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Start ShoppingAthena P400485100008 Standard Bore Race Cylinder Kit for 125cc 2-Stroke Engines
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Description
Upgrade your 125cc 2-stroke engine's power and reliability with Athena's premium standard bore race cylinder kit. This complete replacement system delivers enhanced performance for track days and competitive riding while maintaining factory-like durability.
Key Features
- 54mm Standard Bore Construction: Optimized for 125cc 2-stroke engines with precise machining for maximum power output.
- Nickel-Silicon Carbide Plated Cylinder: Corrosion-resistant coating ensures long-lasting performance in harsh racing conditions.
- Complete Component Set: Includes piston, rings, pin, circlips, gasket set, and all necessary hardware for seamless installation.
- High-Grade Aluminum Alloy: Lightweight yet durable construction for improved engine efficiency and heat dissipation.
- Performance-Optimized Design: Engineered for race applications with reinforced piston and ring configurations.
Why Choose This Product
Whether you're competing in track events or pushing your 2-stroke engine to its limits, this cylinder kit offers a balanced mix of power, reliability, and ease of installation. The standard bore design maintains compatibility with existing engine components while delivering enhanced performance through precision manufacturing. The included gasket set and circlips ensure a perfect seal, reducing the risk of compression leaks. Riders will appreciate the lightweight aluminum cylinder that improves thermal efficiency without sacrificing strength, making it ideal for high-output racing scenarios.
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Upgrade your 125cc 2-stroke engine's power and reliability with Athena's premium standard bore race cylinder kit. This complete replacement system delivers enhanced performance for track days and competitive riding while maintaining factory-like durability.
Key Features
- 54mm Standard Bore Construction: Optimized for 125cc 2-stroke engines with precise machining for maximum power output.
- Nickel-Silicon Carbide Plated Cylinder: Corrosion-resistant coating ensures long-lasting performance in harsh racing conditions.
- Complete Component Set: Includes piston, rings, pin, circlips, gasket set, and all necessary hardware for seamless installation.
- High-Grade Aluminum Alloy: Lightweight yet durable construction for improved engine efficiency and heat dissipation.
- Performance-Optimized Design: Engineered for race applications with reinforced piston and ring configurations.
Why Choose This Product
Whether you're competing in track events or pushing your 2-stroke engine to its limits, this cylinder kit offers a balanced mix of power, reliability, and ease of installation. The standard bore design maintains compatibility with existing engine components while delivering enhanced performance through precision manufacturing. The included gasket set and circlips ensure a perfect seal, reducing the risk of compression leaks. Riders will appreciate the lightweight aluminum cylinder that improves thermal efficiency without sacrificing strength, making it ideal for high-output racing scenarios.| SKU | GM5A06FC62 |
|---|---|
| MPN | P400485100008 |
| Brand | Athena |
| Category | Piston kits & Components |
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Featured Review
| Make | Model | Years |
|---|---|---|
| Yamaha | YZ125 | 2005-2021 |
Frequently Asked Questions
No. It is a **standard bore 54 mm, 125cc race cylinder kit**, intended as a performance replacement for the OEM cylinder rather than a big‑bore conversion.[3]
It typically includes the plated aluminum cylinder, piston, rings, wrist pin, circlips, and a top‑end gasket set, so most of what you need for a complete top‑end refresh is included.[2]
No machining or case boring is required because this is a **standard‑bore replacement cylinder** designed to fit OEM crankcases for the listed YZ125 applications.
Many experienced home mechanics can install it with standard tools and a service manual, but precise torqueing, ring orientation, and cleanliness are critical; less‑experienced users may prefer professional installation.
Jetting may need fine‑tuning to account for the fresh top end and any other modifications; checking plug color and engine behavior and adjusting jetting accordingly is recommended.
Installation Guide
Difficulty
Medium
Est. Time
2 hr 0 min
Tools Required
- Metric socket set
- Torque wrench
- Ring compressor or careful hand installation of rings
- Feeler gauges (to check ring end gap if required)
- Plastic scraper or gasket remover
- Soft mallet
- Coolant drain pan
- Service manual for torque specs
Pro Tips
- Pre‑lube piston, rings, and cylinder wall with 2‑stroke oil during assembly
- Stuff clean rags in crankcase openings when installing circlips to prevent dropped parts
- Heat cycle the engine gently and follow a conservative break‑in procedure before racing
- Verify squish clearance and jetting after installation for optimal performance and reliability
Common Mistakes to Avoid
- Not cleaning old gasket material from cylinder and crankcase mating surfaces
- Incorrect piston ring orientation (not aligning ring end gaps with locating pins)
- Reusing old circlips instead of new ones supplied in kit
- Not torquing cylinder and head nuts to factory specification in the correct sequence
- Failing to properly bleed/ refill cooling system after installation
Comparison vs Stock/OEM
The Athena P400485100008 kit is a **standard‑bore performance replacement** for the OEM YZ125 cylinder, using a nickel–silicon carbide plated aluminum cylinder similar to OEM but often marketed as a race‑oriented option.[2][3]
Improvements
- Brand‑new cylinder replaces damaged or worn OEM cylinder without requiring re‑plating
- Complete kit with matched piston and gaskets simplifies top‑end service
- Race‑oriented porting and plating quality (per Athena’s cylinder kit line) aimed at restoring or improving performance over a tired OEM top end
Considerations
- Must be used within the specified model years and with correct jetting and break‑in
- Performance benefits over a brand‑new OEM cylinder will depend on engine setup and tuning
- Not a big‑bore; maintains 125cc displacement for class‑legal racing
Durability & Warranty
Warranty
Typical Athena cylinder kits are sold with a limited manufacturer warranty against manufacturing defects; specific terms vary by distributor and region.
Maintenance
Follow normal 2‑stroke top‑end maintenance: periodic compression checks, regular air‑filter and premix maintenance, and inspection/refresh of piston and rings at intervals appropriate for your riding style (race use requires more frequent service).
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