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Start ShoppingAthena Big Bore Cylinder Kit for Yamaha 250F - 250cc to 290cc Off-Road Racing Upgrade
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Description
Take your Yamaha 250F's performance to new heights with Athena's premium Big Bore Cylinder Kit. This complete top-end upgrade increases displacement from 250cc to 290cc, delivering unmatched power for aggressive off-road riding and competitive racing. Engineered for durability and performance, this kit includes all essential components for a reliable, high-output big bore conversion.
Key Features
- Nickel–Silicon Carbide Plated Cylinder: Advanced coating resists heat and wear for long-lasting performance in extreme conditions
- Forged Piston: High-strength aluminum alloy construction ensures optimal power delivery and durability under stress
- High-Quality Piston Rings: Precision-engineered rings provide superior sealing for maximum compression and efficiency
- Reinforced Piston Pin & Clips: Durable components withstand high RPMs and extreme off-road conditions
- Complete Top-End Gasket Set: Ensures perfect sealing and compatibility with OEM crankshaft and connecting rod
Why Choose This Product
Upgrade to a 290cc displacement engine for noticeable power gains without compromising reliability. This all-inclusive kit simplifies installation by reusing your OEM crankshaft and connecting rod, saving time and costs. The advanced materials and precision engineering deliver consistent performance across demanding off-road terrain and racing tracks. Perfect for riders seeking a competitive edge in big-bore conversions.
SKU:
GM7080A55C
MPN:
P400485100012
UPC:
8055681300903
Category:
Piston kits & Components
Brand:
Athena
Stock:
In Stock
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Take your Yamaha 250F's performance to new heights with Athena's premium Big Bore Cylinder Kit. This complete top-end upgrade increases displacement from 250cc to 290cc, delivering unmatched power for aggressive off-road riding and competitive racing. Engineered for durability and performance, this kit includes all essential components for a reliable, high-output big bore conversion.
Key Features
- Nickel–Silicon Carbide Plated Cylinder: Advanced coating resists heat and wear for long-lasting performance in extreme conditions
- Forged Piston: High-strength aluminum alloy construction ensures optimal power delivery and durability under stress
- High-Quality Piston Rings: Precision-engineered rings provide superior sealing for maximum compression and efficiency
- Reinforced Piston Pin & Clips: Durable components withstand high RPMs and extreme off-road conditions
- Complete Top-End Gasket Set: Ensures perfect sealing and compatibility with OEM crankshaft and connecting rod
Why Choose This Product
Upgrade to a 290cc displacement engine for noticeable power gains without compromising reliability. This all-inclusive kit simplifies installation by reusing your OEM crankshaft and connecting rod, saving time and costs. The advanced materials and precision engineering deliver consistent performance across demanding off-road terrain and racing tracks. Perfect for riders seeking a competitive edge in big-bore conversions.| SKU | GM7080A55C |
|---|---|
| MPN | P400485100012 |
| UPC/GTIN | 8055681300903 |
| Brand | Athena |
| Category | Piston kits & Components |
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Featured Review
| Make | Model | Years |
|---|---|---|
| Yamaha | YZ250F | 2001-2012 |
| Yamaha | WR250F | 2001-2012 |
Frequently Asked Questions
This specific kit is designed for Yamaha YZ250F models from 2001–2012; check your exact year and confirm model against the fitment list above before ordering.[1]
Yes, the Athena 290cc big bore kit is designed to work with the stock crankshaft and connecting rod on compatible YZ250F/WR250F models; no stroke change is required.[1]
Fueling changes are strongly recommended; for carbureted models you typically need richer jetting, and for EFI models you should use an appropriate remap or fuel controller to match the increased displacement.
No cylinder boring is needed; the included Athena cylinder is a bolt‑on replacement. Normal top‑end engine disassembly and reassembly is required but no crankcase machining is typically necessary.[1]
The P400485100012 kit includes the required top‑end gaskets for cylinder and head installation, so you usually do not need to purchase a separate top‑end gasket kit.[1]
Installation Guide
Difficulty
Medium
Est. Time
3 hr 0 min
Tools Required
- Metric socket set
- Metric combination wrenches
- Torque wrench (Nm scale)
- Feeler gauges
- Piston ring compressor or suitable ring installation tool
- Soft mallet
- Clean gasket scraper or plastic razor
- Cooling system drain pan
- Service manual for torque specs and sequences
Pro Tips
- Clean all mating surfaces thoroughly and blow out oil/coolant passages before assembly
- Oil the piston, rings, and cylinder wall lightly with clean engine oil during installation
- Rotate the engine by hand several revolutions after assembly to confirm smooth operation
- Change engine oil and filter after the initial break‑in period
- Use fresh coolant and a new spark plug when installing the big bore kit
Common Mistakes to Avoid
- Not checking piston-to-cylinder clearance and ring end gap before assembly
- Incorrect piston orientation (arrow or mark not facing exhaust/front)
- Reusing old base/head gaskets or damaged O‑rings
- Incorrect head bolt torque or tightening sequence
- Failing to properly bleed the cooling system after reassembly
- Not re-mapping or re-jetting fuel system for the increased displacement
Comparison vs Stock/OEM
Compared to the stock 250cc Yamaha cylinder and piston, this Athena kit increases displacement to approximately 290cc using an 83 mm bore, providing a noticeable gain in low‑end and midrange power for off‑road use.[1][2]
Improvements
- Increased engine displacement and torque output over OEM 250cc configuration
- New plated performance cylinder and forged piston compared with a used OEM top‑end
- Complete top‑end refresh with new gaskets and wear parts
Considerations
- Engine characteristics will change; fuel mapping/jetting must be adjusted for reliability
- May not be legal for some race classes that require stock displacement
- Slightly higher internal stresses than stock; maintenance intervals should be observed closely
Durability & Warranty
Warranty
Athena typically offers a limited manufacturer’s warranty against defects in materials and workmanship for their cylinder kits; details vary by region and seller and should be confirmed at time of purchase.[1]
Maintenance
Follow Yamaha’s standard top‑end inspection intervals for high‑performance off‑road engines; frequent oil changes, air filter maintenance, and periodic valve clearance checks are essential, especially when using a big bore kit.
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