Restore power and reliability to your Honda TRX450 with the OS 1.50 Piston Kit. Engineered for the 1998–2004 TRX450S Sportrax and the Foreman 4x4 family (S/ES/FE/FM), this oversize kit brings worn bores back to optimal clearance for crisp combustion and lasting durability. The kit includes a forged aluminum piston, complete ring set, wrist pin, and circlips to deliver a dependable top-end rebuild that feels like new power on demanding trail or farm runs. The +1.50 mm oversize is designed to restore compression when cylinders show bore wear, ensuring consistent performance under load.

Designed for rugged in-field use, this aftermarket replacement leverages a forged aluminum piston to handle the heat and stress of heavy ATV use, delivering reliable power delivery during climbs, towing, or long trail days. It addresses worn rings and reduced sealing from cylinder wear, offering a cost-effective alternative to OEM replacements while preserving OEM-like performance and clearances for durable, predictable operation. Perfect for trail riders and farm work alike, it’s built to endure harsh conditions where a worn piston would otherwise sap performance and reliability.

Comprehensive Vehicle Fitment

Product Specifications

OEM & Aftermarket Cross-Reference Information

What's Included

Each box contains the components below to complete a precise top-end rebuild.

• Piston
• Rings
• Wrist Pin
• Circlips

Note: Gaskets, seals, and other cylinder head components are not included in this kit.

Why Choose This Aftermarket Replacement?

• Direct-Fit Compatibility: Specifically engineered to match the bore and clearance requirements of 1998–2004 Honda TRX450S/ES/FE/FM engines for a clean, reliable install.
• OEM Cross-Reference Availability: Clear cross-reference numbers help you verify compatibility with OEM setups and alternate aftermarkets.
• Premium Materials: Forged aluminum piston delivers strength and durability under heavy-use ATV conditions.
• Performance Restoration: Restores original compression and sealing, reclaiming lost power from cylinder wear.
• Cost-Effective Reliability: A practical upgrade that sidesteps OEM price spikes while maintaining factory-like performance.
• All-In-One Rebuild Package: Includes piston, rings, wrist pin, and circlips for a complete top-end refresh.

Installation Notes:

• Verify cylinder bore size before ordering; oversize +1.50 mm requires a corresponding bore rework to 91.50 mm for proper fit.
• Measure and confirm piston orientation markings (arrow) align with the engine’s forward direction during assembly.
• Use appropriate engine assembly lube on the piston skirts and rings to prevent dry start and scuffing.
• Inspect the cylinder for wear or scoring; de-glaze or re-bore as needed to achieve true roundness and crosshatch finish.
• Install the piston rings with correct orientation and staggered gaps; ensure ring end gaps do not align across the engine.
• Install the wrist pin and secure with the circlips, confirming proper retention before final assembly and torque procedures for surrounding components (cylinder head, crankcases, etc.).

Why Upgrade?

A worn piston loses compression and power, increases blow-by, and accelerates oil consumption. Upgrading to this OS 1.50 piston kit restores proper sealing and combustion clearance, delivering reliable performance across rugged trails or demanding farm work while protecting the engine from further bore damage.