Strategic model of the cross range, the two and a half SX-F is back in 2019 at the top of its form. With its many innovations, the KTM 250 SX-F is once again called upon to reign supreme on the motocross tracks. Not content with being one of the lightest in its category, it offers unrivaled power deployment, but perfectly controllable. This is the reason why it appeals to both amateurs and professionals. The secret to a good engine is its ability to manage power with maximum efficiency. This package has serious assets in this area and will have no trouble leading you to victory.
The 250 SX-F’s engine is considered to be one of the most powerful in the MX2 class paddock. Capable of reaching 14,000 rpm without flinching and with phenomenal torque present throughout the rev range, this engine has plenty of response. Its compact architecture allows better mass centralization and exceptional road holding. Remember that it weighs only 25.9 kg, including electric starter.
The centerpiece of the compact DOHC (double overhead camshaft) engine, the new avant-garde cylinder head features two overhead camshafts responsible for actuating the titanium valves (32.5 mm intake, 26.5 mm exhaust ) using ultra-light rockers coated with a DLC coating. For 2019, the camshaft on the exhaust side benefits from a new distribution designed to better balance the deployment of power.
The crankshaft of the KTM 250 EXC-F offers greater rigidity. The big end bearing has two bearing shells force-fitted directly into the crankshaft crankpin. This design is the prerequisite for achieving extremely high speeds and unrivaled engine power of 250 cm.³. This design increases engine life and allows longer crankshaft service intervals; a benefit for the customer in terms of time, effort and costs.
Engine housings and covers
Using the high-pressure die-casting process results in a relatively compact and even lighter crankcase, while maintaining strength and durability. The design of the crankcase allowed KTM engineers to bring the shaft assemblies closer to the center of gravity, in order to better centralize the masses and enhance driving pleasure. Another interesting innovation to keep the engine as radiant as in its early days: engine crankcase covers with an elaborate surface structure, intended to reduce the wear caused by the rider’s boots.
The KTM 250 SX-F now features a new, more robust 5-speed gearbox. The transmission ratios of the previous version have been renewed, but the gears have all been improved and strengthened. Another highlight of the transmission is the “zero dirt” design of the selector. Designed on the same principle as the footrest, it prevents the accumulation of dust and allows the gearbox to remain operational in all conditions.
Keihin Electronic Fuel Injection Engine Management System features a new 44mm injection body. The unique position of the injector ensures excellent atomization of fuel and air entering the combustion chamber. The engine is all the more lively and generous when opening the throttle. For added convenience, independent adjustment mechanisms have been provided for cold start and idle. The MAP (absolute pressure sensor) probe, which has been tightly sealed, makes the system even more reliable. The purpose of the modifications to the gas cable was to simplify the routing of the cables and make them more accessible. The control unit (ECU) of the 2019 models offers new mappings adapted to the new design of the exhaust and the cylinder head, with the aim of better managing the traction control and the departure control. To deliver maximum power, it allows the characteristics of the engine to be adapted to each speed, according to the data communicated by the gear sensor engaged.
Cylinder and piston
The cylinder, with a bore of 78 mm, accommodates a forged piston of the bridge-box type of the highest quality, manufactured by CP. In addition to its extremely rigid structure, it stands out for its unique crown shape adapted to the high level of compression of the combustion chamber. The compression ratio (14.4: 1) and the reduced oscillating masses give the engine an extremely responsive character.
To compensate for the inertial force generated by the 250 SX-F, the engine is fitted with a multifunction balancer shaft. Besides its beneficial effect on the level of vibrations, the latter is also responsible for driving the timing chain and the water pump..
The new DS (Diaphragm Steel) clutch features a durable one-piece clutch housing and main gear (made of heavy-duty billet steel), providing rock-solid reliability. It has extremely heat-resistant steel motor friction discs pre-stressed by a diaphragm spring. The function of this system is to optimize the clutch and instantly transmit the available power to the rear wheel as soon as you release the clutch. This type of design has the effect of significantly reducing the force exerted on the clutch, which is even more true with the Brembo hydraulic system..
Every minute is precious in competition. The electric starter allows you to get back into the race without wasting time. The electric starter, standard on the KTM 250 SX-F, uses Mitsuba’s robust electric motor. The foolproof reliability of this device saves precious start-up time at crucial points in the race.
Handlebar mapping selector
All 4-stroke models have a handy mapping selector on the handlebars, which allows you to act on traction control and departure control and to switch between power curves (Standard Advanced). Traction control is a unique function with a new setting on the 2019 models. It guarantees more efficient traction and better control of the bike during acceleration phases, especially on demanding tracks. This function can be activated, even in full action, by means of the map selector·on the handlebars. When the engine is at idle, all you need to do is press both switches simultaneously to activate the start control as well, and thus leap out of the gate more quickly. Thanks to a new set-up, the starting control can now take advantage of the traction control to limit the wheel slip and gain traction. In addition to the standard engine modes, the mapping selector provides access to other engine modes for maximum stroke options.
Maintaining optimum engine temperature is essential to ensure consistent power delivery. The KTM 250 SX-F can count on new radiators lowered by 12 mm compared to its predecessor for this purpose. This position, perfectly suited to the design of the new spoilers, lowers the center of gravity and improves ergonomics. Thanks to computational fluid mechanics (CFD) computational simulation calculations and the clever cooling system put in place, this innovative system ensures that engine components are kept at the ideal temperature to guarantee the highest level of performance, no matter what. are the conditions. The special protections with which the radiators are fitted not only serve to protect them from projections of stones and other debris, but also to distribute the impact force of the shock around the radiators.
The new exhaust system, featured on all 4-stroke models, gives the engine a smoothness and liveliness that are hard to match. It has a new exhaust manifold (specific to the model) and a small additional chamber, that is, an evolved resonator called FDH (Flow Design Header). The silencer benefits from a new aluminum casing and a new end cap. The interior of the silencer has also been reworked. The new structure allows the exhaust to be removed without having to remove the shock absorber and facilitates access to the latter. It has another advantage from the point of ergonomics, because it refines the silhouette of the motorcycle while respecting the regulatory noise emission levels..
The KTM 250 SX-F relies on a new high-tech steel frame capable not only of optimizing the rider’s feel, but also of providing excellent feedback. The flexibility of the frame has been specially designed to increase the agility and stability of the motorcycle at high speeds and to ensure that the riding experience is as intuitive as possible..
The completely redesigned frame of the KTM 250 SX-F promotes the dynamic riding styles that are required in the MX2 class. As with the rest of the SX range, the chromium-molybdenum steel frame consists of hydroformed tubes assembled by automated welding, in order to guarantee the highest level of quality. The rigidity has been optimized to enhance handling. The excellent cohesion with the WP suspensions also offers the perfect compromise between agility and stability at high speed. With self-cleaning “zero dirt” footrests that won’t jam when pulled back into position, you are in complete control, whatever the conditions. All 4-stroke model frames feature three new brackets to make it easier to mount an optional composite skid plate (available in the KTM PowerParts accessory line). The frame of all 2019 SX models inherits a heavy-duty powder coating (similar to KTM Factory machines) and standard frame guards. The new rear buckle, made of lightweight aluminum, has been lengthened by 40mm to promote mobility in the saddle and improve the stability of the rear shell.
The new one-piece swingarm of the KTM 250 SX-F, obtained by high-pressure die-casting, has been designed to offer rock-solid resistance while keeping weight to a minimum. The additional 5mm of play in the axle housing allows the wheel to move backwards to improve stability on chaotic tracks. The chain measurement marks shown on the swingarm are visible from above, which greatly facilitates adjustments.
Equipped with ultra-light CNC machined hubs and premium Excel rims, the wheels of all SX models guarantee maximum stability despite a limited weight. The aluminum spoke heads on the 2019 models have been revised to limit the frequency at which the spokes have to be retensioned. The wheels are shod with the latest generation Dunlop Geomax MX 3S tires, to maximize power transfer to the ground and gain stability.
All full-size SX models feature the ultra-light WP AER 48 fork. The legs of this 48mm inverted air fork have different function, damping functions are right, air spring is left. The left fork leg has a dual chamber and air cartridge system to prevent pressure loss. Should the outer seal ever leak, the pressure exerted inside the inner cartridge will keep the motorcycle in its normal position. The extremely easy to adjust air spring can be adjusted to the weight of the rider using a single valve and the air pump supplied with the motorcycle. The right fork strut includes a cartridge specifically designed to meet the demands of the single damping arm design and can be adjusted to suit track conditions or rider preferences. All you have to do is turn the wheel 30 notches to the desired position (compression up and rebound down). New damping settings on 2019 models improved front axle control and feel.
State-of-the-art Brembo brakes are standard equipment on KTM motocross bikes. Combined with Wave brake discs renowned for their lightness, they provide the braking power expected by the most daring riders.
All models in the SX range feature a new, ultra-light polyethylene fuel tank. The capacity on standard-size SX models is still 7 liters, but the shape of the tank is more ergonomic. The fuel tank cap with internal thread ensures easy and reliable closing. To ensure better reliability of the fuel pump on 4-stroke models, KTM engineers have chosen to route the hoses from the inside..
Air filter housing
The KTM 250 SX-F’s air filter housing has been completely redesigned to optimize flow dynamics. Associated with the new intake snorkels, it ensures an exceptional power deployment and level of acceleration. In addition to the obvious performance gain, the new design also serves to better protect the air filter against soiling. The rigid support for the large Twin-Air air filter has been designed to minimize installation errors. As on previous models, filter maintenance is carried out in record time and without tools, an original feature, typically KTM.
The saddle of all SX models has been redesigned to confirm the improvements made in terms of ergonomics. The saddle cover now incorporates silicone bands to optimize grip and feel. A long screw inserted on the side allows the saddle to be better fixed to the motorcycle and makes its handling easier and safer.
All full-size SX models feature the same super-strong aluminum tapered handlebar, manufactured by NEKEN. Two positions are possible for the handlebar trigger guard with shock absorber pads. right: an ODI vulcanized handle available as standard; on the left: an ODI lock-on handle as comfortable as it is practical, thanks to its mounting system without glue or wire. The handlebar foam has also been revised as well as the hand guard which is now much easier to put on or take off. With this handlebars, victory reaches out to the pilots.
Battery and wire harness
To start the engine every time, especially in cold weather, the starter motor of the SX-F models is powered by a new, ultra-light and more efficient 2 Ah lithium-ion battery. The voltage regulator / capacitor assembly now brings all the electrical components together under the seat, to make the system even more reliable.
Info and image credits: KTM
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250 SX-F 2018
Model marketed in
The technical aspect
2019 KTM 250 SX-F
- Tank: 7 liters
- Dry weight: 99 kg
- Train before
- secondary by chain
- Rear axle
(78 x 52.3 mm)