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What’s new on KTM’s 2019 two-strokes

KTM 125 SX

The powerful KTM 125 SX has been the market leader in this segment for many years now. And there is good reason for this – with a completely new chassis and power delivered by a lightweight high-performance 2-stroke engine with

a power valve and 6-speed transmission, the KTM 125 SX is the first choice for young champions and in model year 2019 will again define the benchmark in the 2-stroke segment to 125cc.


The bike’s tried and tested crankshaft has a stroke of 54.5 mm featuring an excellent balancing which reduces vibrations to a minimum. It is possible to increase the displacement of the latest engine generation to 144cc by a replacing the cylinder, piston and cylinder head without changing the crankshaft.

Smoker fans aren’t left out


A newly designed header and a new silencer are key features of the KTM 125 SX exhaust system for model year 2019. The header using the latest 3D stamping technology has been given an optimized shape and, in conjunction with the upgraded silencer internals, results in a fat torque curve and increased power delivery. A welded aluminum bracket replaces the previous plastic collars used to secure the silencer and also helps to reduce weight.


The newly developed DS (diaphragm steel) clutch features a one-piece outer clutch hub combined with a primary gear made of high strength billet steel. This guarantees unbeatable reliability and, due to its compact, rivetless construction, reduces the engine width by 10 mm. Incorporating thin steel carrier friction discs, the extremely heat-resistant clutch plates ensure reliable disengagement of the clutch. An additional benefit is that they are pre-tensioned by means of a specially designed diaphragm spring, which significantly reduces the force required to pull the clutch lever. The Brembo hydraulic system also ensures an easy and precise action.


The new and very robust 6-speed transmission unit in the KTM 125 SX has been reinforced for model year 2019 and comes from a new transmission plant operated by Pankl in Austria which represents the best there is in terms of quality and reliability. KTM has retained the gear ratios from the predecessor and matched them perfectly to the engine’s performance characteristics. All gear pairs have now been further optimized for smooth gear changes. KTM’s advanced No-Dirt technology is used for the gear shift lever and is designed to prevent mud and dirt from fouling the lever joint and thus guarantees reliable gear changing at all times.


The crankshaft of the KTM 125 SX is positioned high up in the die-cast crankcase at a point that is now closer to the center of gravity. This contributes to improved centralization of the masses and at the same time optimizes rideability. The engine unit is extremely compact and is a major factor in keeping down the overall weight of the bike. For model year 2019, KTM has reinforced the seat of the kick-starter intermediate gear for improved reliability. With a new clutch, the new clutch cover is now lower, which has reduced the engine width by 10 mm.


At the core of the engine is a compact cylinder with a 54 mm bore. Compared to the predecessor models they feature a reworked exhaust port which is now CNC milled for a more precise timing and improved interaction with the main power valve, which is made of a new raw part and machined too. Together with a twin-component cylinder head, this has resulted in outstanding engine performance and throughout the entire rpm range.


It is common knowledge that the KTM 125 SX engine is the most powerful and most competitive engine in its class. KTM is absolutely convinced that 2-stroke technology, with its outstanding power-to-weight ratio, low costs and uncomplicated engineering, will continue to lead the chase in the future. The 125cc engine was developed using the most advanced engineering expertise KTM has to offer and is the most powerful in this segment over the entire rpm range. Weighing in at a mere 17.2 kg, it is the lightest engine in its class. This gives the rider precisely what he wants – faster lap times as a result of the bike’s handling and outstanding overall performance.


The KTM 125 SX is fitted with a 38 mm flat slide MIKUNI carburetor, which provides a smooth and controllable power delivery over the entire rpm range and offers tremendously precise throttle response.

KTM 250 SX

KTM let its entire expertise flow into the development of the KTM 250 SX. The result is a high-performance 2-stroke engine in a state- of-the-art chassis. The 250cc engine features the best power-to-weight ratio in the world of motocross and, as a result of the outstanding performance combined with an ultra-light- weight chassis, it makes the KTM 250 SX the fastest bike in its class – on all tracks and on every terrain. An extremely serious opponent for significantly more complex 4-stroke motocross machines has emerged, with braking taken care of by the best brakes available on any motocross bike today.

The 250 SX has a new exhaust


To reduce the vibration levels, the KTM 250 SX engine has been fitted with a balancer shaft. This is primarily of benefit to the rider as this reduces stress and further increases the level of riding comfort.


The KTM 250 SX incorporates a DDS (damped diaphragm steel) clutch developed in-house by KTM with a robust outer clutch hub and extremely heat-resistant steel clutch plates. A diaphragm spring instead of conventional coil springs, which requires less effort to operate the clutch. This design also means that sufficient space is left to incorporate a damping system in the clutch hub. This increases traction and also extends the life of the clutch. It goes without saying that this hydraulically-operated Brembo clutch also means easy and precise action and virtually playful control.


The cylinder of the KTM 250 SX with a 66.4 mm bore is fitted with a sophisticated TVC power valve, featuring a machined exhaust port, which improves the power delivery once again for model year 2019. The bike’s power curve can be changed in a matter of seconds using the two power valve springs supplied, enabling the rider to optimize settings for different track conditions and to suit his own personal preferences. The lateral cylinder head brackets are now made of aluminum instead of steel. They enable the engine to be mounted more firmly to the frame to reduce vibration levels.


To make the cooling more effective, the engine is provided with an up- graded water pump case designed to optimize coolant flow.


The 38 mm flat slide carburetor provides smooth and controllable performance throughout the entire rpm range. A new setting has been matched perfectly to the newly designed air filter box and the new exhaust system. As a result, the engine’s throttle response is instanta- neous and the smooth power delivery is a dream.


The 2-stroke engine of the KTM 250 SX is regarded as the most powerful engine in its class. Fitted with a TVC (twin valve control) power valve, a balancer shaft to reduce vibrations, a 5-speed transmission and a hydraulic DDS clutch, it is setting the standards in its segment. As a result of modifications to the cylinder and exhaust system, this compact powerhouse shames the competition with outstanding performance and agility, and is the right choice for all those who love that typical 2-stroke sound and low purchasing and maintenance costs.


In model year 2019, the KTM 250 SX features a newly designed header and silencer. For the production of the exhaust pipe the latest 3D stamping technology is used. The new design increases ground clearance and with a slimmer construction contributes to the very compact layout of the entire system and in addition it increases power and performance characteristics in conjunction with the upgraded silencer internals. The somewhat reduced weight of the silencer has resulted from using an aluminum bracket instead of the previous one made of plastic.

The engine is coupled to a 5-speed transmission with gear ratios optimized specifically for motocross racing. KTM’s advanced No-Dirt technology is used for the gear shift lever to prevent mud and dirt from fouling the lever joint and thus guarantees reliable gear changing at all times.

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