The new 250 XC-F engine is based on the similar overall design of its predecessor, with some major refinements to make this power plant more compact and lighter, with the production of improved torque and power across the entire rpm range. Perhaps one of the most impressive benefits of the new design is a weight reduction of 2 lbs, while still including the incredibly beneficial electric starter. The reworked engine guarantees an improved power curve over the entire rev range up to 14,000 rpm, which makes the new 250 XC-F a winner for both amateur and professional riders.
The centerpiece of the compact DOHC (Double Overhead Camshaft) engine is the new cutting-edge cylinder head. It features improved combustion chamber geometry, two 150 g lighter overhead camshafts with new timing, plus a friction-optimized super-fine surface, new finger followers with a 30 % harder DLC coating and a reworked timing drive (friction reduced and shorter DID timing chain, new sprockets and chain guides). New valve springs and retainers for the four lightweight titanium valves (intake 32.5 mm, exhaust 26.5 mm) and high-flow ports create a maximized flow rate for an optimal power band and maximum performance, all the way up to a redline of 14,000 rpm.
Cylinder & piston
In the reworked and shorter cylinder that has a bore of 78 mm, is a weight-reduced, forged bridged box-type piston made by CP. It features a unique piston shape adapted to the new combustion chamber and stands out with its extra-rigid structure, combined with a low weight. The compression ratio is at 14.4:1. Thanks to the low oscillating masses, the engine offers extremely lively characteristics.
The new 250 XC-F's crankshaft features a stiffer design and employs a 6 mm shorter connecting rod, contributing to the compact and light engine with a snappy power delivery. A plain big end bearing features two force-fitted bearing shells run directly on the crank pin. This design is a major prerequisite for the extremely high engine speed levels and the unrivalled maximum power of the 250 cm³ engine. Not only that, it enhances the engine's durability, allowing long crankshaft service intervals.
Counter balancer shaft
In order to balance the mass-forces, the new 250 XC-F engine uses a multifunctional counter balance shaft that also drives the water pump and timing chain. It features new sprockets fitted to the new timing chain.
The new 250 XC-F is fitted with an electric starter as standard, which a clear advantage in the heat of battle. A new starter motor made by Mitsuba (modified for easy disassembly) and a weight-reduced starter drive guarantees more efficient and reliable starting.
Engine cases and cover
The completely new design of the die-cast engine cases allowed for a much more centralized shaft configuration. The engine is now shorter by 20 mm, contributing to a much more centralized mass. Newly designed engine covers made of magnesium feature an advanced surface structure reducing the wear caused by the rider's boots.
The highly compact CSS clutch (Coil Spring Steel) features a weight reduced, wear-free steel basket, and now seven instead of eight clutch plates, which are extremely heat resistant due to their steel carrier discs. In addition, a reworked inner hub and a pressure plate guarantees a better oil supply along with even better cooling of the clutch. A smaller master cylinder diameter of the Brembo hydraulic clutch system provides lighter pull and precise modulation.
The new engine is fitted with an all-new and weight reduced, six-speed semi-close ratio gearbox. One of the new and special features on the bike is an advanced "NO-DIRT" gear lever design, which prevents dirt from blocking the joint of the lever and guarantees a safe activation of the transmission.
Engine management system
The completely reworked Keihin Engine Management System with electronic fuel injection features an all-new 44 mm throttle body, which provides instantaneous response and maximum performance thanks to a revolutionary injector position. The new ECU (Engine Control Unit) includes a launch control for more efficient starts with the provision of different maps according to the gear sensor selection. In addition, the rider can activate an optional map for a different power delivery via the map select switch on the handlebar.