While the fundamental architecture of the four-valve Unicam powerplant remains the same, many details have been changed to support the broader role: the crank’s mass has been increased, resulting in 13% more inertia which, for a trail rider, equals improved torque feel and response; valve timing has been revised to give the broader, smoother spread of power and torque; the gearbox is now 6-speed, rather than 5 for longer range use on tarmac; left and right engine covers wear outer covers to reduce noise; Elsewhere, the ACG has been uprated, to provide the required electrical power for the LED lights and to maintain battery charge during lower-speed running. The battery itself is a high-volume unit (Lithium Ion) Bore and stroke are unchanged from the CRf450R, at 96mm x 62.1mm, but the piston uses 3 rings instead of 1 for greater durability. Compression ratio is 12.0:1 (compared 13.5:1).
The redesigned airbox feeds the PGM-FI, managed by a lambda sensor in the large-volume single exhaust (which replaces the ‘stubby’ dual-pipe design of the CRF450R). An Air Injection (AI) system and catalyser clean up the spent gases. The four-valve Unicam cylinder head features a finger rocker arm on the inlet valves; valve lift 7.7mm and exhaust valve lift is 6.7mm. Inlet valve diameter is 38mm. The valve springs are oval in cross section and valve angle is 9° intake/10.5° exhaust. The clutch spins 7 friction discs with a 2mm clutch plate efficiently dissipating heat; the springs generate a good, consistent connection.