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BIG-BORE GREENIE: Kawasaki is the last of the Big Four to join the Big-Bore Four-Stroke Wars.

Big-bore Kawasaki motocrosser here

December 6, 2005

Kawasaki's 2006 KX450F has arrived in South Africa. The Green Meanies' flagship dirtdigger has a new DOHC, 449cc, quad-valve big-bore engine in a trick aluminium frame.

The gaping 96mm bore provides plenty of room for the in the cylinder head for the four big titanium valves (36mm inlet, 31mm exhaust) with double valve springs and aluminium retainers to deal with the high revs resulting from the short 62.1mm stroke.

The camshaft lobes and tappets have been nitrided for wear resistance, the crankshaft and connecting rod are hardened for rigidity and the new KX450F is the first KX to receive a low-friction coating on its piston skirt.

There's a centrifugal auto decompression system that rotates the exhaust camshaft to drop the compression ratio for easier kick-starting and a hot-start lever on the left handlebar handlebar so you can get going again quickly after a stall or fall.

The engine drives through a conventional wet clutch and four-speed gearbox.

Chassis

Kawasaki engineers have combined the techniques they developed in building the ZX-10R alloy frame with the geometry of the earlier steel perimeter KX frames to make a composite aluminium perimeter frame, welded together from forged, extruded and cast aluminium sections.

Titanium footpegs and hangers, a titanium exhaust heat guard, slim lightweight radiators and an aluminium sump-guard are used to keep the bike's weight down to 100kg.

It has titanium footpegs and hangers, a titanium exhaust heat guard and an aluminium sump-guard

Kawasaki also used aluminium rather than steel for the tank and seat retaining nuts and brackets, the front brake hose clamp and the clutch cable elbow and fitting nuts.

The slim design of the frame and the two-piece radiator shrouds leave the upper frame spars exposed, to make the bike look and feel light and narrow.

Suspension and brakes

The 48mm inverted Kayaba forks are adjustable for compression and rebound damping; their air and oil are kept in separate chambers for stable performance during long races, with low-friction seals for smooth action throughout their 315mm travel.

At the rear a Kayaba monoshock adjustable for preload, high-speed and low-speed compression modulates the movement of an alloy swing-arm with tapered spars and Uni-trak linkage.

Slowing down is entrusted to a 250mm semi-floating petal disc with a twin-piston floating calliper in front and a 240mm disc with single-piston calliper at the rear.

Renthal aluminium handlebars are standard and the seat is topped with non-slip fabric.

Kawasaki accessories for the KX450F include mounting clamps for oversized handlebars, aluminium and steel sprockets for changing final drive ratios, solid petal brake discs for racing in the wet, optional springs for the front forks and rear shock and a 20" front wheel.

TORQUE IS THE NAME OF THE GAME: and the 450cc motocrossers have plenty of it.

TOP-DRAWER SUSPENSION: The KX450F has 48mm upside-downies in front and a multi-adjustable Kayaba monoshock at rear.