1998 YZ400F
The machine was based on the experimental YZF400M factory motocrosser that competed in the 1997 Grand Prix season with factory rider Andrea Bartolini, and won several races in that season!

Designed to compete successfully against any type of machine - from a 250cc 2-stroke to large capacity 4-stroke - on any type of circuit - the new Yamaha YZ400F showed the way ahead in motocross bike design.

The 399 cc powerplant features a DOHC cylinder head and 5-valve design. With bore and stroke of 92 x 60.1 mm, it has a free-revving short stroke configuration designed to produce 55 HP with a wider powerband than the 250cc 2-strokes.

The short skirt piston runs in a ceramic composite plated cylinder which reduces frictional losses, thereby enhancing throttle response throughout the rpm range.

The chassis had 250cc class dimensions with exactly the same wheelbase, caster and trail as the sharp handling YZ250. Also the frame construction (the proven semi-double steel cradle) and the suspension specification was similar.
The dry weight was kept below 107 kg by the intelligent compact engine design and the use of lightweight materials for the engine internals. Also the left and right engine covers and cylinder head cover are made of magnesium.

The bike had a 5-speed gearbox and a manual decompressor for kickstarting.
The fuel tank contained 7.8 litres and the bike's colour was white with red and black accents.

For details, download the press text below.

1999 YZ400F
An important colour change for this year: the bike is now in blue colour!
On the technical side there are only a few small changes:

• New low-friction valve train
• Modified ignition curve on 3-dimensional mapped CDI
• Re-jetted TPS powerjet carburettor
• Longer rear shock
• New lighter more rigid swinging arm
• Improved seals around pivot bearings
• Lighter and smaller diameter rear hub
• Larger 22mm rear axle
• ‘99 YZ250-type rear brake assembly

2000 YZ426F
"More punch, less weight" was the theme for the 2000 model year.
The high tech 5-valve engine got a bigger bore, from 92 to 95 mm, which increased capacity to 426cc. To allow for the increased power, the engine got adjusted internal engine components, an uprated clutch, a redesigned Keihin FCR carburettor, a larger-diameter exhaust pipe and larger radiator capacity.
The gear ratios of 1st and 2nd gear were adjusted.

On the chassis side, the main frame was made stiffer by using stronger high tensile steel and the wheelbase was reduced from 1495 to 1490mm
The triple clamps were redesigned and the front fork and rear suspension uprated with lighter internals. The rear suspension's compression damping gets separate high-and low speed adjusters.
All this rendered a more precise and responsive handling.

By a new aluminium rear frame, the weight could be reduced by 1 kilogram.
Many other details were improved too, for example the new clutch lever with one-touch adjustment and the new front mudguard and radiator covers.

For details, download the press text below.

2001 YZ426F
The 2001 model comes with a range of detail changes.

Lightweight titanium valves and lower-rate springs which make for improved engine response. Complementing this higher-specification top-end are revised carburettor settings, as well as a revised ignition timing curve and a new low-friction crankshaft which work together to deliver instantaneous response.

Braking performance gets a boost for 2001 with the fitment of a new 250mm diameter floating front disc which replaces the previous model’s fixed 245mm design.  A new twin-pot Nissin caliper is operated by a redesigned three-piece brake lever and new master cylinder for strong and progressive stopping power.

At the rear end the YZ426F is now fitted with a lighter swinging arm which is manufactured from thinner 2.8mm high-tensile aluminium.

Further weight savings help keep the 2001 model’s overall weight down to 105.5 kg.

For more details, download the press text below.

2002 YZ426F
In 2002, Yamaha’s YZ and WR models (except the 85cc's) are equipped with a new swingarm that has been manufactured using Hydroform moulding technology – the first time that a motorcycle component has been produced using this method. The new Hydroform system utilises high pressure applied to the inside surface of the swingarm during manufacture, shaping it precisely to the required form.
The result is a greater lateral rigidity for more accurate rear wheel tracking. Other changes to the swingarm include lighter chain pullers and a larger diameter (18 mm instead of 17) swingarm pivot shaft.
Rear shock length is increased by 5mm to 492mm to accommodate the new swingarm, while settings are revised to match the new chassis.
The front forks features modified internals for smoother oil flow.

The rear brake disc is now 245mm in diameter – 5mm up on the 2001 design – and complementing this is a new rear brake caliper and bracket.

Another feature is a new front wheel. The bearing span in the front hub is increased by 20mm to 70mm for increased strength, and new tapered spokes change in diameter from 3.5mm to 3.2mm – a design that makes for improved handling performance and more accurate surface feedback.

For more details, download the press text below.

2003 YZ450F
New engine, new chassis and new bodywork: 2003 marked a big step in the development of the YZ-F.

Yamaha’s engineers fully exploited the FIM regulations that allowed 450cc 4-strokes to compete together with the 250cc 2-strokes in the MX1 category from this year onwards.
The engine has a larger stroke than the 426 engine, yet the outer dimensions are smaller! This is due to an ultra-compact cylinder head design with shorter valves.
The lighter valves and valve springs and lower frictional losses in the engine give the new engine an instant, 2-stroke type pick up at all engine speeds. Also the inertial moment of the crankshaft assembly had been reduced by 20% compared to the 426 model. And the engine is able to 'punch out' around 60 HP now!
To translate this super-low inertial mass and the machine’s wide powerband into enhanced traction, a 4-speed gearbox is used.
The newly designed camshaft is equipped with a lightweight automatic decompressor for easier starting.

Complementing this new engine is an all-new frame, still of the semi-double steel cradle design, but using super high-tensile steel (25% stronger than chrome-molybdenum steel) in selected areas and 'normal' high-tensile steel in the rest of the frame. This design allows it allow it to flexibly absorb external stresses while still retaining its stiffness. The new frame is a full 1.5 kg lighter than the YZ426F frame and actually lighter than many other manufacturers’ aluminium frames!

The bodywork of the bike is completely new, including a flatter seat, helping to optimise rider movement. Fuel capacity is now 7.0 litres.
Newly designed radiator air scoops deliver a 5% increase in cooling efficiency.

Weight saving was a key development target. The new all-titanium exhaust pipe assembly is a full 30% lighter. For reduced noise output the muffler size increased, and the 20mm longer tailpipe and cap are made of titanium.

Front and rear brakes are uprated and a host of detail weight savings are applied.

For more details, download the press text below.

2004 YZ450F
After the big change in 2003, smaller updates for 2004:
The front forks change from 46 to 48mm in diameter and are more flex resistant while also lighter. A special coating is applied to the outer tubes for smoother suspension action.
In accordance with this, the rear suspension receives new settings and the linkage system is slightly modified.
New titanium footrests have an additional row of teeth for more grips and are much lighter than the previous ones.
Yamaha’s policy has always been one of constant development and improvement of all components, and for 2004 the YZ450F is fitted with a host of other refinements too.

For more details, download the press text below.

2005 YZ450F
Detail improvements to the engine are aimed at enhancing overall controllability whilst retaining its user-friendly power output.
Intake ports and combustion chamber and ignition have been redesigned, the airbox is new. Also gearshifting is improved.

The new forks run with a separate oil chamber which is designed to give more stable damping. Fork protectors are redesigned for better coverage and less friction; they no longer need guides mounted to the fork outer tubes.

The bike also features a new swingarm. The arm width has been increased by 5mm to 42mm and the cast aluminium pivot assembly has also been redesigned. These changes not only modify the stiffness balance to give enhanced rideability, but they also achieve a weight saving of 500g.

Renthal aluminium handlebars are now original equipment. As well as giving improved feel, these proven bars give a weight saving of 90g.

For more details, download the press text below.

2006 YZ450F
The introduction of a new aluminium frame marks the introduction of the next generation YZ450F which sets new standards in performance, design and quality.
The bike also features radical new, factory bike inspired, ‘airflow’ bodywork and improved ergonomics give enhanced rider mobility.

There is also a new 5-speed (instead of 4-speed) transmission. On the 2006 model, 1st and 3rd gears use the same ratios as the 2005 machine, while 2nd is slightly higher and 4th a little lower. The additional 5th gear ensures that the YZ450F rider has a more versatile transmission that can deliver optimum power on everything from tight motocross tracks through to high speed ‘hare and hounds’ type events.

Compared to the previous model, the new YZ450F cylinder block has a more upright layout, sloping forward at only 4.5 degrees, to bring the machine’s centre of gravity closer to the rider. Together with the use of a new aluminium chassis, this idealised weight distribution makes for lighter handling performance and more agile cornering qualities.

Then engine also gets a new dry-sump lubrication system with the oil tank inside the crankcase. External oil pipes are thereby eliminated.
New radiators are lighter and smaller than before, and the new heated carburettor has revised settings.

The beautifully-finished semi-double cradle frame consisting of nine individual parts made from four different types of aluminium
The new frame has revised dimensions, and the result of this is a more compact chassis with improved mass centralisation, as well as a lower machine height. The 2006 bike has easier and lighter handling characteristics, making it a more ‘rider friendly’ package.
Suspensions are revised too by new internals, new triple clamps, new swingarm.
The shock absorber now features a lightweight titanium spring weighing 500g less than steel!
New taper-style handlebars are fitted as original equipment. They are mounted to adjustable clamps which allow the rider to opt for the standard position, or move the bars forward by 10mm.

For more details, download the press text below.

2007 YZ450F
Smaller changes for the 2007 include:
• Engine settings
• Titanium exhaust pipe (instead of the 2006 steel one) to save weight
• New lightweight triple clamps, made of forged aluminium instead of cast, with lighter bolts too
• Wave type front and rear disks
• Pro Taper handlebars

The bike is now available in an additional colour: white.

For more details, download the press text below.

2008 YZ450F
Modified intake ports, valve timing, cam profile and carburettor settings enhance the engine’s low to mid-range performance.
The 2008 engine can be distinguished from its forebears by the new matt black engine covers.

The new stainless steel silencer complies with the FIM 94dB(A) regulations and maintains the machine’s strong low to mid-range power output, while reducing overall noise.

The steering head pipe is slightly shorter and the lower triple clamps is lighter.
The front brake caliper is more compact and light.
The wave style disc now features elongated slots rather than the 2007 model’s round holes.
Front fork settings are adjusted and the fork protectors are made lighter too.
The rear suspension is also modified.
Footrests adopt the WR450F design, 55mm wide instead of 45, made of stainless steel.

For more details, download the press text below.

2009 YZ450F
The engine gets a modified ignition curve and matt black cylinder head cover.

Also on the chassis side there are detail refinements this year, again in the Yamaha philosophy of delivering the 'ultimate quick-turn performance'.  Regardless of the type of terrain or the layout of the track, most races tend to be won or lost in the corners and Yamaha has worked continuously to enhance the handling qualities of the YZ 4-stroke motocross models by optimising rigidity balance, keeping weight to a minimum, and centralising mass for lightness of feel during turning.

A new lightweight swinging arm features an asymmetrical cross section in its upper and lower portions for even greater levels of lateral rigidity. It also has redesigned cast parts at the pivot end which contribute to a 350g weight saving compared to the 2008 model. A revised linkage is fitted to complement it.
The rear wheel hub is lighter than before because a special new high-vacuum die-casting technique increases the strength of the material. The axle diameter increased from 22 to 25mm; the 3 wheel bearings together are lighter than the 2 bearings in the previous model.

The handlebar can now be mounted in 4 different positions on the clamps (previously 2 positions).
A lightweight DID 520DMA2 chain features highly-polished gold-coloured links.

For more details, download the press text below.

2010 YZ450F
With Yamaha's revolutionary engineering approach, the 2010 model is completely new from the ground up. The engine gets a 'reverse' layout with the cylinder slanted backwards and the intake at the front of the cylinder and exhaust at the rear. This allows the air cleaner to be put close to the steering head and the fuel tank under the seat. All this contributes to mass centralization for unprecedented handling and cornering!

The engine's intake tract is more straight and at the same time there is a wider bore/stroke ratio. This allows a more compact 4-valve (instead of 5-valve) design with pent-roof combustion chamber. The compression ratio is increased from 12.3 to 12.5 to 1 and cam profiles are adjusted. Result: impressive power delivery at all rpm!

Also new is the fuel injection system, with 44mm Keihin throttle body and 12-hole injector for superb fuel atomization. With fuel injection the combustion is always optimised no matter what altitude or temperature conditions are on the track.
The system is programmable, so the rider can create his own preferences regarding the power delivery. This can be done by an accessory "YZ power tuner" which is easy to use without having to resort to a PC!

The rear exhaust pipe has a resonator integrated and makes a 'tornado style' bend in order to achieve enough length for strong low- to mid range power.
Cylinder head cover, clutch cover and oil filter cover of the engine are made of lightweight magnesium and the valves are still of titanium.

The chassis is newly constructed and suspensions are optimized
Fuel tank size is reduced from 7 to 6 litres and the translucent material allows to check the fuel level.
The bodywork of the bike is all new with an aggressive look.

For more details, download the press text below.