Wiseco PK1431 Forged Top End Piston Kit CR - YFM660 100.00mm 9.9 1

The Wiseco PK1431 is a complete forged top end piston kit designed for the Yamaha YFM660 at a standard 100.00mm bore and 9.9:1 compression ratio. Engineered, forged, and machined in the USA, this kit delivers the strength, precision, and reliability demanded by both serious trail riders and performance-focused builds.

Wiseco's dedicated forgings are manufactured from high-silicon, low-expansion aerospace-grade aluminum alloy, offering a superior strength-to-weight ratio compared to cast alternatives. Each piston undergoes CNC diamond-turned finishing to ensure tight tolerances and consistent sizing across every unit.

Kit Includes:

• Forged aluminum piston — aerospace alloy construction with dedicated forging for optimal cam shape and profile
• High-performance piston ring set — Wiseco-specific rings engineered for extended service life and sustained power output; note that Wiseco rings are not interchangeable with other brands
• Alloy wrist pin — precision-machined for consistent fit and reduced friction
• Circlips — wrist pin retention hardware included
• Top end gasket kit — premium materials exceeding OEM sealing standards

Important Notes:

• Wiseco pistons must be used with Wiseco rings only — ring types are not interchangeable
• Cylinder sleeve is not included and must be purchased separately
• Forging part number: 4966M

Whether you're performing a routine top end rebuild or upgrading for improved performance, the Wiseco PK1431 provides a race-proven solution with OEM-surpassing quality for the Yamaha YFM660 platform.