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2010 Kawasaki KX450F

2010 Kawasaki KX450F2010 KX450F

Already ranked at the top of its class in numerous enthusiast magazine shootouts, for 2010 the KX450F
receives a number of engine and chassis updates to ensure its winning potential.

The KX450F base package provides an excellent platform for experienced racers to win races in the top
classes. Design of the highly rigid aluminium frame, suspension components and settings focused on
delivering superb high-speed stability – especially in straight lines – to enable race-experienced riders to ride
full out. And to deliver holeshot-winning performance – a key factor that can mean the difference between running up front and winning, or getting stuck mid-pack – chassis geometry and the hard-hitting 4-stroke engine’s wide powerband were designed to maximise rear wheel traction. The combination is a proven race-winner, with Kawasaki racers regular podium finishers.

To keep the Lime Green racers out in front, Kawasaki engineers made a number performance-enhancing updates to both engine and chassis. Feedback from factory racers resulted in a number of refinements that deliver increased high-rpm and over-rev performance. The new engine has specs on par with Ryan Villopoto’s KX450F racer. Also inherited from the racing world, a new piston with bridged-box bottom makes its first appearance in a mass-production machine. Finally, fine-tuning of the clutch results in improved
clutch feeling.

Chassis updates focus on making the KX450F even easier to ride fast. Revisions to the frame and uspension components result in lighter handling, improved suspension action, increased comfort and greater cushioning when landing jumps. Already acclaimed as the best looking motocrosser in the paddock, the KX450F once again sports sharp factory-racer looks that are more than skin deep. Sleek, functional bodywork was designed to offer racers a slim rider interface to further facilitate going faster.

The KX450F – designed to give racers the competitive edge to run out front.

Fuel-injected 449 cm3 liquid-cooled, 4-stroke Single delivers hard-hitting power from low- through high-rpm. The broad powerband and responsive throttle offer a broad spread of torquey response that enables racers to get on the gas and go even from down low. In addition to the inherent benefits, fuel injection contributes to the KX450F’s lag-free acceleration, especially after landing jumps. For 2010, a number of refinements, including the first mass-production use of a high-performance piston featuring a bridged-box bottom, offer improved performance in high-rpm and over-rev ranges, and modifications to the clutch
deliver improved clutch feeling.

New piston, featuring the same design used on our factory racers, offers improved performance at all rpm.
A revised profile with a shorter skirt, reinforced external ribs and the first mass-production use of a bridged-box bottom, featuring fully flush internal bracing, results in a lighter, stronger piston.

Shorter piston pin has a smaller inner diameter for increased strength.

Intake camshaft with revised sprocket/shaft arrangement moves intake valve timing 2o forward, to suit revised engine characteristics.

Crankshaft with a slightly higher inertial mass (47.2 kg-cm2 >> 48.2 cm2) offers increased traction
performance. The balance factor is unchanged. Wedge-shaped crank web increases offsetting moment
for high crankshaft balance factor. At close to 60%, the balance factor of the ’10 KX450F is on par with Ryan Villopoto’s factory racer. The result is reduced engine vibration, smoother power delivery and increased performance – especially at low rpm, where response is noticeably snappier.

Refined power delivery

In addition to generating the electrical output necessary to ensure easy starting, the large-diameter ACG also contributes to engine feeling at partial throttle.

One-piece stainless steel exhaust pipe is 40 mm shorter, contributing to improved mid-high range performance. The optimised pipe line contributes to improved ergonomics, and the new steel construction
offers enhanced durability.

On European models, revised internal construction results in a silencer approximately 330 g lighter (on par with that of other markets). Material trimmed from the spring holders and outer surface of the operating plate optimise rigidity and improve oil drainage from the clutch, contributing to more direct feel.

Friction plates feature approximately 75% more friction material, contributing to a more direct feel (particularly beneficial for hooking up after landing jumps).

Operating plate pusher with increased outer diameter reduces clearance between the pusher and the hole of the input shaft, improving clutch operation.

The following clutch revisions offer more direct feel and increased control. Improved clutch feeling

Designed specifically for motocrossers the fuel injection system incorporates a small lightweight ECU and operates without a battery to further eliminate unnecessary weight. And of course, fuel injection eliminates the need to adjust engine settings to suit track and climate conditions.

Ensuring quick starting without a battery was a prime directive when developing the KX450F’s fuel injection system. Using only electricity generated by the kick starter, the engine can be started with only three rotations of the crankshaft. The system delivers electricity in the following order: 1) ECU, 2) fuel pump, 3) injector. With a warm engine, starting can be accomplished in a single kick.

The compact, lightweight ECU, located just in front of the steering head (behind the number plate), was designed specifically for motocross use. To help cope with the shocks and vibrations of motocross riding, the fuel pump relay is built in to the ECU.

An optional KX FI Calibration Kit (containing KX Racing software, an ECU controller, mounting bracket and damper, harness and USB cable) allows racers to adjust engine characteristics (by rewriting actual data maps) to suit their preference. (In addition to the kit, a PC and 12 V battery are all that is required.) Please refer to the Appendix for more details.

The 43 mm throttle body makes use of a progressive throttle link to deliver airflow in much the same way as would a FCR carburettor. Using two linked shafts, the throttle body opens more quickly after the 3/8 open position, delivering sharp response and excellent power feeling.

Ultra-fine atomising injector with 12 holes sprays particles with a droplet size of 60µ for smooth power deliver and improved engine at partial throttle. The injector was set at 45o, the optimum angle for improved mid-range power. Lightweight flat-bottom aluminium fuel pump is located in the plastic fuel tank.

To ensure a stable fuel supply during vigorous motocross riding the fuel pump features a rubber fuel filter cover that wraps around the inlet port and acts as a fuel trap. A fuel return hose from the pressure regulator ensures there is always fuel in the fuel trap.

New ECU operating programme and revised setting data offer improved response at low-mid rpm. Battery-less fuel injection system

The engine was tuned such that the torque curve follows the limit of running resistance for as long as possible. (Unchecked, engine torque can exceed this limit, resulting in wheel spin, which does nothing to help
forward momentum.)

Efforts were made to achieve the widest possible torque band, so that traction efficiency would be maximised for a greater part of the rev range.

The engine is almost upright (forward lean angle is 3o) to help place the bike’s centre of gravity in the ideal position for maximum traction.

Asymmetrical high-acceleration cams yield high intake efficiency.

During the cylinder head casting process, the cores for the intake ports were given a special coating to make the intake ports smoother. The extremely smooth surfaces that result increase intake efficiency at all rpm.

Lightweight titanium valves (IN: 36 mm; EX: 31 mm) reduce reciprocating weight and offer high-rpm reliability.

Aluminium valve spring retainers reduce reciprocating weight for reliable valve control at high-rpm.

Double valve springs also help ensure stable valve operation and allow a short cylinder head height.

Cylinder skirt was strengthened to match the increased engine performance.

New thicker (22 mm >> 32 mm), wider (120.2 mm >> 127.8 mm) radiators with increased fin and tube pitch are stronger, offer better resistance to mud build-up, and maintain cooling performance. Because the new radiators are stronger, reinforcing brackets could be eliminated, resulting in lower overall weight.

Other performance-enhancing engine characteristics

The screw-type adjuster on the cam chain tensioner is equipped with a pressure spring. Because the system automatically minimises the vibration caused by a loose cam chain, it greatly reduces the chance of a mishap during a race. (Non-automatic systems that are tuned incorrectly can actually adversely affect valve timing by putting too much pressure on the cam chain.)

The combination of the smooth-shifting, close-ratio 5-speed transmission with the KX450F’s low-rpm engine performance offers the rider the option to shift to a higher gear when traversing rough sections. Since this reduces the effect of sudden (unwanted) throttle input, allowing focus to be given to racing rather than careful throttle control.

In the event of a stalled engine during a race, getting it started again as soon as possible is a racer’s first priority, so the KX450F is equipped with an automatic compression release (ACR) system. The dual-weight centrifugal decompression system fitted to the exhaust cam eases starting in much the same way as a conventional lever-type system.

Sprocket-style chain drive roller helps smooth engine braking by reducing the effect of driveline lash when the rider gets off the gas quickly and play in the lower side of the chain suddenly tightens. The additional control facilitates corner entry.

The KX450F’s slim aluminium perimeter frame is a lightweight construction composed of forged, extruded and cast parts. Chassis balance and settings were all set to suit race-experienced riders. The centre of gravity and key dimensions (swingarm pivot, output sprocket and rear axle locations) were chosen so that the rear tyre would drive the bike forward (instead of causing it to squat). For ’10 revisions to the frame and
suspension components were designed to offer lighter handling, improved suspension action, increased comfort and greater cushioning when landing jumps.

While the frame remains essentially the same as that of the 09MY model, a revised steering stem shaft and new swingarm offer improved handling.New steering stem shaft with lower rigidity contributes to lighter handling. Swingarm with revised cross-section also contributes to lighter handling. The alloy swingarm uses a cast front section, tapered hydroformed spars and forged chain adjusters.

Lighter-handling chassis

  • The New Uni-Trak rear suspension system mounts the suspension arm below the swingarm, allowing a longer rear suspension stroke. The longer stroke in turn allows more precise rear suspension tuning.
  • Revised linkage ratios for the New Uni-Trak rear suspension further increase rear traction performance.
  • Extensive rider testing was conducted to determine the ideal linkage ratios and rear shock absorber damping settings to achieve maximum rear wheel traction. Superior rear wheel traction
  • Kayaba AOS (Air-Oil-Separate) fork keeps oil and air in 9 10 separate chambers for stable damping performance during long motos. Low-friction fork seals contribute to smooth action.
  • Revised spring rate, revised damping settings and the less rigid steering stem offer improved action (especially at the initial part of the stroke) and increased comfort.
  • A super-hard DLC coating (Diamond-Like Carbon) on the outer surface of the inner fork tubes reduces sliding friction (and stiction) and gives better action, contributing to the smoother ride. The coating is even effective when the fork is exposed to lateral forces that would usually hamper slide action, such as during cornering. The increased surface hardness also minimises scratches and damage to the tubes.
  • Friction-reducing Kashima Coat on the inside of the fork outer tubes contributes to smoother suspension action (especially at the initial part of the stroke) and a better ride feel.
  • Revised shock spring rate and damping settings contribute to increased stability and offer improved
    cushioning when landing jumps.
  • The rear shock features dual compression adjustability, allowing high-speed and low-speed damping to be tuned separately.
  • The rear shock also features the Kashima Coat on the tank cylinder. The reduced friction smoothes
    suspension action.

Race-oriented suspension

  • The KX450F features petal brake discs front and rear. In addition to helping reduce unsprung weight, the wave shapes of the petal discs help clean the brake pads for more efficient braking performance.
  • Revised rear brake pad material offers stronger braking.
  • Rear caliper guard protects the caliper from damage.
  • A factory-style Renthal (standard-type) aluminium handlebar is standard equipment.
  • Rib-less rear hub and butted spokes reduced unsprung weight.
  • Rims are coated in black alumite – just like our factory racers.
  • Factory-style graphics complement the KX450F’s highly tuned performance.

Factory-style and other race-oriented components

Designed with rider ergonomics in mind, bodywork components offer the rider a slim interface, the natural position making it even easier for racers to go fast.

Formed using a double-injection moulding process, 2-tone shrouds contribute to the slim package. Fine-tuned to accommodate the new radiators, the shrouds feature a slightly slimmer design. 2-tone side covers are also formed using a double-injection moulding process. Like the shrouds they contribute to the slim package. A hole in the right-side cover helps cool the silencer.

Rider interface

The frame widens at the ankles to offer the rider better grip and narrows near the bend below the seat to allow a slim riding position. The optimised pipe line of the exhaust contributes to improved ergonomics. Slim seat features firmer urethane which keeps its original shape longer. The seat uses a slip-resistant top surface for good grip when seated and smooth sides for excellent rider mobility.

Wide (front-to-rear) footpegs designed to offer grip and superb feel at the pegs. The clutch cable boot features a large quick adjuster, making it easier for riders to adjust play in the clutch cable. Throttle grip has a unitised collar. The one-piece unit provides additional stability during throttle operation.

Lightweight short-length grips feature a pattern designed to provide excellent grip.

Additional Features

  • Fast-idle knob on the throttle body allows riders to increase engine speed when first starting a cold engine.
  • The crankshaft and connecting rod received a carburising and quenching treatment for additional rigidity.
  • The camshaft lobes and tappet surfaces feature a soft-nitriding surface treatment for long wear and high-rpm reliability.
  • A large flap inside the air cleaner case helps prevent the ingress of mud.
  • The silencer uses long-fibre packing which is much more resistant to being blown out of the tail pipe than standard length packing. As a result, packing needs to be replaced half as often.
  • Rubber damper collar used for the rear silencer mount also contributes to increased durability.
  • Right-side crankcase is reinforced at the lower engine mount for increased strength and durability.


  • Designed to accommodate the in-tank fuel pump, the plastic fuel tank is formed using a rotational moulding (or rotomoulding) process that reduces weight.
  • Large synthetic skid plate offers great protection with minimum weight.
  • Revised front fender is thicker and more rigid. (Photo 18)
  • New chain with thinner inner links offers 20 g in weight savings.
  • All markets now feature Bridgestone tyres (F: M403; R: M404).