Yamaha YZ250

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YZ250
YZ250.jpg
ManufacturerYamaha
Production1974-present
SuccessorYamaha YZ450F
ClassMotocross
Engine250 cc single-cylinder, water-cooled, two-stroke, cylinder reed
Power48.8 hp[1]
Torque32 ft·lbf[1]
Transmission5-speed
SuspensionMonoshock, 12.8 inches travel
Brakesdouble disc
TiresFront: 80/100-21-51M ; Rear: 110/90-19-62M
Wheelbase57.8 inches
DimensionsL: 85 inches
W: 32.5 inches
H: 51.2 inches
Seat height39.1 inches
Weight212 lb (96 kg) (dry)
Fuel capacity2.1 US gallons
RelatedYamaha YZ450F

The Yamaha YZ250 is a two-stroke motocross race bike made by Yamaha. The model was launched in 1974 and has been regularly updated, and is one of the only two-stroke bikes of this displacement still in production, with new releases every year.

Engine[edit]

The original YZ250 of 1974 used an air-cooled 250cc two-stroke engine of 70 mm bore and a 64 mm stroke, which was improved semi-annually. The air-cooled motor was replaced in 1982 with a 249 cc liquid-cooled two-stroke reed-valved engine with a YPVS exhaust valve for a wider spread of power. The bore on the water-cooled engine was reduced to 68 mm and the stroke was increased to 68 mm producing a displacement of 247 cc. In 1999, the bore was further reduced to 66.4 mm and the stroke lengthened to 72 mm producing a displacement of 249 cc. The longer stroke engine resulted in a lower redline, slightly less top end power and greatly improved torque at lower RPM.The engine produces a peak 48.8 horsepower (36.4 kW) at 8,800 rpm and 30.6 foot-pounds force (41.5 N⋅m) of torque at 7,500 rpm, with a 9,000 rpm redline [2].

Chassis[edit]

On its introduction in 1974, the YZ250 used a single backbone steel frame with a twin-shock swingarm. The following year, reflecting the factory racer Hakan Andersson's factory racer, the swingarm became a monoshock unit, initially made of steel, then aluminum from 1978. The swingarm rear suspension system featured more than 12" of travel, while the telescopic inverted front forks had 11.8 inches (300 mm) of travel.[3] In the 2005 model year the YZ250 gained a new frame made from aluminum that reduced the dry weight to approximately 212 lb (96 kg). All YZ250s feature front and rear hydraulic disc brakes.

Significant advances[edit]

2005 Aluminium frame
2006 KYB SSS forks

Advances[edit]

1999 First year of the current engine
2002 First year of the current frame geometry and bodywork
2003 Exhaust port raised about 0.5mm and h-igher compression head for USA model.
2005 Aluminium frame
2006 KYB SSS forks
2007 Pro Taper 1-1/8 Handlebars
2008 Smaller fork lugs and shorter lower tubes. Brake calipers also reduced in size + wave rotors
2011 No more US model: Bigger silencer and a neutral switch for sound checks. Low compression head.
2015 New body work (compatible with 2002 - 2014 bikes) Smaller fork tubes (at top clamp) from the four stroke.

Championships[edit]

The YZ250 holds many championships:

  • 5 AMA National Motocross Titles.[4]
  • 9 AMA National Supercross Titles[4]
  • Most recently, Chad Reed rode the YZ250 to an AMA National Supercross title in 2004.[5]
  • 6-time AMA National Offroad Championships under the hands of Jason Raines. [6]
  • In 2014 Lewis Gregory rode the GL12 Racing YZ250 Yamaha to third in the newly formed EMX300 Championship. Winning the round at the Spanish GP on the way.

See also[edit]

References[edit]