Restore peak compression and a reliable seal in your 250cc quad’s top end with the OS 1.00 piston ring kit. This oversized ring set is designed for engines with a 71.0 mm bore, covering model years from 1989 through 2009 to refresh power, throttle response, and oil-control on trail or farm work. The OS 1.00 specification targets bore wear, delivering consistent end gaps and strong ring tension for a dependable rebuild without paying OEM prices. Built for durability under heat and friction, this kit helps reclaim torque and smooth revs across the entire RPM range.

With a focus on real-world riding wear, this aftermarket replacement targets common wear problems like blow-by and oil consumption that creep in as the bore widens. Its precisely matched OS 1.00 rings deliver reliable sealing, improved ring-pack stability under load, and long-lasting performance for tough conditions, whether logging a long trail ride or pulling heavy loads on the farm. It brings a factory-like rebuild experience at a value-focused price point, making it a trusted choice for older builds where availability and parts pricing matter.

Comprehensive Vehicle Fitment

Source notes: model coverage aligns with Yamaha 250cc quad lineups spanning late 1980s through the late 2000s, including Timberwolf, Bear Tracker, and related variants.

Product Specifications

Notes: OEM reference and OS sizing reflect common Yamaha service data for 71.0 mm bores and OS 1.00 ring sets used across the late 1980s to 2000s 250cc quad lineup.

OEM & Aftermarket Cross-Reference Information

Notes: cross-reference references reflect typical interchangeability used in aftermarket catalogs for Yamaha 250cc quad rings sets; confirm local supplier listings for exact cross-reference naming.

What's Included

A compact, ready-to-install kit designed for a straightforward piston-ring upgrade. Includes:

• Top Compression Ring
• Second Compression Ring
• Oil Ring

Note: Piston pin and circlips are not included with this ring kit. Separate components such as the pin (e.g., 29U-11633-00) and circlips may be required for complete assembly.

Why Choose This Aftermarket Replacement?

• Direct-Fit Compatibility: Precisely sized OS 1.00 rings designed to seal Yamaha YFM/YFB 250 cylinders without modification.
• OEM Cross-Reference: Backed by cross-reference with Yamaha part numbers to ensure reliable interchangeability across markets.
• Premium Materials: Robust steel alloy construction with OEM-style finishes to resist heat and wear in high-load applications.
• Performance Restoration: Restores compression and ring-end stability, improving throttle response and torque across the rev range.
• Cost-Effective Value: A practical rebuild option that delivers OEM-like performance without OEM pricing.
• Availability for Older Builds: Specifically suited for mid-to-late 1990s–2000s models where OEM stock may be scarce.

Installation Notes:

• Check bore wear before install: verify the 71.0 mm standard bore and confirm OS 1.00 sizing necessity for your cylinder.
• Ring orientation matters: install the top and second compression rings with bevel facing up; ensure the oil ring spacer is seated correctly.
• Pre-lubricate: apply assembly lube to all rings and mating surfaces to minimize installation scuffing.
• Clean grooves and decks: thoroughly clean ring grooves and the piston crown to prevent binding or micro-gaps.
• Double-check end gaps: confirm gaps meet OEM-style tolerances to avoid ring sticking or blow-by on startup.
• Use correct torque and assembly steps: follow shop manual guidelines for piston ring end-gap orientation and ring seating after initial startup.

Why Upgrade?

Running a worn piston-ring set leads to blow-by, reduced compression, and increased oil consumption, especially under heavy throttle and load. Replacing with an OS 1.00 kit restores seal integrity, reclaiming power and reliability for long trail sessions or field chores.