Engine restoration that makes the TRX450 Foreman feel new again starts with a Precision Piston Ring Kit OS 0.25. This aftermarket replacement is designed for Honda TRX450 Foreman models from 1998 through 2004 and uses a TEIKOKU ring material to closely match OE performance. Sized for a standard 90 mm bore upgraded to 90.25 mm, it reestablishes compression, improves sealing, and keeps the engine breathing clean in dusty trail rides or hard farm work.

These OS 0.25 rings tackle common wear issues that plague high-mileage TRX450 Foreman engines: worn grooves, seal leaks, and end-gap drift that allow oil blow-by and compression loss. By restoring ring tension and sealing, this kit helps recover top-end power and reliability without the cost of OEM-only parts, making it a practical choice for trail machines and workhorse farms alike.

Comprehensive Vehicle Fitment

Product Specifications

OEM & Aftermarket Cross-Reference Information

What's Included

This kit includes the essential piston rings that restore compression and sealing for the TRX450 Foreman.

• Top compression ring
• Second compression ring
• Oil control ring

Note: Related components such as a piston, piston pin, circlips, base gaskets, or cylinder head gaskets are not included with this ring set.

Why Choose This Aftermarket Replacement?

• Direct-Fit Compatibility: Precisely sized for 90 mm standard bore, upgraded to 90.25 mm, matching the TRX450 Foreman engine geometry.
• OEM Cross-Reference: TEIKOKU material used to mirror OE performance; recognized in multiple catalogs as the 0.25 OS option (13011-HN0-A01 / A02).
• Premium Materials (Piston Ring): TEIKOKU-grade ring material chosen for durability and reliable sealing in dusty, heavy-use environments.
• Performance Restoration: Restores compression and reduces oil blow-by after bore wear, improving power delivery and top-end response.
• Cost-Effective Reliability: A practical aftermarket path to TRX450 Foreman reliability without OEM-only constraints.
• Compatibility Assurance: Verified cross-references align with TRX450 Foreman variants (S/ES/FE/FM) across 1998–2004 models.

Installation Notes:

• Inspect bore and ring grooves: If bore wear exceeds service limits, consider reboring to the next oversize and use the matching OS rings.
• Clean grooves and bores thoroughly: Remove carbon and debris to prevent ring stiction and uneven sealing.
• Check ring orientation: Install rings with markings facing up and keep top vs. second rings separated to avoid mixing.
• End-gap staggering: Space ring end gaps approximately 120 degrees apart to promote even oil control and sealing.
• Lubricate during assembly: Apply a light coat of clean engine oil to rings and bore before installation to ease seating.
• Follow OEM service limits: When measuring end gaps and bores, use service limits from the TRX450 manual to ensure proper clearance after installation.

Why Upgrade?

Running a worn piston ring set in a TRX450 Foreman can allow oil to bypass the rings, leading to reduced compression, higher oil consumption, and degraded throttle response. This OS 0.25 kit reestablishes the seal and ring tension, delivering restored compression and reliable power for trail duty or fieldwork.