YAMAHA’S RADICAL NEW YZ450F

In a time of economic conservatism when large companies are treading water, Yamaha’s introduction of the their radical new YZ450F is a welcomed shot of adrenalin for the dirt bike world. This machine is ground breaking in design, looks and technical advancements so without further ado, here’s a look at the new machine.

 

 

 

 

ENGINE

The motor is all-new with a rearward slant, positioning the top-end mass towards the center of the bike to provide a lighter feel and more nimble handling. This new position with the addition of EFI gave Yamaha the freedom for a completely new layout, allowing a straight intake and exhaust port. The intake is now in the front of the engine, with the exhaust out the back where last year’s carburetor sat. Here’s the rest of the tech briefing concerning the powerplant:

• A tunable, battery-less fuel injection system with a 44mm Keihin throttle body and a 12-hole injector feeds the new motor.

• The cylinder is offset to the front of the crank center so the connecting rod is more vertical at the moment of greatest combustion force. This allows the force to transfer vertically down the connecting rod as opposed to vertically and horizontally. This minimizes piston friction and is a more efficient use of combustion.

• The bore is now larger, 97.0mm, and the stroke is shorter, 60.8mm. The compression is higher on the new motor at 12.5:1. The 2010 head uses four titanium valves (last year it was a five valve) with a “pent-roof” design combustion chamber. The intake and exhaust cam’s profiles are changed to increase the valve working angle and valve lift.

• Since the exhaust leaves the back of the head towards the shock, a new “tornado-style” exhaust header with resonator winds its way to the back. This compact design also keeps weight towards the center of the bike.

• A new clutch actuator arm ratio makes for a lighter and smoother lever feel. New transmission gear dog shapes and a new shift drum help for smoother shifting.

CHASSIS

The all-new aluminum bilateral beam frame is crafted from a combination of 16 forged, cast and extruded aluminum pieces. It’s designed for ideal rigidity, balance and light weight. A unique double “S” bend main beam design provides the flex needed for good handling. Here are more details:

• The KYB Speed Sensitive front fork has a 10mm longer stroke with revised low-speed damping to match the new frame rigidity.

• The swingarm and the KYB rear shock are redesigned to position the shock along the central axis of the frame and angled more towards the center of the machine. Yamaha has used the space once occupied by the airbox to line the shock up. The shock now features a larger capacity piggyback reservoir and larger 50mm piston.

• The new gas tank is center-mounted in the frame and extends underneath the seat towards the bike’s center point. The tank is now gray-colored and slightly transparent to see the fuel level.

• The new triple clamps have an offset of 22mm; last year’s were 25mm. The Pro Taper bars are four-way adjustable.

• The new air filter layout allows for a straighter intake and improves weight balance. It also keeps the dirt and dust kicked up from the rear tire away from the intake system. The two-piece radiator shrouds are now intakes for the airbox.


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