| Component | Specification |
|---|---|
| Model Code | CE16C / 1SR6 (2015) |
| Engine Type | 124cc Liquid-cooled 2-stroke |
| Transmission Oil | 0.66 L (Yamalube 4 10W-30 / SAE 10W-30 Type SE) |
| Spark Plug | NGK BR9EG |
| Front Tire | 80/100-21 51M (1.0 bar / 15 psi) |
| Rear Tire | 100/90-19 57M (1.0 bar / 15 psi) |
| Battery | None (Kickstart Only) |
The 2015 Yamaha YZ 125 (CE16C/1SR6) represents a pivotal moment in the history of the world’s longest-running production motocross bike. While the internal engine architecture remained largely unchanged from the previous decade—a testament to its near-perfect design—the 2015 model introduced a significant visual and ergonomic overhaul. This was the year Yamaha finally updated the plastics and styling to match the modern ‘arrow’ design of the YZ-F four-stroke line, breathing new life into the 2-stroke platform.
Engineering Highlight: The KYB SSS Dominance
The defining technical feature of the 1SR6 is the Kayaba (KYB) Speed Sensitive System (SSS) suspension. Even years after its introduction, this setup remains the industry benchmark for coil-spring forks. By utilizing a piston that is sensitive to the speed of the stroke rather than just the position, the YZ 125 offers unparalleled bottoming resistance without sacrificing small-bump compliance—a critical factor for a lightweight 125cc machine that relies on carrying corner speed.
Engine and Powertrain Maintenance
The heart of the CE16C is its high-revving, liquid-cooled 124cc engine equipped with the Yamaha Power Valve System (YPVS). To maintain peak performance, the transmission requires 0.66 Liters of Yamalube 4 (10W-30). Given the high-stress environment of 2-stroke racing, frequent oil changes are mandatory to prevent clutch fade and gear wear. The ignition system relies on an NGK BR9EG plug, which should be inspected for carbon fouling after every moto to ensure crisp throttle response.
Chassis and Handling
The 2015 model continues to use the lightweight aluminum semi-double-cradle frame. Its agility is complemented by a specific tire configuration: an 80/100-21 front and a 100/90-19 rear. For optimal traction on intermediate terrain, MotoSpecsLab recommends a consistent pressure of 1.0 bar (15 psi) for both ends. This pressure provides the necessary footprint for the 125 to ‘bite’ into berms while protecting the rims from hard landings.
Maintenance Checklist for the 1SR6
- Air Filter: Clean and re-oil after every ride. The 125cc engine breathes heavily, and any debris ingestion is catastrophic.
- Piston Life: For competitive use, the top-end should be inspected every 15-20 hours.
- Drive Chain: Ensure proper tension (40-50mm of slack) to prevent binding during rear suspension compression.
- Fuel Mixture: Always use high-quality 2-stroke premix oil at a ratio of 30:1 or 32:1 with premium unleaded gasoline.