- What you must remember
- Make yourYamaha YZ 250 F 2018
- The technical aspect
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For Yamaha cross country, 2018 was mainly devoted to the 450. The 2 and a half will not hold it against because it was the one that was in the spotlight last year. And the aura is intact with its reverse cylinder head engine installed last year. This revolutionary Yamaha YZ 250 F has proven to have what it takes to outperform the toughest competition. This game-rewriting cross-country bike enshrined Jeremy Martin as the winner of the AMA 250 motocross championship for two consecutive years in 2014 and 2015, while YZ 250 F rider Cooper Webb also won the AMA 250SX West twice in 2015 and 2016.
YZ 250 F: more robust, faster and more flexible
For the 2017-2018 model year, the YZ 250 F benefits from a whole series of important technical modifications, including its all-new inverted cylinder head, which aim to increase performance while improving the handling of the two-wheeler..
Improvements on the YZ 250 F
– Increased pulling power at mid and full throttle
– Improved acceleration
– Smoother shifting and smoother clutch feel
– Refined handling and suspension provide great stability and optimized control throughout
– Improved braking power
YZ 250 F ENGINE
With improved intake and exhaust efficiency combined with a smoother gearbox and remapped ECU, the engine in this version offers a significant increase in competitiveness..
All-new cylinder head with increased performance
With its forward-facing intake and rear-facing exhaust outlet, the YZ 250 F’s state-of-the-art reverse cylinder head has many advantages over a conventional design, namely increased fuel efficiency. ‘intake and exhaust, better mass centralization through its air filter accessible from above and its fuel tank placed under the saddle. Yamaha engineers have leveraged this advanced technology tenfold and developed an inverted cylinder head that gives the YZ 250 F rider more pulling power at mid and full throttle..
Redesigned intake port and higher lift camshaft
In order to increase the flow of fresh air to the four-valve cylinder head, the position of the intake port was straightened and the diameter of the intake valve was enlarged. The arrangement of the intake and exhaust camshafts allows for increased valve lift for more thrills from mid-range. And to boost performance in low revs, the intake camshaft timing angle has been reduced..
Stronger valve springs and new connecting rod
To go along with this increased camshaft lift, more robust intake and exhaust valve springs were installed on this model. Likewise, the connecting rods have been redesigned to accompany the increased performance of the engine and it is a brand new nickel-chromium-molybdenum connecting rod that is now responsible for transmitting all this force..
Shorter intake manifold and new throttle seal
This marked increase in power in the mid and high rev ranges is also due to a shortening of the intake horn to reduce pumping losses, while the internal design of the latter promotes better fuel evaporation. In addition, the use of a larger throttle seal between the injector and the inlet port allows the cross section to be increased by 5%..
Redesigned exhaust port and new larger bore front pipe
To achieve a perfect balance between intake and exhaust, the two exhaust ports have been redesigned and the “snake” type front manifold was fitted with a larger diameter front section. Along with a larger bore, this front section also benefits from a more open bend radius which has increased the internal cross section to create a much more powerful exhaust pulsation effect..
To align with the increased engine performance achieved by this cylinder head and the renewed efficiency of the intake and exhaust systems, the YZ 250 F was matched with a redefined ECU with revised ignition timing and engine configuration. the fuel injector. The ECU triggers in high revs and includes a limiter that provides an improved over-rev feel.
Yamaha Power Tuner
Riders of all skill levels can use the optional Yamaha Power Tuner box to fine tune the power characteristics of the YZ 250 F. This compact device plugs directly into the two-wheeler without the need to carry a PC and allows the driver or mechanic to perform fine tuning of the engine in the blink of an eye to adapt its performance to the conditions of the circuit.
Very robust housings
To be able to absorb the increase in power of its engine, the YZ 250 F is equipped with much more resistant modified casings. Although their exterior shape and construction are the same as those of the versions fitted to the 2016 model, the cast aluminum housings of this model have undergone a heat treatment which has increased their strength by approximately 5%. increase their reliability and durability.
To support the optimized driving force of its ultra-powerful engine, the 2017 YZ 250 F is equipped with a new transmission with larger teeth on gears of 2 and 3 .
The shape of the 1, 3, and 5-speed claws has also been changed – along with the design of the gearshift cam, clutch lever and axle styling – for smoother shifting and faster. Finally, the even greater rigidity of the gearshift lever gives a more positive feeling when changing gears..
Main engine changes of the YZ 250 F
– High efficiency cylinder head
– Revised shape of exhaust and intake ports
– Larger intake valves
– Higher lift intake and exhaust camshafts
– Valve spring design
– Completely redesigned connecting rod
– Revised throttle seal
– Modified air filter seal design
– Wide front exhaust bore
– Remapped ECU with rev limit settings
– Very robust housings
– Redesigned clutch lever
– Redesigned gear change cam
– Redesigned gear selector
FRAME YZ 250 F
The top-mounted air filter and the fuel tank under the seat of the YZ 250 F, made possible by the use of an inverted cylinder head engine, help refocus the masses to make the two-wheeler more agile and more responsive to fly. These frame changes introduced in 2017 result in a new balance of frame stiffness, a lower center of gravity and improved suspension..
Fine-tuned aluminum frame
Thanks to feedback from its teams, Yamaha has been able to fine-tune its frame architecture to ensure that YZ 250 F riders are fully able to exploit the improved engine performance of this model. Compared to the 2016 design, the 2017-18 frame is approximately 12mm wider in the area behind the swingarm pivot point and this increased balance of stiffness ensures better handling..
Steel engine mounting brackets
The YZ 250 F offers specially designed front and top mounting brackets to complement the high torque of its 250cc engine³. With two 8mm thick steel front brackets and 6mm top brackets, the YZ 250 F’s frame provides better overall stiffness distribution for exceptional handling and ease of handling..
To leave more driving space for the rider and to accommodate as many people as possible, the footrest position of the YZ 250 F has been lowered by 5 mm. This feature helps to lower the center of gravity of the two-wheeler to increase rider control in ruts and turns..
Optimized suspension settings
The ease and comfort of driving has been perfected in the YZ 250 F thanks to several modifications to the front and rear suspensions. The unique KYB air / oil separate (AOS) fork® features a redesigned triple clamp with increased stiffness and slightly reduced oil content which, along with fine-tuned factory suspension tuning, gives the rider a better perception of frame performance and stability in ruts, bumps and the turns.
Rear disc material
For an even more powerful braking feel, the 245mm rear disc is now made from the same heat-resistant steel as the 270mm front disc and offers absolute braking confidence on the fastest circuits.
Main changes of the YZ 250 F in terms of the frame
– Refined aluminum bilateral beam frame
– Redesigned triple trees for increased rigidity
– New suspension settings
– Repositioned footrests
– Rear disc material
What you must remember
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YZ 250 F 2017
Model marketed in
The technical aspect
Yamaha YZ 250 F 2018
- Frame: aluminum double beam frame
- Tank: 7.5 liters
- Seat height: 965 mm
- Length: 2170 mm
- Width: 825 mm
- Height: 1,280 mm
- Wheelbase: 1475 mm
- Weight in running order: 105 kg
- Train before
- Telehydraulic inverted fork Ø 48 mm, deb: 310 mm
- 1 disc Ø 270, 2 piston caliper
- Front wheel:
- 5-speed gearbox
- secondary by chain
- Rear axle
- Mono-shock absorber, deb: 315 mm
- 1 disc Ø 245 mm, 1 piston caliper
- Rear wheel:
- Single cylinder
in-line, reverse cylinder head
, 4 stroke
- Cooling: by water
- Injection Ø nc
- 2 ACT
- 4 valves
(77 x 53.6 mm)
- Compression: 13.5: 1
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