| Component | Specification |
|---|---|
| Model Series | YP 400 Majesty (SH054) |
| Production Years | 2009–2011 |
| Engine Oil | 1.7 L (SAE 10W-30/10W-40, JASO MA/MB) |
| Tires (F/R) | 120/80-14 M/C 58S / 150/70-13 M/C 64S |
| Tire Pressure (F/R) | 2.0 bar / 2.25-2.5 bar |
| Battery | GT9B-4 |
| Spark Plug | NGK CR7E |
Engineering Highlight: The Aluminum-Steel Hybrid Chassis
A unique engineering hallmark of the SH054 generation Majesty 400 is its sophisticated frame construction. Unlike traditional underbone scooter frames, Yamaha utilized their proprietary Controlled Filling (CF) die-casting technology to create a lightweight aluminum alloy main frame mated to a steel subframe. This hybrid approach provided the SH054 with a level of torsional rigidity usually reserved for sport-touring motorcycles, significantly reducing the ‘scooter flex’ often felt during high-speed cornering or under heavy braking loads.
Technical Analysis: Performance & Handling
The SH054 iteration (2009-2011) represents the pinnacle of the 400cc single-cylinder evolution. By this stage, Yamaha had perfected the fuel injection mapping to eliminate the low-speed hesitation found in earlier 400cc units. The engine is a liquid-cooled, 4-stroke, DOHC 4-valve powerhouse that balances highway cruising capability with urban agility. The braking system on this specific model was also enhanced, featuring dual front discs that provide progressive feedback and superior heat dissipation compared to its predecessors.
Maintenance Guide
Fluid Dynamics & Lubrication
For the SH054, maintaining oil quality is critical due to the high-revving nature of the CVT-driven single. The system requires 1.7 liters of oil. While 10W-40 is the standard for temperate climates, 10W-30 is recommended for colder regions. Ensure the oil meets JASO MA or MB standards to protect the internal components, even though the clutch is a dry centrifugal type.
Tires and Contact Patch
The Majesty 400 uses a staggered wheel setup (14″ front, 13″ rear) to optimize the balance between stability and storage space. Correct inflation is vital for handling:
- Front: 2.0 bar (29 psi)
- Rear: 2.25 bar (33 psi) for solo riding; increase to 2.5 bar (36 psi) when carrying a passenger or full luggage.
Electrical System
The SH054 utilizes a GT9B-4 battery. Given the electronic fuel injection and the power requirements of the dual headlights, maintaining a healthy battery is paramount. If the scooter is stored for more than two weeks, a smart-charger is recommended to prevent voltage drops that can cause ECU errors.
Frequently Asked Questions
Q: How often should the NGK CR7E spark plug be replaced?
A: Under standard operating conditions, the spark plug should be inspected every 6,000 km and replaced every 12,000 km to ensure optimal combustion efficiency.
Q: Can I use automotive oil in the Majesty 400?
A: It is highly discouraged. Always use oil labeled with JASO MA/MB specifications to ensure the additives are compatible with the high-temperature environment of a high-displacement scooter engine.