type stainless steel footrests for greater comfort (width increased compared to existing part from 45 mm to 55 mm on both sides). Also, a YZ250F White Limited Edition model with a cool and refreshing white color scheme has been prepared.

1) New-design reed valve spacer adopted (YZ125 only)
The flow of intake air from the carburetor through the manifold to the carbon reed valve is affected by the shape of the reed valve spacer. Improving the shape of the spacer on the 2008 model YZ125 has optimized flow volume and flow speed across the full rpm range from low to high rpm to improve acceleration performance.

2) All new front brake parts
To reduce weight in the wheel assemblies, the proven new brake system from the 4-stroke YZ series has been adopted. A lightweight front brake caliper has been adopted. The piston size is reduced and the shape and material of the pads has been optimized to achieve a further weight reduction. Also, the diameter of the master cylinder side piston has been reduced and a push rod structure is adopted and the lever shape optimized to improve the feeling of the lever touch. The result is a lightweight, compact brake system that provides outstanding function and operability.
A second measure aimed at reducing weight in the wheel assemblies is the adoption of lightweight wave-type disc rotors on the front and rear brakes. And, changing the shape of the slotting holes from round to elongated types has helped reduce weight while improving braking force.

3) New-design steering assembly
The same lightweight front fork protector that is used on the 2008 4-stroke YZ models is adopted. Lighter parts are also adopted for the front fork axle, the wheel collar and the axle bracket to increase the overall lightness of the machines' feeling.

4) Lightweight outer tubes for the front suspension
On the upside-down front fork (gas-liquid separation type) with 48mm diameter inner tubes, the outer tubes have been processed with a new method to reduce wall thickness and the spec of the inner tubes has been changed. The cushioning settings have also been optimized to maintain an ideal balance with the lightened front assembly. The settings of the rear suspension have also been optimized to achieve a good balance with the front suspension.

These models have a new look for 2008 by adopting YZ series graphics.