YZ 450F 4-stroke Liquid Cooled Motocross

The YZ450F features a revolutionary fuel injected, liquid-cooled, 4-stroke, 4-valve, DOHC, rearward-slanting single cylinder engine and an advanced Bilateral Beam aluminium frame with components distributed for a perfect mass-centralisation and class-leading handling.

Unique engine design features a rearward slanting cylinder that is "reversed" compared to traditional designs. The FI throttle body and air box are front mounted while the exhaust exits from the rear of the cylinder. This design is used to centralize mass for excellent handling and a light feel. The other major benefit is the straight shot intake system which maximizes power output. The engine is slanted 7.5 degrees rearward.
The "reversed" design allows for a straight intake path into the cylinder, providing maximum intake flow and efficiency for excellent power. The front positioned intake means that engine heat will have less "heating effect" on the incoming fuel charge (cooler fuel helps increase power).
Centrally located spark plug and the 4-valve head promotes a "tumbling effect" of the inbound fuel / air for better combustion, improved throttle response and power output.
Compact, 4-valve cylinder head design, features a 12.5:1 compression ratio. The intake valves are 36mm in diameter and the exhaust valves are 30mm.
Lightweight titanium valves (intake & exhaust) and load-reduced oval valve springs reduce reciprocating mass for less friction, faster-revving and smoother-hitting power delivery across the rev range.
Automatic cam chain tensioner reduces maintenance and cam chain "sliders" reduce internal frictional losses.
High performance, light weight hollow intake and exhaust camshafts.
The lightweight aluminium cylinder features a ceramic composite coating which is applied directly to the aluminium, eliminating the need for a heavy iron sleeve or liner. The ceramic coating insures faster, more uniform heat dissipation, reduced friction and a longer service life.
The cylinder is "offset" relative to the crankshaft to reduce frictional losses between the piston and the cylinder wall during the power stroke. This offset design is a first on a Yamaha motocross machine.
Crankcase design utilizes an integrated oil tank inside the cases to supply oil to the dry sump lubrication system. This design concentrates mass lower in the frame for optimum handling and lighter weight feeling. There are no exterior oil lines with this design and the internal oil tank is designed to promote air - oil separation.
Special cylinder design features cutaways that allow the air "trapped" under the piston to enter a side chamber (or cutaway) to reduce horsepower-robbing "pumping losses."
The crankcase also utilizes cutaways to reduce "pumping losses". The crankcase cutaways match the cutaways in the cylinder for maximum efficiency.
Lightweight , short-skirt, forged piston provides excellent reliability, less mechanical vibration and reduced weight.
Piston oil cooler utilizes a pinpoint nozzle that directs oil to the desired portion of the cylinder and underside of the piston, which reduces piston, cylinder and rod temperatures for great durability.
Oil volume in the engine has been optimized to reduce weight and oil drag related power losses.
Lightweight gear driven balancer shaft reduces vibration for improved rider comfort and less rider fatigue.
The crankcase features a tri-axis layout for the crank, main and drive axles. This tri-axis design keeps the crankcase more compact while also centralizing mass for excellent handling. All of the shafts are positioned low in the cases to maintain a low centre of gravity.
5-speed transmission features "involute splines" on the transmission axles to ensure smooth shifting and instant hook-up under power. The multi-plate wet clutch features a revised clutch lever actuating arm (engine side) to reduce excess free play as the clutch heats up during a moto.
5-speed transmission optimizes engine performance. This 5-speed transmission provides great performance and makes the YZ450F very versatile for MX, Hare Scrambles, Super Moto, Ice Racing and Enduro type applications.
Quick-access, lightweight magnesium outer clutch cover for fast, easy clutch maintenance.
Keihin 44mm throttle body fuel injection system is a battery-less design for reduced weight and is designed specifically for MX applications. The 12-hole injector maximizes fuel atomization for more complete combustion and great power output. The benefits of fuel injection include constant ongoing adjustments to insure the optimum fuel - air ratio regardless of outside air temperature and altitude. Other benefits include improved starting and improved throttle response. The system is equipped a throttle position sensor (TPS), plus a range of sensors (engine temp, outside air temp and air pressure etc.). There is also a cold start and fast idle knob which doubles as an idle adjuster too.
The injector spray pattern, spray direction and the distance to the intake valves have been optimized, while the specially designed straight intake tract helps to maximize the benefits of the FI system and overall power output.
Optional, compact, hand held "YZ Power Tuner" allows tailoring of both fuel injection settings and ignition mapping. Nine (9) different setting points can be accessed for both the FI and ignition maps. Maps can be stored and shared with other Power Tuners if desired. The days of removing a carb to make jetting changes are gone.
Compact, lightweight in-tank electric fuel pump
Larger capacity ACM (alternating current magneto) is used to eliminate the need for a battery.
Automatic decompression system ensures easy starts in any gear with no manual lever to fuss with.
Air box (located behind the steering head) features a straight shot intake boot and a washable, dual-stage, foam air filter.
"Tornado" design exhaust system exits from the "rear" of the cylinder. The spiral winding of the header pipe provides the correct "tuned" length and takes full advantage of the exhaust "pulse" effect to maximize cylinder filling. There is a "resonator" (or power chamber) built into the header pipe. Another benefit of this exhaust system is mass centralization
Re-packable lightweight aluminium / stainless steel muffler has been designed to optimize the performance of the engine. Muffler disassembly is easy since the silencer bolts together with allen screws.
Compact, lightweight, single core, dual radiators provide outstanding cooling efficiency.
High powered ECU controls the ignition and fuel injection processes. There is also a "G" sensor system that will shut down the fuel injection system if the bike lies on its side for more than 10 seconds. There is no special procedure to re-start the bike … just kick it and go.
Works-style race-spec "barrel adjuster" for on-the-fly clutch adjustability.
Easy access oil filter.

Compact "bilateral beam" aluminium frame centralizes mass for exceptional handling. This 450cc class specifically designed frame consists of a "High Solid Die Cast" head pipe, hydro formed main rails plus various forged and extruded components. This frame is compact and offers significantly improved "rider - machine communication" (a.k.a. feedback). The engineers have optimized the balance between strength, rigidity and flex. The key goal of the chassis is faster and easier cornering … one of the keys to winning races. The engineers started with a clean sheet of paper and designed the chassis based on the requirements of a 450cc motocrosser. Note: the YZ450F frame is unique, it is not the same as the YZ250F frame.
The rigidity balance of the frame has been optimized and features high lateral and torsional rigidity with "tuned flex" in the longitudinal direction. The result is a feeling of lightness, agility and traction.
Lightweight, tapered, aluminium swingarm is produced using "hydro forming", a special method that uses high pressure liquid to form shapes. The shock is positioned in-line with the central axis of the bike. The swingarm pivot shaft is now 17mm.
Lightweight removable rear sub frame is constructed of square-section, lightweight aluminium pipe. The detachable design allows easy access when servicing rear suspension components.
Cast aluminium upper and forged aluminium lower triple clamps. Fork off set is 22mm.
Adjustaable handlebars offer a total of 4 different handlebar positions available (thanks partly to the offset design of the aluminium handlebar clamps) with an adjustment range of 30mm, to suit a wide variety of riders.
Pro Taper bars provide excellent strength and durability. Foam handlebar pad is included.
48mm, adjustable, inverted, Kayaba cartridge forks with 310mm (12.2") of wheel travel. These forks feature a twin-chamber design which means the damper unit is in a separate structure which prevents aerated fork oil from entering the inner damper assembly and reducing its damping abilities. Since the inner damper is pressurized, it also eliminates bubbles forming in the oil. Front fork adjustments include: 20-way compression damping and 20-way rebound damping. Optional fork springs are available through Genuine Yamaha parts.
The balance between the inner and outer tubes is optimized, while the Kashima coating on the pressure tank and the piston rod reduce friction for smoother suspension performance. The cylinder diameter is 24mm for excellent primary cushioning.
The 48mm inverted KYB fork also features a Transfer Control Valve (TCV). The TCV enhances the damping force from mid to full stroke and improves bottoming characteristics. The benefit of TCV is more precise control throughout the full suspension stroke. The TCV is located on the upside of the spring and its function is controlled by piston speed, not piston position … hence the term "Speed Sensitive fork".
"Kashima coating" has been applied to the fork tubes to reduce friction for smoother suspension performance.
Large "wrap-around" plastic fork protectors provide excellent lower fork tube protection. The "self-supporting" design reduces friction for smoother fork operation.
Monocross link rear suspension system features a fully adjustable Kayaba, piggyback shock which provides 315mm (12.4") of wheel travel and features separate adjusters for high- and low-speed compression damping. The shock is now in-line with the center axis of the bike for excellent control. Adjustments include: spring preload, 30-way rebound damping, 20-way low-speed compression damping and 2 turns of high speed compression damping.
The shock uses an 18mm diameter piston rod. Kashima coating is used in the shock body and sub tank to reduce friction and improve suspension performance during a long moto. The Kayaba shock utilizes a full rebound oil lock system for excellent suspension function and great ride quality. The shock spring location is 30mm lower than last year, reducing the centre of gravity.
250mm floating front wave-style disc reduces weight, improves cooling and adds style too. The disc is squeezed by a Nissin twin piston caliper fitted with lightweight aluminium pistons.
"Shorty style" adjustable front brake lever can be adjusted to fit various hand sizes.
Adjustable clutch lever can be adjusted to fit various hand sizes.
245mm rear disc brake features a "wave-type" disc. The rear disc is squeezed by a single Nissin piston caliper.
Lightweight, compact, integrated Nissin rear master cylinder (fluid reservoir is integrated into the top of the master cylinder) provides strong stopping power with excellent feel and control.
The rear caliper and the lower portion of the wave disc are protected by heavy duty plastic protectors.
Compact body work includes front number plate, front fender, rad shrouds, fuel tank, side panels and rear fender which enhance the lightweight feel and look of the YZ450F. This "minimal design" bodywork is a flat design, allowing for fast, easy rider movements. The ergonomics provide a natural and roomy riding position. The body has been designed to maintain it good looks throughout the life of the machine.
Revised. lightweight, plastic resin 6.2 litre fuel tank is located mostly under the seat, once again reducing the centre of gravity and centralizes mass for exceptional handling performance.
Lightweight Sun Star rear sprocket.
Lightweight, 21" front and 19" rear Excel rims provide exceptional durability and help reduce unsprung weight for optimal suspension performance and handling.
Large 25mm rear axle and a hub design which features a second bearing on the sprocket side for increased rigidity.

Polypropylene engine and water pump guards reduce weight.
Lightweight, extra wide foot pegs provide excellent grip and ground clearance.
Folding shift lever tip helps prevent damage.
Stainless steel, inner clutch cable provides excellent strength and long life.
Lightweight chain guide / support helps reduce chance of chain derailment. Also helps protect rear sprocket damage too.
Heavy duty rubber swingarm protector
Heavy duty DID 520 drive chain
Convenient oil level sight glass

Yamaha YZ 450F Specification:

Engine
4-stroke, liquid-cooled, DOHC, 4-valve, single

Displacement
449.7 cc

Bore and Stroke
97 x 60.8 mm

Compression Ratio
12.5:1

Fuel Delivery
Keihin 44mm throttle body F.I.

Lubrication
Dry sump

Ignition / Starting
TCI / kick

Transmission
5-speed

Final Drive
Chain

Suspension (Front)
Adj. 48mm, inverted fork / 310mm travel

Suspension (Rear)
Fully adj. Monocross / 315mm travel

Brakes (Front)
250 mm, floating disc

Brakes (Rear)
245 mm, disc

Tires (Front)
80/100-21

Tires (Rear)
120/80-19

Length
2,193 mm (86.3")

Width
825 mm (32.5")

Height
1311 mm (51.6")

Wheelbase
1,492 mm (58.7")

Ground Clearance
383 mm (15.1")

Seat Height
999 mm (39.3")

Fuel Capacity
6.2 litres (1.4 Imp. gal.)

Wet Weight
111kg (244.2 lb)

Colour(s)
Yamaha Blue
Yamaha Black