01. Engine & Exhaust
The engine of the KTM 250 SX features the latest 2-stroke technology, with a counter-balance shaft for low engine vibration, as well as a reliable hydraulically operated DDS clutch. It has a twin-valve controlled power valve, which contributes massively to making the KTM 250 SX engine the most competitive 2-stroke in its class. Powering through its 5-speed transmission truly is an exhilarating experience.
The cylinder on the KTM 250 SX has a bore of 66.4 mm and is fitted with a Twin-Valve powervalve system. The exhaust port is machined for precise power valve function, providing excellent overall power delivery. By using the two supplied springs, the power characteristics can be changed quickly and easily, ensuring optimal settings for different tracks and rider preference. The lateral cylinder head brackets are made of aluminum and reduce vibration to levels of near insignificance.
Crankcases and engine covers
The compact engine cases are manufactured using a high pressure die-cast production process that helps with weight reduction, while retaining strength and durability. The design allows for optimal shaft arrangements closer to the center of gravity, resulting in perfect mass centralization and easier rideability. The engine covers feature a smart surface structure that reduces wear caused by the rider's boots, keeping them looking as fresh as the day you bought it.
The engine has a strong 5-speed gearbox built to suit any kind of motocross track. The gear ratios were developed specifically to match the power delivery of the 250 cc engine. The gearbox also features a no-dirt gear shifter. Similar to the foot peg design, it prevents the build-up of dirt and ensures the next gear is always available, no matter what the conditions.
No more numb hands and feet. This engine design allows for the addition of a lateral balancer shaft, which helps keep engine vibrations to a minimum. This means you can keep charging harder for longer.
The KTM 250 SX is fitted with the extremely durable, KTM-developed DDS clutch (damped diaphragm steel), with a wear-free steel basket and heat resistant clutch plates. It uses a diaphragm spring instead of the usual coil springs, which results in considerably easier clutch action. The diaphragm spring is also compact enough to allow for a damping system to be integrated into the clutch hub, contributing to better traction and durability. Additionally, the Brembo S.p.A hydraulic system provides easy and precise clutch modulation.
The KTM 250 SX is fitted with a MIKUNI TMX carburetor that for 2021 is matched with a new throttle assembly with roller actuation. The settings on the 38 mm flat slide carburetor perfectly suit the airbox and exhaust design, providing smooth, controllable power all the way through the rev range.
All 2-stroke models feature a CDI control unit with advanced hardware that improves the starting behavior of the engine. The ignition curves remain unchanged.
At the heart of the engine, the crankshaft delivers a 72 mm stroke that produces optimal torque and revs. It is ideally balanced and with the added aid of a counter balancer shaft, minimum vibration is guaranteed. The crankshaft is situated in the perfect position to centralize mass, contributing to better agility and handling.
Maintaining the optimal engine temperature is crucial to ensuring consistent horsepower throughout the ride. The KTM 250 SX features radiators which are positioned for a lower center of gravity. Their design matches the shrouds perfectly and offers a great slim feel to the ergonomics. By using CFD technology (computational fluid dynamics) together with a clever coolant circuit routing, the innovative system ensures the optimum engine temperature for the highest performance, no matter what the conditions. The radiators also feature special protectors that serve not only as protection from flying rocks and debris but also as a brace that disperses energy around the radiators in the event of an impact.
When it comes to power delivery and performance, the exhaust plays a key role and packs a punch that is hard to beat. In addition, its narrow shape provides slimmer ergonomics while still operating safely within the noise limits for racing.