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 still in production with new releases every year.
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-strokereed-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.[1]
ChassisEdit
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.[2] 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.
TimelineEdit
This section is in list format but may read better as prose. You can help by converting this section, if appropriate. Editing help is available.(February 2021)
1999
First year of the current engine
2002
First year of the current frame geometry and bodywork
2003
Exhaust port raised about 0.5 mm and higher compression head for USA model.
yamaha, yz250, stroke, motocross, race, bike, made, yamaha, model, launched, 1974, been, regularly, updated, still, production, with, releases, every, year, yz250manufactureryamahaproduction1974, presentsuccessoryamaha, yz450fclassmotocrossengine250, water, co. 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 still in production with new releases every year YZ250ManufacturerYamahaProduction1974 presentSuccessorYamaha YZ450FClassMotocrossEngine250 cc 15 cu in water cooled reed valve two stroke singleTransmission5 speedSuspensionMonoshock 12 8 inches travelBrakesDouble discTiresFront 80 100 21 51MRear 110 90 19 62MWheelbase1 470 mm 57 8 in DimensionsL 2 200 mm 85 in W 830 mm 32 5 in H 1 300 mm 51 2 in Seat height990 mm 39 1 in Fuel capacity7 9 L 1 7 imp gal 2 1 US gal RelatedYamaha YZ450F Contents 1 Engine 2 Chassis 3 Timeline 4 Racing 5 See also 6 ReferencesEngine EditThe 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 1 Chassis EditOn 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 2 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 Timeline EditThis section is in list format but may read better as prose You can help by converting this section if appropriate Editing help is available February 2021 1999 First year of the current engine2002 First year of the current frame geometry and bodywork2003 Exhaust port raised about 0 5 mm and higher compression head for USA model 2005 Aluminium frame2006 KYB SSS forks2007 Pro Taper 1 1 8 handlebars2008 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 Racing Edit5 AMA National Motocross Titles vague 3 9 AMA National Supercross Titles vague 3 AMA National Supercross 2004 championship by Chad Reed 4 6 time AMA National Offroad Championships by Jason Raines vague 5 See also EditYZ85 YZ125 YZ250FReferences Edit Every Champ Motocross Action Magazine motocrossactionmag com Archived from the original on 2014 06 25 2008 Yamaha YZ250 Specifications specs spec a b EVERY CHAMP Motocross Action AMAMotocross com 2004 AMA THQ Supercross Series results Raines Racing www rainesracing com nbsp Wikimedia Commons has media related to Yamaha YZ nbsp This motorcycle scooter or moped related article is a stub You can help Wikipedia by expanding it vte nbsp This Motorcycle racing related article is a stub You can help Wikipedia by expanding it vte Retrieved from https en wikipedia org w index php title Yamaha YZ250 amp oldid 1165079893, wikipedia, wiki, book, books, library,
