OS 0.50 oversize piston kit for Honda TRX500 Foreman engines and Pioneer 500/1000 engines. This oversize bore (+0.50 mm) restore compression and horsepower lost to wear, helping the engine regain quick throttle response and steady power under load. Precision-machined to tight tolerances, it delivers a reliable seal and consistent ring wear across the listed TRX500 variants and Pioneer models. Designed as an aftermarket replacement that meets or exceeds OEM specifications, it supports dependable performance in rebuilds and routine maintenance alike. This OS kit focuses on delivering enduring reliability in the harsh conditions of trail work and farm use. By restoring lost displacement and tightening up clearance, it minimizes piston slap and power drop after extended service, making it a practical, durable choice when you’re rebuilding or refreshing an aging TRX500 or Pioneer engine. Its oversize design is intentionally chosen to reestablish optimal compression and ring seating for dependable operation under load, mile after mile.

What's Included

This piston kit includes:

• Piston
• Piston Rings
• Piston Wrist Pin
• Circlips

Not included: gaskets, seals, or additional engine hardware necessary for a full top-end rebuild.

OEM & Aftermarket Cross-Reference Information

Why Choose This Aftermarket Replacement?

• Direct-Fit Compatibility: Precisely machined to match OEM bore and pin dimensions for reliable sealing and consistent wear.
• OEM Cross-Reference: Uses the Honda OEM reference 13103-HR0-F00 as the baseline, with aftermarket cross-refs available for budget builds.
• Premium Materials: Designed from high-quality aluminum alloy to handle repeated heat cycles and heavy throws in trails and fields.
• OS 0.50 Oversize Precision: Restores lost displacement and improves low-end torque without compromising reliability.
• Engine Rebuild Ready: A practical choice for restoration projects on TRX500 Foreman and Pioneer models, delivering consistent performance post-rebuild.
• Cost-Effective Performance: Provides OEM-comparable performance at a value-conscious price point for frequent maintenance cycles.

Why Upgrade?

Running a worn-out piston kit in these engines can lead to reduced compression, noticeable power loss, increased oil consumption, and the risk of piston seizure under heavy loads. Replacing with this OS 0.50 piston kit restores displacement, rebuilds compression, and returns consistent power delivery, improving reliability for demanding trail work or farm tasks.

Fitment

Specifications

Installation Notes

• Thoroughly measure bore diameter and roundness before installation; oversize kits require proper honing to achieve a true 92.50 mm bore.
• Always verify end-gap on rings and install them in the correct orientation for optimal seal and longevity.
• Lubricate piston rings, wrist pin, and bearing surfaces with light engine oil or assembly lube before assembly.
• Ensure the wrist pin is seated securely with retaining clips on both sides if required by your engine variant.
• Clean all components and mating surfaces; remove any debris from the cylinder and ring grooves to prevent scoring.
• Follow the service manual for exact torque specs and sequence when reassembling the top end and any related components.