YP100 Flywheel Rotor

🔄 Yamaha 100 Rotor Assembly

📦 Part Number: MIYP100-5039

⚙️ Replacement Flywheel Rotor · GY6 4-Stroke Engine · 8-Pole

📍 Installation Position: Left Side of Crank Shaft · Inside Magneto Cover

✅ 8-Pole Design · Strong Magnets · Precision Balanced · Direct Replacement

This product is a Yamaha 100 Rotor Assembly (Flywheel Rotor), part number MIYP100-5039. It is a replacement 8-pole flywheel rotor designed for GY6 4-stroke engines and is the rotating component of the magneto system.

The rotor (flywheel) mounts on the left side of the crankshaft and works together with the stator. The permanent magnets on the rotor cut through the stator coils as it rotates, generating AC power for the vehicle's electrical system and providing trigger signals for the ignition system. Weak magnetization can cause faulty running, and damaged rotors can cause severe engine damage and noise. This rotor features an 8-pole design with high-strength permanent magnets and precision dynamic balancing, providing a perfect replacement to restore proper magneto system function.

🔧 Mechanics Note:
8-pole stator/rotor will work on any GY6 50cc 137QMB as long as you have a matching 8-pole flywheel rotor to go with it and have 4/5 wires. When you order a stator generator, be sure it matches the number of poles your rotor was made for. And in reverse, if you order a flywheel rotor, be sure it matches the number of poles on your stator. If you need both, order a matching 8-pole stator generator and flywheel rotor.

• 🧲 Strong Magnets: High-performance permanent magnet material provides strong, stable magnetic force for ample charging output and reliable ignition signals.
• ⚖️ Precision Balanced: Each rotor undergoes dynamic balancing for smooth operation, reducing engine vibration and noise.
• 🔩 Precision-Machined Taper Bore: High-precision taper bore ensures tight fit with the crankshaft taper for reliable torque transfer.
• 🛡️ Accurate Trigger Block: Trigger block position and angle are precisely set for accurate ignition timing.
• 🔄 Direct Replacement: Mounting dimensions match OEM exactly — installs without any modifications.

✅ Typical Signs That Rotor Replacement Is Needed:
• Weak magnetization — noticeably reduced magnetic pull when turning the flywheel by hand.
• Insufficient charging — battery frequently loses power, headlight dim.
• Hard starting or stalling while riding — unstable ignition signals.
• Unusual metallic scraping or clicking noises during engine operation (may indicate loose or detached magnets).
• Worn keyway — causing ignition timing drift and power loss.
A rotor with weak or damaged magnets will severely affect the charging and ignition systems — failure to replace it promptly may cause serious engine damage.

✅ Installation Tips:
1. Disconnect the battery negative terminal before removal and mark the trigger block position relative to the sensor.
2. Use a proper puller to remove the old flywheel — never strike it with a hammer.
3. Clean the crankshaft taper and keyway to remove oil residue and burrs.
4. Align the keyway when installing the new flywheel — use a proper installation tool and avoid forcing it.
5. Tighten the retaining nut to OEM torque specifications.
6. After installation, rotate the crankshaft and check the gap between the trigger block and sensor (typically 0.3-0.5mm).
Professional installation by a qualified technician is strongly recommended. Improper installation may cause flywheel damage or incorrect ignition timing.

⚠️ Important Notice: This product is a Yamaha 100 Rotor Assembly, part number MIYP100-5039. This is an 8-pole design and MUST be used with a matching 8-pole stator. Rotor specifications may vary across different model years and engine displacements. Before purchase, please confirm your original stator pole count and rotor specifications. If you need to replace both the stator and rotor, we recommend ordering a matching 8-pole stator + rotor set to ensure compatibility. Images are for reference only; actual product may vary.