01. Engine & Exhaust

Engine
The pure exhilaration that this bike's engine delivers warranted continued production. As it shares many of its key components with the class-leading 125, the cylinder, cylinder head and piston unit can now also be fitted on a 125 cc engine base, converting it to a 150 SX without having to replace the crankshaft. Compact and powerful, this innovative 2-stroke engine is a lightweight powerhouse that just makes perfect sense.


Cylinder
At the heart of the 150 cc engine is a 58 mm bore cylinder. It features an innovative power valve unit with a sophisticated mechanism designed for the lateral support exhaust ports. The exhaust port layout enhances engine performance, while the precise machining of the upper contour of the exhaust port ensures accurate port timing. The two component cylinder head works in complete harmony with the cylinder to deliver outstanding performance across the entire rev range.


Crankcases and engine covers
The lightweight engine cases are manufactured using a high pressure die-cast production process, keeping wall thickness to a minimum while retaining strength and durability. The design allows for a high crankshaft position which is located near to the center of gravity, resulting in optimal mass centralization and easier rideability. The engine body is extremely compact, which contributes significantly to the low engine weight. Additionally for 2020, the kickstart intermediate gear has been reworked for improved reliability.


Transmission
The KTM 150 SX is fitted with a robust 6-speed transmission. The gear ratios, which featured improvements and reinforcements, were carried over from the predecessor. The gearbox features a new drive shaft which uses a screw for pinion fixation and diaphragm spring instead of a circlip, ensuring secure pinion fixation. Another highlight of the 125 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.


Carburetor
The KTM 150 SX is fitted with a MIKUNI TMX 38 mm flat slide carburetor featuring settings that were adapted to suit the new airbox developed in 2019. For 2020, reworked reeds for intake reed block provide further improvements in function, sealing and reliability, ensuring the whole system is always providing smooth, controllable power throughout the rev range.


Crankshaft
The crankshaft has a 72 mm stroke that produces the optimal torque and revs. It has been ideally balanced and with the counter balancer shaft, results in minimum vibration. The crankshaft is placed in the perfect position to centralize mass, contributing to better agility and handling.


Cooling
Maintaining the optimal engine temperature is crucial to ensuring consistent horsepower throughout the ride. The KTM 150 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.


Exhaust
When it comes to power delivery and performance, the exhaust developed specifically for this bike plays a key role and packs a punch that is hard to beat. In addition, its special shape provides slimmer ergonomics while still operating safely within the noise limits for racing.
