Wiseco 4649M09400 Forged Piston Kit Bore CR Oversize - 94.00mm 12.5 1 YZ/WR400 2.00mm

The Wiseco 4649M09400 is a 4-stroke forged piston kit designed as a 2.00mm oversize replacement, bringing the bore to 94.00mm with a 12.5:1 compression ratio. This kit is engineered for the Yamaha YZ400F and WR400F and is a direct solution for engines requiring a bore-up or cylinder resleeve.

Wiseco pistons are forged from high-silicon, low-expansion aluminum alloy, delivering superior strength, reduced reciprocating weight, improved heat transfer, and extended service life compared to cast alternatives. Each piston features a diamond-turned CNC finish for precise sizing with no variation, ensuring proper fit and ring seal across all cylinder bore compositions including cast iron, chrome, Nikasil, and boron composite.

Kit Specifications:

• Bore size: 94.00mm
• Oversize: +2.00mm over standard
• Compression ratio: 12.5:1
• Stroke: 60.1mm
• Ring set cross-reference: 3701XR
• Construction: Forged high-silicon aluminum alloy
• Finish: CNC diamond-turned for precise tolerances
• Compatible cylinder bore types: Cast iron, chrome, Nikasil, boron composite

Kit Includes:

• Forged piston
• Piston rings
• Wrist pin
• Circlips

Important Notes:

• Only Wiseco replacement ring sets (cross-ref: 3701XR) are compatible with this piston
• Nikasil or chrome bore cylinders require resleeving or replating to accept this oversize piston
• California Residents: Proposition 65 Warning — Cancer and reproductive harm. See P65Warnings.ca.gov

Wiseco has been a trusted name in performance engine components for over 75 years, with a proven track record across Supercross, Motocross, GNCC, WORCS, and other professional racing series worldwide.