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. A special manufacturing process is used and provides impressive weight savings without sacrificing strength or durability. The super compact power plant is fitted with a 6-speed gear box and delivers class-leading power and rideability throughout the entire rev range. The power valve 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 2021 model has a bore and stroke of 47/48.95 mm. 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 85 SX features a light and robust 6-speed gearbox. The gear ratios have been developed to perfectly match the characteristics of the engine, while easy and precise shifting allows the rider to select the next gear quickly and confidently. The gearbox features a new drive shaft which uses a screw for front sprocket fixation and diaphragm spring instead of a circlip, ensuring optimal front sprocket fixation. Another highlight of the 85 SX transmission is the no-dirt gear shifter. Similar to the footpeg design, it prevents the build-up of dirt and ensures the next gear is always available, no matter what the conditions.
The KTM 85 SX features a strong and reliable clutch with an extremely compact design. The clutch is easily actuated by the Formula hydraulic system, which conveniently ensures that play is always compensated for, keeping the clutch bite point the same 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.
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 has been reworked with improved packing wool (40 g lighter), guarenteeing that sweet 2-stroke sound and falling safely within the FIM noise limits.