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Start ShoppingAthena Big Bore Cylinder Kit for 125cc Engine - 144cc Displacement, 14:1 Compression Ratio
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Description
Elevate your 125cc engine's performance with Athena's premium big bore cylinder kit. This high-output upgrade delivers 144cc displacement and 14:1 compression ratio for explosive power without compromising reliability.
Key Features
- Nickel–silicon-carbide coated cylinder bore: Reduces friction and wear for long-lasting durability in high-performance applications
- High-compression design: 14:1 compression ratio maximizes combustion efficiency for increased horsepower
- Complete OEM-level kit: Includes cylinder, piston, piston pin, rings, and all necessary gaskets for seamless installation
- Thermal-resistant gaskets: Engineered to withstand extreme temperatures and pressures for consistent performance
Why Choose This Product
Upgrade to Athena's in-house engineered cylinder kit for factory-level reliability. The 144cc big bore configuration delivers significant power gains while maintaining engine longevity. This comprehensive kit includes everything needed for a successful top-end rebuild, ensuring optimal performance for off-road and track use.
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Elevate your 125cc engine's performance with Athena's premium big bore cylinder kit. This high-output upgrade delivers 144cc displacement and 14:1 compression ratio for explosive power without compromising reliability.
Key Features
- Nickel–silicon-carbide coated cylinder bore: Reduces friction and wear for long-lasting durability in high-performance applications
- High-compression design: 14:1 compression ratio maximizes combustion efficiency for increased horsepower
- Complete OEM-level kit: Includes cylinder, piston, piston pin, rings, and all necessary gaskets for seamless installation
- Thermal-resistant gaskets: Engineered to withstand extreme temperatures and pressures for consistent performance
Why Choose This Product
Upgrade to Athena's in-house engineered cylinder kit for factory-level reliability. The 144cc big bore configuration delivers significant power gains while maintaining engine longevity. This comprehensive kit includes everything needed for a successful top-end rebuild, ensuring optimal performance for off-road and track use.| SKU | GM0BA58A4F |
|---|---|
| MPN | P400485100030 |
| UPC/GTIN | 8055681301023 |
| Brand | Athena |
| Category | Engine |
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Featured Review
| Make | Model | Years |
|---|---|---|
| Yamaha | YZ125 | 2005-2021 |
Frequently Asked Questions
This Athena P400485100030 cylinder kit is listed specifically for Yamaha YZ125 model years 2005–2021; always confirm against the fitment selector before purchase.[1]
This configuration is a 144cc big bore kit with a 14.0:1 compression ratio for the YZ125, designed to increase displacement and performance over stock.[1]
The kit includes a new cylinder, piston, piston pin, piston rings, and all necessary top-end gaskets required for the rebuild.[1]
For the listed YZ125 2005–2021 applications, the Athena big bore kit is intended as a bolt-on top-end replacement; no case machining is noted in the product description, but you should verify against the service manual or Athena’s documentation for your year.[1]
Many riders use premium pump fuel with similar 144cc YZ125 big-bore kits, but due to the higher compression ratio Athena and your tuner may recommend high-octane or race fuel depending on jetting, timing, altitude, and riding conditions; consult a qualified tuner.
Installation Guide
Difficulty
Medium
Est. Time
1 hr 30 min
Tools Required
- Metric socket set
- Torque wrench
- Allen/hex key set
- Feeler gauges
- Soft scraper or plastic razor for gasket surfaces
- Engine assembly lube or 2-stroke premix oil
- Service manual for torque specs
Pro Tips
- Lay out the kit and compare every gasket and part with the OEM parts being removed before teardown[1]
- Always use new coolant and fresh 2-stroke premix after a top-end change
- Lightly oil the piston, rings, and cylinder wall with quality 2-stroke oil during assembly
- Rotate engine slowly by hand after assembly to confirm free movement before first start
- Re-torque cylinder head fasteners after first full heat cycle if recommended by the service manual
Common Mistakes to Avoid
- Failing to properly clean gasket surfaces before installing new gaskets
- Not checking ring end gap and piston orientation during assembly
- Reusing old top-end gaskets instead of those supplied in the kit[1]
- Not using a torque wrench or following proper torque sequence on cylinder/head fasteners
- Skipping initial heat-cycle break-in on a new big-bore top end
Comparison vs Stock/OEM
Compared with the stock Yamaha YZ125 cylinder and piston, this Athena kit increases displacement to 144cc and uses a high-quality nickel–silicon-carbide bore coating and performance-oriented piston design.[1]
Improvements
- Increased displacement (144cc vs stock 125cc) for stronger low–mid range power and overall output[1]
- Nickel–silicon treatment enhances wear resistance and heat transfer compared to many OEM cast iron or basic plated bores[1]
- Includes all new top-end components and gaskets for a complete refresh rather than reusing worn OEM parts[1]
Considerations
- Higher compression and displacement may require jetting changes and potentially higher-octane fuel depending on tuning[1]
- Not legal for displacement-restricted 125cc classes in some racing series
- Top-end service intervals may be more frequent if used in high-level racing compared with stock
Durability & Warranty
Warranty
Standard Athena product support; specific term not listed on RevZilla product page, so buyers should verify current Athena warranty policy for cylinder kits.[1]
Maintenance
Follow OEM YZ125 top-end inspection and replacement intervals, with more frequent checks for ring wear, compression, and piston condition if used in competitive racing. Maintain correct premix ratio and jetting to prevent detonation and excessive wear.
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