With new-design lightweight aluminum frame and titanium spring for boosted performance Release of the 2006 model Yamaha 4-stroke motocrossers "YZ450F" and "YZ250F"

Yamaha Motor Co., Ltd. (YMC) announces the coming release of the highly competitive and further matured 2006 model 4-stroke motocrossers "YZ450F" and "YZ250F" mounting liquid-cooled, 4-stroke DOHC single cylinder 5-valve compact engines on newly designed lightweight aluminum frames featuring the first rear suspension with titanium springs ever on production motorcycles. The "YZ250F" will be released on Japanese market on September 20, 2005 and the "YZ450F" on November 25, 2005.

Yamaha Motocrosser "YZ450F"

YZ450F November 25, 2005
YZ250F September 20, 2005

Deep Purplish Blue Solid E (Blue)

The 2006 models YZ450F and YZ250F have been designed under the theme of "Number one 4-stroke motocrossers in competitiveness and quality."Both models feature improvements to improve the maturity of the engines while also adopting newly designed lightweight aluminum frames. Competitiveness has also been boosted with the addition of new features like rear suspensions with lightweight titanium springs.
Improvements to the engine of the 2006 model YZ450F include (1) a new engine character that is powerful but easy to use, (2) change to a 5-speed transmission (from a 4-speed) to expand range of use and (3) improved feeling. As for the chassis, various new technologies have been adopted throughout the design to (1) provide greater ease of handling when entering a curve, (2) improve stability at higher speeds and (3) achieve an even lighter weight feeling.
The YZ250F has also been given improvement to increase engine maturity while adopting the same chassis spec changes as the YZ450F to improve competitiveness and exterior quality.

- YZ450F Engine

1) New dry sump oil system contributes to concentration of mass
A newly adopted dry sump type lubrication system featuring an oil tank in the crankcase has been adopted to achieve excellent lubrication qualities, while also contributing to a better concentration of machine mass. The design is simpler because it eliminates the need for the piping required in the existing system that used the down-tube as the oil tank. This improved concentration of machine mass combines with the new frame design and the optimized dimensions to contribute to lighter steering feeling and greater freedom of lines that can be taken through turns.
Furthermore, a piston cooling system that directs a pinpoint flow of engine oil to the desired portion of the cylinder outside the piston area has been adopted to ensure outstanding reliability. Also, the oil passage that carries the lubricating oil to the cylinder head has been directed through the cylinder wall for a further boost in reliability.

2) Optimized cylinder forward incline angle
To get an excellent chassis balance with better concentration of weight mass, the forward incline of the engine cylinder has been raised slightly and at the same time bring the center of gravity of the machine closer to the rider. In combination with the new frame and new dimension settings, this helps achieve an optimum overall body weight balance.

3) New-design intake system
A newly designed air cleaner box has been adopted along with a new-design air cleaner joint to accommodate the new engine design. The side cover duct has also been redesigned to accommodate these changes and further contribute to outstanding intake efficiency.
The FCR-MX39 carburetor, featuring an acceleration pump known for very linear response, has been given new settings to best accommodate the new intake system. Furthermore, the intake port shape has been optimized to accommodate the new cylinder incline angle.

4) Optimized balancer weight for ideal balance with primary inertial force
To reduce vibration and bring out easy-to-use power development, a new-design 50% balancer has been adopted. Usually, to reduce the vibration felt from a single cylinder engine due to the reciprocating motion of the piston and connecting rod, a balancer is positioned on a shaft diagonally above the crankshaft and rotated in the opposite direction to cancel out the engine's inertial force. On the existing YZ450F model, however, a balancer of somewhat less than the 50% balancer that would theoretically cancel out the engine vibration efficiently was adopted in order to achieve a desirable balance of drivability and vibration. On the 2006 YZ450F, however, it was possible to adopt an exactly 50% compact balancer thanks to improvements like a new-design high-strength conrod and piston, high-density balancer weight and the optimized inertial mass of the crankshaft. This made it possible to achieve both the outstanding power feeling a 450cc engine should have plus low vibration. This contributes to greater ease of use. Also, the balancer shaft gear is one with larger teeth to reduce mechanical noise.

5) New-design lightweight radiator adopted
A compact new radiator design has been achieved by revising the dimensions in width, height and depth. At the same time, optimization of the air induction fin promotes a better flow of air to the radiator when running to achieve the same cooling effect as the existing model while reducing the weight of the unit. This also contributes to a lighter feeling to the steering assembly.

6) Newly designed exhaust pipe and muffler
To accommodate the new incline angle of the engine while at the same time contributing to better concentration of mass, a new muffler layout has been adopted. At the same time, the spec has been changed to meet new race regulations. Also, an expansion chamber called a "pre-chamber" has been added to the exhaust pipe to achieve a smoother and deeper power development character.

7) 5-speed transmission adopted
In order to accommodate a wide range of uses from closed-course competition to open-area desert races, a 5-speed transmission capable of adapting to changing race conditions has been newly adopted. This ensures a ride with potential for even smoother application of drive force.

8) New CDI unit
In order to best accommodate the new engine character, a new CDI unit with revised ignition advance characteristics has been adopted. This contributes to smoother drivability.


- YZ250F Engine

1) Exhaust system design changes making even better use of exhaust pulse
In order to achieve good throttle response and even better power development characteristics in the low- to mid-speed rpm range, the exhaust system specifications have been revised. To increase the breadth of the exhaust pressure pulse, the existing 2-stage expansion format was changed to a 4-stage type. This resulted in a further improvement in filling efficiency induced by the exhaust pulse effect, thus contributing to better power development characteristics. Also, to accommodate the new exhaust system spec, the settings of the FCR37 carburetor have been changed along with the CDI unit's advance characteristics.
To accommodate the exhaust system spec change (4-stage expansion) and the new frame structure, the course of the exhaust pipe and diffuser pipe have been changed as well. Also, the size of the outside tube of the silencer has been changed to meet new race regulations.

2) New dry sump type system with separate oil tank
A new dry sump type lubrication system with a separate oil tank positioned in front of the engine has been adopted to lower center of gravity. This has been accompanied by a change in the shape of the strainer chamber in the crankcase that improves the oil circulation route. The new strainer chamber shape has increased the crankcase capacity and reduces oil churning resistance, which in turn reduces pumping loss. Meanwhile, the piping to the oil tank and the crankcase fastening bolt design have also been changed.

3) Large-capacity radiator adopted
A new-design radiator of the same size as the YZ450F has been adopted. The new unit provides greater cooling effect than the radiator on the existing model for improved reliability.

4) Other changes
Other changes to accommodate the new aluminum frame include (1) the mounting position of the TPS (Throttle Position Sensor) unit, (2) a more compact cold starter knob shape and (3) a new kick crank shape.

1) New-design lightweight aluminum semi-double cradle frame adopted
To achieve outstanding handling performance for even greater competitiveness, a new-design lightweight aluminum semi-double cradle type frame has been adopted. The upper and lower large portions of the aluminum frame are formed of forged pieces in a structure that sandwiches the cast parts. This new frame (for both the YZ450F and YZ250F) is made up of nine parts made of four different kinds of aluminum (cast parts, forged parts, pipe stock and extruded aluminum) used selectively in accordance with the type of strength needed in each part of the frame and welded together into units with advanced welding techniques to achieve not only the desired strength and rigidity balance while maintaining right amount of "forgiveness" but also an attractive exterior appearance of functional beauty.
Compared to the 2005 2-stroke model YZ250 aluminum frame, this new frame is about the same in terms of rigidity in the vertical direction and more rigid in the lateral direction and with regard to torsion in order to achieve a character that best fits the drive force characteristics of a 4-stroke. This frame has a number of merits including offering added handling motion stability as well as greater straight-line stability, reduced rider fatigue, chassis stability during braking and light handling.

2) Rear suspension with first titanium spring on a production motorcycle
The rear suspension is a new beta type titanium spring with greater fatigue strength and tenacity. With an original two-phase heat processing performed before and after the coil is formed, it is given outstanding strength and fatigue tolerance. Compared to the present steel spring, the new spring itself is 500 g lighter, which contributes to a reduction in unsprung weight for boosted suspension performance.
Also, the diameter of the damper rod has been increased from 16 to 18 mm and the amount of oil displacement increased to improve the cushioning characteristics, especially in the low speed range. Furthermore, the combined balance of 30% increase in the gas chamber capacity to ensure more stable performance and the reduced friction achieved with the new Kashima coating (previously Alemite), help bring out excellent performance.

3) New-design rear arm
This new arm is made by the "hydroforming" technique that has been used since 2002. This manufacturing method shapes the aluminum stock by applying pressure to the inside in a way that creates a smoother and more precise form. The new rear arm helps achieve excellent chassis balance thanks to a re-evaluation of the right and left balance of the cast aluminum parts around the pivot and increased lateral rigidity. (New-design rear arm is the same as the 2006 2-stroke YZ250/YZ125 models.)

4) Revised dimensions for lower machine height
With the adoption of the new frame, the dimensions have also been revised. The result is better concentration of mass and a lower machine height. The lower machine height contributes to a sense of compactness that makes the machine easier for the rider to handle.

5) Upside-down type front fork with optimized internal structure
The air-oil separation type upside-down front fork with 48 mm diameter inner tubes, which provides more stable performance by preventing air from entering the cartridge chamber, has been improved by (1) revising the strength balance between the outer and inner tubes, (2) use of Kashima coating on the pressure tank, (3) use of a polished Kashima coating on the piston rod to reduce friction, (4) revised cylinder diameter (25mm → 24mm) improved primary cushioning character, (5) adoption of a low-friction oil seal and (6) revision of the secondary cushioning force generating system.
The inner tubes continue to feature a TCV (Transfer Control Valve) that optimizes cushioning by functioning when the cylinder approaches bottom and begins to enter the taper piece at the end of the inner tube. The combined effect of these improvements produces outstanding cushioning characteristics.

6) Front assembly with optimized rigidity balance
The cast aluminum handle crown features greater rigidity in the vertical direction and with regard to torsion compared to the existing part. Meanwhile, the forged aluminum under-bracket has about the same rigidity as the existing unit in the lateral direction and increased rigidity in the vertical direction and with regard to torsion of between 10 and 20%. The combined effect of these changes is outstanding chassis balance.

7) Adoption of tapered aluminum handlebar with adjustable position, plus new seat material
The new aluminum handlebar has a Pro Taper spec and is lighter than the one on the existing model. Also the handle crown and handle mount bracket have been designed separately and given an offset in relation to the center axis. This has made it possible to include a two-step handlebar position adjustment capability in the front-rear direction by changing the front-rear alignment of the bracket.
In addition, a new seat cushion material has been adopted for greater comfort. The material is characterized by softness in the initial contact and increasingly firm body hold as deeper pressure is applied. Also, to bring out the full effect of this new material, the depth of the cushioning has been increased in comparison to the existing model. The contact portion of the seat has been finished in a flatter shape without mounding for a quality appearance and greater riding comfort.

8) Other features like new brake and exterior parts
Other new features include a new rear brake caliper, a new rear brake pad material and a new-design caliper protector and new-design disc cover. Furthermore, exterior parts including the number plate and newly designed parts for the front fender to give a fresh new look to the body styling that speaks of a next generation machine. (All these specs are the same as the 2006 2-stroke YZ250/YZ125 models.)