| Specification | Value |
|---|---|
| Model / Year | Yamaha YZ 250 F (CG39C/1SMJ) / 2017 |
| Engine Oil | Yamalube 4 (10W-40) API SG JASO MA (0.73 L) |
| Spark Plug | NGK LMAR8G |
| Front Tire | 80/100-21 51M Bridgestone M403 |
| Rear Tire | 100/90-19 57M Bridgestone M404/A |
| Tire Pressure | 1.0 bar (15 psi) Front & Rear |
Engineering Highlight: The Reverse-Cylinder Revolution
The 2017 Yamaha YZ 250 F (CG39C) continues to utilize Yamaha’s groundbreaking rearward-slanted cylinder design. By positioning the intake at the front and the exhaust at the rear, Yamaha engineers achieved a near-perfect centralization of mass. This configuration allows for a symmetrical intake port that provides the straightest possible path for the fuel-air mixture, significantly enhancing volumetric efficiency and throttle response in the 250cc class.
Technical Review: Performance and Dynamics
The CG39C generation is widely regarded by MotoSpecsLab as the benchmark for quarter-liter four-stroke reliability and torque. For the 2017 model year, Yamaha refined the cylinder head and transmission, improving mid-to-high range power delivery. The chassis, a bilateral beam aluminum frame, works in tandem with the KYB® Speed-Sensitive System (SSS) forks, which remains the gold standard in motocross suspension.
Maintenance Essentials
To maintain peak performance of the high-revving DOHC engine, adherence to the following technical specifications is mandatory:
- Lubrication: Use 0.73 Liters of Yamalube 4 (10W-40). The JASO MA certification is critical to prevent clutch slippage under high-load racing conditions.
- Ignition: The NGK LMAR8G long-reach spark plug is specifically designed to dissipate heat effectively from the combustion chamber of this high-compression engine.
- Traction & Handling: The Bridgestone M403/M404 combination is optimized for intermediate terrain. Maintaining a consistent 1.0 bar (15 psi) is vital for carcass flexibility and footprint optimization.
Frequently Asked Questions
What oil should I use for my 2017 YZ250F?
We recommend Yamalube 4 (10W-40) API SG JASO MA. The engine requires exactly 0.73 liters for a standard oil change.
What is the correct tire pressure for motocross use?
For the Bridgestone M403/M404 set, the factory recommended pressure is 1.0 bar (approximately 15 psi) for both front and rear tires to ensure maximum grip.
Does the 2017 YZ250F have a battery?
The 2017 CG39C/1SMJ model is a kick-start only machine and does not come equipped with an onboard battery for starting.