The CRF250L' s engine is based on a well-reputed liquid-cooled 250 cc single-cylinder DOHC engine, developed as a global engine transcending regions and known for being sporty yet eco-friendly while pointing the way to the next generation. The CRF250L version of this global engine aims for output characteristics that can be handled with ease both on and off road and deliver a fun ride. This new engine is designed to be lightweight and compact with smooth turnover, not just in the low- to mid-rpm ranges but also the high rpm range.
To give the rider easy control of the machine.even off road.while improving full traction performance, the development team pursued powerful torque with no "dip" in the low rpm range.
Furthermore, given the agile feel of a liquid-cooled DOHC engine, the model realizes the ideal response for an on/off-road model while maintaining a short stroke (bore-stroke ratio: .76 mm x 55 mm) in the base engine.
To realize output characteristics that are stress-free and smooth from low rpm to high, the CRF250L developers conducted a thorough analysis of the air intake/exhaust system, which allowed them to select the ideal dimensions for the intake/exhaust pipe diameter, pipe length, and throttle bore. Moreover, the quest for reduced air flow resistance led to an optimal shape and placement of the air cleaner element and its routes to the straight intake/exhaust ports and exhaust pipe.
Cross-sectional view of straight port
The crank journal employs a half-split, press fit metal bearing for the first time in a Honda motorcycle for the single-cylinder off-road category, while the crank bearing uses a cast-iron bush. To reduce weight and improve quietness, the design strengthens the rigidity of the case housing and controls the change in internal diameter oil clearance from thermal expansion.
In addition, vibration is reduced by adopting a primary balancer.
Cross-sectional view of crankshaft unit