The ProX piston kit is intended to replace the piston in a Yamaha YZ 250 F engine during a top-end rebuild. Its dimensions and compression ratio are listed below to help confirm the required piston size.

Specifications

• Standard bore: 77.00 mm
• Piston size: 76.95 mm
• Actual compression ratio: 14.1:1
• Total height: 34.30 mm
• Piston pin hole diameter: 17.00 mm
• Compression height: 11.50 mm
• Boss spacing: 16.00 mm
• Piston head: flat with raised top
• Four valve pockets
• Forged piston

Cross-Reference OEM Part Numbers

• Yamaha: D05-11631-00
• PROX: 01.2437.A

Vehicle Fitments

• Yamaha YZ 250 F: 2027