2005_YZ450F_Press Release

2005 YZ450F
Utilising much of the same advanced engine and chassis technology that has taken
Yamaha factory rider Stefan Everts to the MXGP Motocross Championship, the
YZ450F is today’s leading contender in the premier category. The 2005 model
benefits from a range of changes to the engine, as well as a number of chassis
modifications which are also found on the entire YZ motocross range.
Engine
Its 450cc 4-stroke 5-valve DOHC engine has undergone a series of detail
improvements that are aimed at enhancing overall controllability whilst retaining its
user-friendly power output.
New cylinder head and piston
Featuring 5 titanium valves, the YZ450F benefits from one of the most advanced and
efficient cylinder head designs and for the new season this class-leading technology
has been refined even further. The shape of the outer rim of the combustion chamber
and piston have been modified to achieve better combustion efficiency, which in turn
improves the engine character whilst making it more controllable.
Reshaped intake port
Yamaha’s engineers have also redesigned the intake port in order to increase the inlet
gas flow speed, which has a positive effect on the engine character.
Modified carburettor
Detail changes to the carburettor include a movable fuel pipe joint for easier
serviceability and the addition of a leak jet for improved acceleration. The joint
between the carburettor and airbox has also been modified and features additional
ribbing for improved durability.
New airbox
For improved driveability and a more rider-friendly engine character, the 2005
YZ450F is equipped with a new airbox which has a completely reshaped funnel-type
inlet between the air filter and carburettor.
Lighter clutch action
Primary reduction ratio is changed from 62/22 (2.82) on the 2004 model to 61/23
(2.65) on the 2005 machine and the clutch spring rate is reduced by 6% to give easier
action and a lighter feel.
Smoother shift feeling
As well as its smoother action clutch, the YZ450F also benefits from an improved
shift shaft assembly which features a redesigned lever, shaft and guide. The combined
effect of the new clutch and smoother shift feeling is to enhance overall rideability.
Optimised ignition timing
The 2005 YZ450F is equipped with a new CDI unit which has been designed to
optimise ignition timing thereby enabling the latest version of this high performance
competition engine to produce an even more controllable power output.
Chassis
The 2005 YZ450F features the following chassis changes:
• New twin chamber type front forks.
The new forks run with a separate oil chamber which is designed to give more stable
damping, while a new transfer control valve is adopted for improved middle to full
stroke performance. In addition to these technical changes to their internals, the latest
forks use a different specification of fork oil which has been selected to offer better
feel.
• Newly designed triple clamps
Front end handling performance has also been sharpened up by the use of newly
designed triple clamps. The underside of the upper clamp features a revised ribbing
design, while the lower triple clamp has repositioned pinch bolts with a reduced pitch
of 21mm, which is 5mm less than previously.
• Lighter, high rigidity aluminium swingarm
The 2005 bike features a new lightweight 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.
• Modified rear suspension linkage collars
Detail changes have been made to the swingarm linkages, which now utilise onepiece straight collars whose thickness is increased by 0.5mm to 2.5mm.
New design bearings are also fitted to accommodate the new one-piece collars. The
bolt that secures the linkage assembly to the main frame is reduced in diameter by
2mm to 14mm and the collar thickness is increased to 3.5mm. These changes make
for smoother suspension action and also help to facilitate routine servicing of the
linkage assembly.
• New rear shock absorber with rebound oil lock system
To complement its uprated front forks and improved linkage and swingarm, the latest
YZ450F is also equipped with a higher specification rear shock absorber. This new
shock features a rebound oil lock system which makes for more stable suspension
action on the rebound stroke, which gives improved handling performance.
• Re-routed front brake hose
On the 2005 machine the re-routed front brake hose exits the top of the twin piston
caliper and goes upwards, passing the inner side of the left hand fork tube and then
continues up the front of the forks to the front brake lever. This new layout allows the
use of a shorter, straighter brake hose which gives improved feel at the lever and
facilitates brake bleeding, as well as eliminating the need for a plastic hose protector
at the base of the left fork leg.
• Wrap-around self-supporting fork protectors
Close attention to detail is evident throughout the new bike and the new fork
protectors are a typical example of how Yamaha’s designers have worked hard to
improve component design and functionality.
These new protectors feature a rounder profile that wraps around each fork tube to
give approximately 270º of coverage, which dramatically improves the protection of
the inner fork tubes and helps to extend seal life. These new protectors are also selfsupporting, so they no longer require guides mounted to the fork outer tubes. This
new design eliminates guide/protector friction giving smoother fork action, especially
in muddy conditions.
• Renthal aluminium handlebars
A machine built to such a high specification deserves high quality handlebars, so the
2005 YZ450F comes fitted with aluminium Renthal bars as original equipment. As
well as giving improved feel, these proven bars give a weight saving of 90g.
• Lightweight rear brake caliper mounting bracket
Detail changes to the rear brake caliper mounting bracket include a new-shape ‘key’
section that slots into the guide in the swingarm, saving 35g. And for easier rear
wheel installation, the rear wheel collar features an extended chamfer on its rear
section that helps guide the wheel into place.
• New swingarm seal guard featuring an EPDM sponge and narrower chain
guide
For reduced chain noise, the 2005 bike runs with a new swingarm seal guard featuring
an EPDM sponge, as well as a narrower chain guide.
• Newly designed rear sprocket
A newly designed rear sprocket uses uniform width teeth (instead of tapered teeth) for
increased durability and reduced chain chatter.
• New hexagonal head bolts replace various cross head and Allen-type fixings
YZ450F technical highlights
Engine
• New cylinder head with reshaped combustion chamber
• New piston
• New shape intake port
• Modified carburettor and joint
• New airbox with funnel-shaped inlet
• Lighter clutch action
• Reduced primary reduction ratio
• Smoother shift feeling
• New CDI with optimised ignition timing
Chassis
• Newly designed high rigidity aluminium swingarm, 500g weight saving
• Uprated rear suspension linkage
• Twin chamber type front forks
• More rigid upper and lower triple clamps
• Rear shock featuring full rebound oil lock system
• Wrap-around self-supporting fork protectors
• Shorter and straighter front brake hose
• Renthal aluminium handlebars
• Lighter rear brake caliper bracket
• Hexagonal head bolts replace cross head and Allen-type fixings
• Modified swingarm seal guard and chain guide
• New non-tapered teeth on rear sprocket