01. Engine & Exhaust
It took extreme levels of ingenuity to fit the race-winning formula of KTM's bigger 2-strokes into a compact 85 cc engine. The super-compact powerplant is fitted with a 6-speed gearbox and delivers class-leading power and rideability throughout the entire rev range. The powervalve plays a key role in tailoring power delivery to suit track conditions and rider ability, ensuring that the only rider surprised by the incredible performance is the competition.
The cylinder on the KTM 85 SX has a bore and stroke of 47mm and 48.95 mm respectively. It features a sophisticated power valve system, which controls both the exhaust valve and the sub exhaust ports, giving the bike excellent torque and power delivery. This translates into significant midrange performance, reducing the need to overwork the clutch in loamy or sandy conditions. An adjuster screw allows the opening time of the power valve to be adjusted to suit rider preference and track conditions.
Crankcases and engine covers
The crankcases are manufactured using a high-pressure die-cast production process, keeping wall thickness to a minimum while retaining strength and durability. The design of the cases is very compact and aims at positioning the shaft arrangements as close as possible to the center of gravity, contributing to better handling.
The KTM 85 SX features a lightweight 6-speed gearbox, engineered to take a beating. The gear ratios have been developed to perfectly match the characteristics of the engine, with easy and precise shifting allowing the rider to slot in the next gear quickly and confidently. The gearbox also features a driveshaft that uses a screw to secure the front sprocket, and a diaphragm spring instead of a circlip, to ensure the front sprocket remains firmly in place. As with all KTM SX models, the KTM 85 SX transmission has a "no-dirt" gear shifter which, like the footpeg design, prevents dirt build-up.
Boasting a strong and reliable clutch with an extremely compact design, the KTM 85 SX allows riders to actuate the clutch level with ease, thanks to the FORMULA hydraulic system, which conveniently ensures that play is always compensated for. This means the clutch "bite" point remains consistent throughout the ride and under all conditions.
The KTM 85 SX features a lightweight crankshaft with optimized balancing for reduced vibration and oscillating mass. As light as the crankshaft is, the rotational inertia has not been compromised, ensuring maximum torque and revs, as well as easy rideability.
The KTM 85 SX is fitted with a race-proven MIKUNI TMX carburetor with a 38 mm flat slide. This provides buttery smooth and controllable power all the way up to the rev limiter, while the angle of the intake manifold reduces any overflow of fuel. It's also less sensitive to different altitudes and temperatures, so you can pin it wherever, whenever.
Maintaining the optimal engine temperature is crucial to ensuring consistent horsepower throughout the ride. The KTM 85 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.
The exhaust system has been designed to perfectly match the engine's power characteristics and contributes to the outstanding all-round performance and rideability. The header pipe is produced using a 3-dimensional stamping process. Once the components have been shaped, they are robot welded to ensure the highest level of quality, consistency and durability. The lightweight and compact silencer guarantees that sweet 2-stroke sound and falling safely within the noise limits for racing.