2005 Honda CR125R
11/22/2004 8:36:54 PM
In the pitiless arena of motocross racing, if you're not moving forward, you're moving backwards. That's why 2005 brings a radically new CR125R from Honda, with a new engine developed to increase low-end and midrange power while maintaining the CR's superior top-end punch. The CR125R's already-excellent chassis has also received additional attention for 2005 to round out what will certainly be a class leader this season.
For starters, this new engine incorporates a completely new crankcase design aimed at improving engine breathing. But the changes run much deeper, encompassing the entire top-end: cylinder and cylinder porting, head, reed-valve induction system, exhaust valve and exhaust system.
Beginning at the start of the intake tract, the 2005 CR125R incorporates an all-new six-petal reed valve, with petals that are significantly stiffer and larger, a change that results in much quicker valve closure to ensure more efficient crankcase charging and improved off-idle throttle response. The intake tract is now smoother and more direct for improved fuel-mixture flow, and revised porting specifications yield a big increase in low-end and midrange snap. The shape of the combustion chamber and the piston dome have also been changed, resulting in a slightly lower compression ratio (8.6:1) for even greater drivability. The 54.0mm piston now features a single 7-degree keystone ring in place of the previously used straight-cut ring to enhance sealing and promote longer life.
On the exhaust side, a new RC-style exhaust valve features a special HRC rotary flap design with a mechanical governor control that provides rapid and positive actuation. As a result, the new CR125R delivers a smooth transition in power between low- and mid-range engine speeds. In addition, a redesigned exhaust valve flap features more overlap to minimize exhaust gas leakage between flap and cylinder, to optimize top-end power. A new exhaust pipe enhances low-end power, and a new expansion chamber boosts overall power output. Naturally, changes to carburetor setting and the ignition mapping accompany these changes to maximize total power output.
New dual radiators feature a deeper core (now 28mm compared 24mm) for added cooling, and a new routing path for the coolant enhances heat reduction for more consistent power. A new surface treatment for the shift fork shaft plus other changes to the shift forks and drum produce a more durable, slicker-shifting gearbox.
Returning with Honda's third-generation twin-spar aluminum frame, already lauded as the top-handling package in the class, the 2005 CR125R's rolling chassis boasts a number of refinements, including a new, lighter rear hub for less unsprung weight, and recalibrated settings in the Pro-Link rear suspension system for improved performance.
With such a wealth of improvements, the CR125R is destined to establish new standards of excellence for 125-class two-strokes in 2005.