2005 Yamaha YZ450F

2005 Yamaha YZ450F - The Final Steel-Framed YZ450F

The 2005 Yamaha YZ450F was an evolutionary development of Yamaha's existing 450 motocross platform rather than a completely new generation. The basic 449 cc engine, four-speed transmission and steel-frame layout continued, but Yamaha refined the package as it prepared for the major aluminium-frame transformation that would arrive for 2006. That makes the 2005 model historically interesting as the final steel-framed YZ450F.

The liquid-cooled 449 cc DOHC five-valve engine retained its 95.0 x 63.4 mm bore and stroke and 12.5:1 compression ratio. Fuel came through a Keihin FCR flat-slide carburettor, giving the bike the immediate throttle response for which early YZ450Fs became known. On surviving bikes, worn accelerator-pump components, incorrect jetting and blocked carburettor passages can have a major effect on starting and response, making the MXOwners carburettor replacement and reference information useful when restoring the original system.

The unusual four-speed gearbox remained part of the YZ450F's character. Yamaha could use widely spaced ratios because of the engine's broad torque and because the motorcycle was designed specifically for motocross rather than trail or enduro riding. Suspension used 48 mm KYB inverted forks and a KYB Monocross rear shock, providing approximately 300 mm of front travel and 315 mm at the rear. Owners servicing the front end can refer to the MXOwners fork oil levels and suspension reference.

For today's owner, regular engine oil and filter changes, valve-clearance checks, clean air filtration and inspection of the cooling system remain particularly important. The engine and gearbox share the same oil supply, unlike some contemporary four-stroke motocross designs. Linkage, swingarm, steering-head and wheel bearings also deserve careful inspection on machines that may have accumulated two decades of competition use, with the MXOwners motorcycle bearing finder useful when identifying replacement components.

The 2005 YZ450F closed an important chapter in Yamaha motocross history. It still carried the steel-frame architecture descended from the pioneering YZ400F and YZ426F era, but its powerful 449 cc engine and developed suspension package were thoroughly established 450-class technology. One year later Yamaha would introduce an aluminium-framed YZ450F and begin another major stage of development, leaving the 2005 as the last of the original steel-framed Yamaha four-stroke motocross lineage.