OS +0.50 mm Piston Ring Kit for the TRX300 FourTrax engine offers a precise bore-size restoration for model years 1988 through 2000. Designed to renew the piston rings to the correct 74.50 mm bore, this kit helps restore compression and oil sealing for reliable trail and farm performance. Built to meet or exceed stock specifications in a cost-effective aftermarket package, it provides a dependable rebuild path without OEM pricing tags.

This aftermarket replacement focuses on restoring ring seating and sealing surface integrity after years of wear, delivering consistent power and reduced oil consumption on rugged off-road use. With an oversize +0.50 mm configuration, it returns the engine to dependable operation, making it a smart choice for riders and workers who rely on their TRX300 for daily tasks and weekend adventures.

Comprehensive Vehicle Fitment

Data verified via OEM catalogs and aftermarket cross-reference references for TRX300/TRX300FW compatibility.

Product Specifications

OEM & Aftermarket Cross-Reference Information

What's Included

This kit includes the following components for one piston, ready to install on the TRX300 engine:

• Top Ring
• Second Ring
• Oil Ring (x2)
• Oil Ring Spacer

Note: This kit contains piston rings only. Piston, pins, circlips, gaskets, and other related components are not included unless specified elsewhere.

Why Choose This Aftermarket Replacement?

• Direct-Fit Compatibility: Precisely matched to TRX300 FourTrax (1988-2000) and TRX300FW 4x4, ensuring seamless installation.
• OEM Cross-Reference: Backed by established OEM references (13031-HC4-306) with reliable aftermarket alternatives for cost efficiency.
• Accurate Oversize Restoration: +0.50 mm oversize to restore ring seating, compression, and oil sealing on worn bores.
• OE-Style Materials & Geometry: Cast Iron rings designed to mimic original cross-section and seating behavior for reliable heat expansion and wear characteristics.
• Complete Ring Set: Includes top, second, oil rings, and spacer for one piston, simplifying rebuilds and reducing missing parts.
• Cost-Effective Performance: Delivers OEM-grade performance at a fraction of the price, helping you get back on the trail or job faster.

Installation Notes:

• Prepare the top end: drain oil, remove the cylinder head, and inspect the bore for scoring or glazing before installing a +0.50 mm oversize kit.
• Use a proper ring-expansion tool to avoid ring damage; install rings in the correct order (top ring, second ring, then oil rings with spacers).
• Inspect ring grooves and piston lands; clean all surfaces and lightly oil rings before installation to prevent galling.
• Orient ring gaps per service manual recommendations and keep gaps staggered to minimize blow-by; ensure correct ring orientation on the piston.
• Reassemble with new gaskets as needed, then torque head bolts per the factory pattern and perform a careful break-in procedure as recommended in the service manual.
• After running-in, perform a leak-down and compression test to verify a proper seal and ring seating before returning to service.

Why Upgrade?

Running a worn piston ring set on a TRX300 engine can lead to persistent blow-by, reduced compression, and oil consumption that erodes performance under load. This aftermarket replacement restores proper bore clearance and sealing, reestablishing reliable power and oil control for continued trail, work, and play.