Wiseco PK1589 90mm Top-End Piston Kit 9.5:1 Compression Honda TRX450

The Wiseco PK1589 is a complete forged top-end piston kit designed for the Honda TRX450 Foreman, delivering a standard 90.00mm bore with a 9.5:1 compression ratio. Whether you are rebuilding a worn top end or performing an oversize bore, this kit provides everything needed to restore or upgrade engine performance in a single package.

Kit Includes:

• 1x Forged aluminum piston (4825M) — 90.00mm bore
• 1x Dedicated ring set for maximum compression and oil control
• 1x Chrome-plated wrist pin with horizontal slot pin oiling
• 2x Circlips
• Top-end gasket set

Key Specifications:

• Bore (Standard): 90.00mm
• Bore (Actual): 90.00mm (STD oversize)
• Stroke: 68.00mm
• Displacement: 433cc
• Compression Ratio: 9.5:1
• Dome Volume: +5.0cc
• Wrist Pin: 19mm

Wiseco Forged Advantage:

• Forged from high-silicon, low-expansion aerospace-grade aluminum for superior strength-to-weight ratio
• CNC diamond-turned finish ensures precise sizing with no variation
• Dome design engineered for improved flame travel and resistance to detonation and pre-ignition
• Pressure seal groove for maximum ring seal
• Scuff-resistant skirt design reduces friction for longer service life
• Race-proven design chosen by top powersports race teams
• Engineered, forged, and machined in the USA in Mentor, OH

Wiseco is the only aftermarket piston manufacturer in the United States that produces pistons exclusively using the forging process, allowing full in-house control over every stage of manufacturing — from raw material to finished, skirt-coated parts. The PK1589 kit exceeds OEM sealing standards and is built to handle the demands of both recreational riding and high-performance competition use.