Yamaha Reveals New 2014 YZ Four-Stroke Line-Up
The 2014 YZ-F, Yamaha’s latest off-road range, comprises the YZ250F and YZ450F models. The new generation of YZ-F draws the new motorcycles closer together.
It was at the turn of the century that Yamaha first introduced the YZ400 four-stroke to the off-road scene. The combination of engine power-spread and handling was the basis for success in the first formative seasons of the MX1 and MX2 classes in the FIM Motocross World Championship. The 1999 500cc World Championship was the inaugural four-stroke FIM crown for the new era of YZ-F and was followed by eight MX1 and two MX2 World Title wins in the next 13 years. Three AMA Supercross Championships were celebrated in the mid-00s and an AMA Motocross accolade in 2007. Across the categories and in the last fifteen years Yamaha have accumulated seventeen major titles thanks to names like Bartolini, Everts, Cairoli, Philippaerts, Reed, Demaria, Campano and Fontanesi.
The YZ450F and YZ250F share the same platform and gamut of technology, each taking advantage of a rear-slanting engine layout and an exhaust pipe that flows from the back of the cylinder head. The YZ450F has been a forerunner of this design since 2009 and for 2014 the fuel injected YZ250F now draws on the matching base and potential.
Both motors are fuel injected and while the 2014 YZ250F engine shares ingredients from its ‘big brother’, the former also has specific components of its own: a new cylinder head, piston, larger intake and exhaust ports, valve mechanisms and ignition timing with a lighter crankcase; that is just one of several features that help reduce weight.
Aesthetically, the standout visual is the ‘disappearance’ of the fuel tank hub with the whole 7.5l unit buried into the machine. The seat and rear fender have been overhauled and the air scoop is a prominent feature of the motorcycles’ ‘face’ for 2014. New lines are evoked through the ‘in mould’ graphics; a technique utilised by Yamaha in which the graphic film is inserted into the injection mould before the part is cast so that graphics are morphed into the piece itself, giving it a translucent look and a surface that is more resistant to scratches and wear.
To house the engines and force the components of the bikes into a more centralised mass, a revised 250 class dimensioned chassis was called for that now features a hydro-formed bilateral beam frame with ten different types of forged, cast and extruding aluminium parts. A new thinner and trimmed radiator and shorter subframe and several lighter components contribute to the lighter feel and weight saving. The lightness has been further achieved with reduced crankcase dimensions and simplified lubrication systems with a wet sump and a compact fuel pump.
Getting ‘lower’, ‘closer’ and more ‘central’ with the mass-composition of off-road motorcycles to improve grip, feel and handling have presented interesting technical challenges to the engineering department in Iwata over the last decade.
The YZ250F and YZ450F benefit from mass centralisation aspects such as the snaking exhaust pipe layout and deeper location of the increased capacity fuel tank (bigger by over a litre) and the central placement of the fuel injection components such as the engine ECU and a new wire harness. The exhaust curvature – first introduced by the Monster Energy Yamaha Grand Prix team on Factory machine – extends length and permits an improved pulse effect and power development. This is because of the variance in the diameter of the pipe itself starting from the cylinder head all the way to the silencer. The spiralling form of the exhaust means the muffler can be shortened and pulled closer towards the middle of the bike; again assisting with mass-centralisation.