2010 Yamaha YZ450F - First Look

There hasn't been this much hype about a new motocross bike in a long time, perhaps since the introduction of Yamaha's own YZ400F back in 1998, the bike that started the modern MX four-stroke revolution. Rumors on forums and speculation on the web have been rampant, but the new YZ450F definitelylives up to the chatterby delivering a radical new take on the single-cylinder motocross bike.

First of all, yes it's true, the cylinder head is backward, with the airbox, intake and throttle body (yes it's fuel-injected) residing in front of the engine and the exhaust passing out the back into a "tornado-style" header (think curly fry) and then into the traditional silencer. But there is a lot more to this engine. The cylinder is slanted rearward for improved mass centralization and straighter intake and exhaust ports. Another key change is that the cylinder is offset forward of the crank's center so that the connecting rod is vertical as combustion begins, thus reducing friction and maximizing power. Internal dimensions are changed, with a larger 97.0mm bore and shorter 60.8mm stroke; the compression ratio has been bumped to 12.5:1.

Still not convinced it's all-new? How about the fact that Yamaha has abandoned the five-valve head in favor of four titanium valves in a pent-roof combustion chamber. As for the battery-less fuel-injection system, a 44mm Keihin throttle body with a single 12-hole injector meters fuel/air mixture, while an optional GYT-R accessory power tuner allows owners to fine-tune mixture and timing to personal preferences and for track conditions.

The chassis features an all-new aluminum Bilateral Beam frame made up of a combination of 16 pieces, including forged, cast and aluminum components. The beams form a pair of "S" bends. The first can be seen in a profile view, while the second can be seen in photos looking down from above the stripped frame. Front suspension is by a KYB speed-sensitive fork with 10mm more stroke and new damping. Out back is a redesigned KYB shock that has been optimally placed in the space vacated by the airbox and features a larger-capacity remote reservoir and fatter 50mm piston. New triple-clamps change offset from 25 to 22mm for better handling but still retain the four-way adjustable top-clamp with Pro Taper bars.Hidden behind the new split radiator shrouds is a fuel tank that carries its contents closer to the bike's centerline for better mass centralization. It is now made from a lighter-colored gray plastic so that fuel level can be monitored easier while filling. Brand-new bodywork gives the YZ a crisp, modern look, while engine covers and sidepanel materials have been improved for better wear resistance.

No price has been set yet, but stay tuned for a riding impression in the near future.