| Specification | Value |
|---|---|
| Model Series | CG39C / 1SMN |
| Production Years | 2014-2018 |
| Engine Oil | Yamalube 4 (10W-40) API SG/JASO MA (0.73 L) |
| Front Tire | 80/100-21 51M |
| Rear Tire | 100/90-19 57M |
| Tire Pressure | F: 1.0 bar (15 psi) / R: 1.0 bar (15 psi) |
| Spark Plug | NGK LMAR8G |
The 2014-2018 Yamaha YZ 250 F represents a pivotal moment in motocross engineering. While competitors were refining traditional layouts, Yamaha introduced the revolutionary rearward-slanted cylinder and front-intake design. This architectural shift moved the airbox to the front and the fuel tank lower, significantly centralizing mass and improving the bike’s flickability in corners—a design philosophy that continues to dominate Yamaha’s off-road DNA today.
Engineering Highlights & Engine Performance
The CG39C powerplant is a liquid-cooled, 4-stroke, DOHC, 4-valve engine. By reversing the cylinder head, Yamaha achieved a straight intake path, maximizing volumetric efficiency. For the 2014-2018 production run, the fuel injection system was meticulously tuned to provide a linear yet aggressive power delivery, making it a favorite among both amateur and professional riders.
Maintenance Essentials
To maintain peak performance, the YZ 250 F requires strict adherence to its service schedule. The engine uses a relatively small oil volume of 0.73 Liters, which means the lubricant undergoes significant thermal stress. We recommend using Yamalube 4 (10W-40) to ensure the wet clutch and high-revving internals remain protected. The use of the NGK LMAR8G spark plug is critical; its specific heat range and reach are designed to handle the combustion pressures of this high-compression engine.
Chassis and Handling
Equipped with industry-leading KYB SSS (Speed Sensitive System) forks, the CG39C offers unparalleled damping consistency. Tire selection is vital for translating power to the dirt. The standard configuration utilizes an 80/100-21 front and a 100/90-19 rear. For optimal traction and carcass flexibility, maintain a pressure of 1.0 bar (15 psi) in both tires, adjusting slightly based on track conditions (loam vs. hardpack).
Editorial Verdict
The Yamaha YZ 250 F (2014-2018) remains a benchmark in the 250cc class. Its robust build quality and innovative engine layout provide a unique riding experience. While the airbox noise can be prominent due to its forward location, the performance gains in mass centralization far outweigh the acoustic trade-off. It is a machine designed for those who value technical precision and aggressive handling.
Frequently Asked Questions
Q: How often should I change the oil?
A: Given the 0.73L capacity, we recommend oil changes every 3-5 hours of competitive riding or 7-10 hours of recreational use.
Q: Can I use a different spark plug?
A: It is highly advised to stick with the NGK LMAR8G to avoid potential detonation or fouling issues common with incorrect heat ranges.