Yamaha release 2008 YZF range

Image Yamaha Motor Australia has released the latest incarnations of the four-stroke motocross bikes that invented a category, the race winning YZFs.

 

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2008 YZ450F

Yamaha Motor Australia has released the latest incarnations of the four-stroke motocross bikes that invented a category, the race winning YZFs. The 2008 models come with significant improvements aimed at keeping the class leaders at the top of the podium, as demonstrated by YZ450F World MX Series leader Josh Coppins and YZ250F World MX Series leader Antonio Cairoli.

Both models come in two guises, standard Yamaha Racing Blue/White and Special Edition White/Red. YZ450F, the undisputed MX1 class leader With Josh Coppins leading the ’07 MX1 series – and the bike’s unrivalled track record from ’06 that includes winning 27 out of 30 heats – the YZ450F is officially today’s most successful MX1 machine.

 

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New Red and White colour scheme

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For 2008 season the undisputed class leader’s engine gets a number of significant improvements – including reshaped intake ports and cam profiles, reduced piston tolerance and modified transmission backlash and shorty muffler. And the YZ450F’s lightweight aluminium chassis runs with a shorter headpipe, lighter forks, compact new front caliper, and modified rear suspension – which makes the 2008 bike accelerate better, turn quicker and feel lighter, for an even more dominant package.

YZ450F engine

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The engine of the 2008 model maintains the outstanding characteristics of the existing five valve powerplant while achieving further improvements in power output character and reliability. This has been done by improving combustion efficiency by optimising the shapes of the intake ports and cam profiles. In addition, the intake valve timing and overlap is changed to create a good balance of intake and exhaust.

All of these changes help improve torque character in the low- to mid-speed range. Micron-level adjustments have been made to the external diameter of the piston to optimise the clearance between the piston and the cylinder. This reduces piston (lateral) movement to a minimum and thus reduces vibration and mechanical noise. Adjustment of the backlash of primary gears (in the clutch assembly) and balancer gear further reduces mechanical noise by enabling better meshing of the gears.

The engine breathes via a new larger-diameter titanium exhaust pipe and super compact muffler that saves weight and improves balance. Adjusting the shape of the exhaust pipe taper helps achieve excellent exhaust efficiency. The tapered silencing element known as a “punched cone” is used for the first time ever on a production motocrosser. This has enabled around a 35% reduction in the length of the muffler (505 mm to 333 mm) and a 270g weight reduction.

YZ450F chassis

To further develop the lightweight feel that is the trademark of the YZ models, detail changes have been made throughout the chassis design. As a result, the new model is even lighter handling and exhibits outstanding front end response during cornering plus greater riding comfort. In order to achieve excellent rigidity while also reducing weight, the steering assembly has been re-designed.

The frame’s head pipe is now 5mm shorter compared to the existing model, and to accommodate this, the steering stem is also 5mm shorter. The shape of the forged aluminium under-bracket has been changed (to an “H” cross-section shape) to reduce weight and enable a further tuning of the rigidity balance. The rigidity balance of the aluminium frame’s pivot assembly is also changed to improve overall balance. This ‘lightens’ the handling, or the ease with which the machine can be leaned into a turn.

In the front assembly a lighter front fork protector (120g lighter than the existing part) is adopted. This combines with the lighter brake parts to achieve an excellent rigidity balance in the front end. In addition to a change in the shape of the outer tubes of the front fork, further improvements have been made in the damping characteristics and the comfort of the ride on both YZF models.

And in order to achieve a further reduction of front assembly weight and good balance, a lightweight titanium spring has been adopted in the rear suspension. The shaft and collar have been re-designed and the peripheral parts lightened. At the same time the link ratio has been optimised to achieve excellent cushioning characteristics and bring out optimum traction performance.

Image A new lightweight type (less 220g) front brake caliper has been adopted. The diameter of the piston has been reduced from 27mm to 22.65mm and the shape and material used for the pads have been optimised. The diameter of the master cylinder piston has also been changed from the existing 11mm to 9.52mm (less 45g). Furthermore, a lighter wave type disc is adopted with new elongated slotting holes to help reduce weight while improving braking force.

New lightweight parts have also been adopted for the front axle and wheel collar (less 47g). The combined effect of these changes creates an even lighter feeling while providing outstanding stopping power. The rear brake retains the existing spec.

To provide even better traction characteristics, a wide 120/80-19 (D756) size tyre is adopted for the rear wheel (compared to the existing model’s 110/90-19/D756). The front tyre has also been changed from a D739FAL to a D742FA.

And to increase riding comfort, the wide type stainless steel footrests proven popular on the WR450F have been adopted (the existing footrests were titanium).

YZ250F

 

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2008 YZ250F

Tony Cairoli’s phenomenal record in the 2007 MX2 series underlines the YZ250F’s awesome unbeatable potential. Running a higher 13.5:1 compression ratio, and offering lower reciprocating weight and reduced frictional losses, this 2008 model GPdeveloped engine allows the highrevs to run even harder and faster. And to handle the extra performance we’ve fitted an uprated clutch with an increased oil supply.

New lightweight forks deliver quicker turning – and a revised linkage and new shock settings ensure superior handling and even quicker lap times.

YZ250F engine

As with the YZ450F, the engine of the 2008 model YZ250F maintains the outstanding characteristics of the existing model with additional refinements to engine character and reliability. 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 five-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 to the carburettor setting and the ignition timing has been optimised (and new CDI unit adopted). Meanwhile, adjustment of the backlash of primary gears (in the clutch assembly) and balancer gear reduces mechanical noise by enabling better meshing. The shapes of the boss clutch and the primary assembly have been changed to promote better oil supply to the friction plate(s) and clutch plate(s) and contribute to better competitiveness at starts and coming out of turns.

YZ250F chassis

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Weight reduction measures have been taken in order to lighten the handling of the controlled flex chassis. Changes have been made in the shape of the front fork outer tubes, a lightweight front fork protector is adopted (less 120 g compared to existing part) and a new shaped (H cross-section) forged aluminium under-bracket is adopted.

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As per the YZ450F, the front fork performance and rear suspension link ratio have been optimised and a new titanium spring employed (these are shared features of YZ250F and YZ450F). Other changes include a new brake pedal shape to reduce weight and the same YZ450F wide type stainless steel footrests are used for greater comfort (width increased compared to existing part from 45 mm to 55 mm on both sides). To match these chassis changes, Bridgestone tyres are fitted (front: M403, rear: M404) where previous models have used Dunlops.

2008 YZ450F SPECIFICATIONS
Engine type Liquid-cooled, 4-stroke, DOHC, 5 titanium valves, forward-inclined single cylinder Displacement 449 cc
Bore x stroke 95.0 x 63.4 mm
Compression ratio 12.3 : 1
Lubrication system Dry sump
Fuel System Keihin FCR-MX39/1
Clutch type Wet, multiple-disc
Ignition system CDI
Starter system Kick
Transmission system Constant mesh, 5 speed
Final transmission Chain
Fuel tank capacity 7 litres
Oil tank capacity 1.2 litre
Chassis: Semi-double cradle
Front suspension Telescopic forks
Front travel 300 mm
Rear suspension Swingarm (link suspension)
Rear travel 313 mm
Front brake Single disc, Ø 250 mm
Rear brake Single disc, Ø 245 mm
Front tyre Dunlop 80/100-21 51M
Rear tyre Dunlop 120/80-19 62M
Length 2195 mm
Width 825 mm
Height 1306 mm
Seat height 1001 mm
Wheelbase 1495 mm
Min ground clearance 375 mm
Dry weight 99.5 kg
Warranty Three months, parts only
RRP (inc GST) $11,499 and $11,599 for Special Edition White/Red model

 

2008 YZ250F SPECIFICATIONS
Engine type Liquid-cooled, 4-stroke, DOHC, 5-valve, forward-inclined single cylinder
Displacement 250 cc
Bore x stroke 77.0 x 53.6 mm
Compression ratio 13.5 : 1
Lubrication system Dry sump
Fuel System Keihin FCR-MX37/1
Clutch type Wet, multiple-disc
Ignition system CDI
Starter system Kick
Transmission system Constant mesh, 5-speed
Final drive Chain
Fuel tank capacity 7 litres
Oil tank capacity 1.3 litre
Chassis: Semi-double cradle
Front suspension Telescopic forks
Front travel 300 mm
Rear suspension Swingarm (link suspension)
Rear travel 307 mm
Front brake Single disc, Ø 250 mm
Rear brake Single disc, Ø 245 mm
Front tyre Bridgestone 80/100-21-51M
Rear tyre Bridgestone 100/90-19 57M
Length 2166 mm
Width 825 mm
Height 1300 mm
Seat height 997 mm
Wheelbase 1469 mm
Min ground
clearance
372 mm
Dry weight 92.7 kg
Warranty Three months, parts only
RRP (inc GST) $10,299 and $10,399 for Special Edition White/Red model

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