A precise OS 1.00 oversize piston ring kit designed for single-cylinder 350/400cc ATV engines from 1987 through 2011, this kit restores compression by sealing a bore worn from years of hard off-road use. It targets the exact ring set sizing needed to reestablish peak power and efficient combustion in older, high-demand quads, without the need to source OEM parts. This aftermarket replacement provides a cost-effective, reliable rebuild option for trail riding or farm work where every horsepower matters.

Built to withstand dusty, hot, and vibrating environments, this OS 1.00 kit reclaims lost compression and reduces oil consumption by renewing the piston-to-bore seal. Its oversize design compensates for bore wear, delivering consistent ring tension and durable performance when you’re rebuilding a single-cylinder powerplant in your utility ATV. For riders and farmers who depend on dependable engine restoration, this kit offers a trustworthy balance of fit, function, and value.

Comprehensive Vehicle Fitment

Fitment data is based on OEM and aftermarket listings for the YFM 350/400 series engines spanning 1987-2011.

Product Specifications

OEM & Aftermarket Cross-Reference Information

What's Included

All the essential rings needed to restore sealing on a single YFM 350/400 cylinder with OS 1.00 sizing:

• Top compression ring (OS 1.00)
• Second compression ring (OS 1.00)
• Oil control ring set (OS 1.00)

Note: Piston, wrist pin, circlips, and gaskets are not included in this kit.

Why Choose This Aftermarket Replacement?

• Direct-Fit Compatibility: Precisely sized OS 1.00 for YFM 350/400 engines to restore original compression and power.
• OEM Cross-Reference: Cross-referenced to Yamaha part 4GB-11610-40-00, ensuring reliable compatibility with OEM specifications.
• Premium Materials: Durable cast iron with chromium facing on the top ring and chrome-coated secondary rings for wear resistance in dusty, high-heat environments.
• Oversize Precision: +1.00 mm oversize to correct bore wear and re-seal the combustion chamber effectively.
• Reliability in Hard-Duty Use: Built to withstand trail abuse and farm grit, delivering consistent sealing and longer service life.
• Cost-Effective Rebuild: A practical solution to restore performance without the expense of OEM-only sourcing.

Installation Notes:

• Inspect the bore: Before installation, measure bore wear and confirm OS size suitability for the rebuild.
• Cleanliness matters: Thoroughly clean the cylinder and oil passages; remove all grit and carbon before ring installation.
• Rings handling: Use a proper ring expander or appropriate tool to avoid nicking the rings; keep rings flat and unbent.
• Lubrication: Lightly lubricate all rings with clean engine oil to ease installation and seating.
• Ring orientation: Install the top ring with the correct face orientation and stagger end gaps away from each other to prevent blow-by.
• Ring seating & inspection: After assembly, perform a compression test and inspect for blow-by or uneven seating during initial startup.

Why Upgrade?

Running a worn piston ring set can dramatically reduce compression, increase oil consumption, and steal power. Upgrading to this OS 1.00 oversized kit restores sealing, improves compression, and returns the engine’s performance and reliability for trail and farm duty alike. It’s a practical rebuild choice when bore wear has begun impacting daily operation.