| Component | Specification |
|---|---|
| Model Series | GPD155A (SG651 Generation) |
| Production Years | 2021–Present |
| Engine Oil | SAE 10W-40, API SG+, JASO MB (0.9 L) |
| Spark Plug | NGK CPR8EA-9 |
| Battery | YTZ6V (12V, 5.0 Ah) |
| Tire Size (F/R) | 110/70-13M/C 48P / 130/70-13M/C 63P |
| Tire Pressure (F/R) | 1.5 bar (22 psi) / 2.25-2.5 bar (33-36 psi) |
Engineering Highlight: The VVA Revolution
The Yamaha N-MAX 155 (SG651) stands as a benchmark in the urban mobility segment, primarily due to its Variable Valve Actuation (VVA) system. While most small-displacement scooters sacrifice low-end torque for top-end speed, the SG651 utilizes a solenoid-actuated cam profile switch at 6,000 RPM. This allows the engine to maintain high volumetric efficiency across the entire power band, a direct trickle-down technology from Yamaha’s higher-capacity R-series sportbikes.
Technical Maintenance Deep-Dive
1. Lubrication System (JASO MB Requirement)
Unlike standard motorcycles, the N-MAX 155 utilizes a centrifugal dry clutch and a CVT transmission. Therefore, it is critical to use JASO MB rated oil. Using JASO MA/MA2 (designed for wet clutches) can lead to unnecessary friction losses and decreased fuel economy. The SG651 requires exactly 0.9 liters during a standard oil change.
2. Ignition & Electrical
The NGK CPR8EA-9 spark plug is gapped specifically to work with Yamaha’s TCI (Transistor Controlled Ignition). For the electrical system, the YTZ6V battery provides the necessary cold cranking amps (CCA) to support the Smart Key System and the Start & Stop System (SSS) without parasitic drain issues common in older generations.
3. Chassis and Contact Patch
Equipped with 13-inch wheels, the SG651 offers a balance between agility and stability. Maintaining the precise tire pressure of 1.5 bar (22 psi) in the front is vital for steering feedback, while the rear pressure should be adjusted to 2.5 bar (36 psi) when operating under maximum load to prevent sidewall deformation and overheating.
Editor’s Verdict
The SG651 revision of the N-MAX 155 remains the gold standard for the ‘Maxi-scooter’ sub-200cc category. Its integration of the Blue Core engine philosophy with a high-rigidity backbone frame makes it not just a commuter, but a precision-engineered tool for the modern urban environment. Regular adherence to the JASO MB oil standard and spark plug intervals is the key to longevity for this high-compression (11.6:1) power unit.