OS 1.00 OEM Direct Fit Piston Kit for Yamaha YFM 660 Grizzly, Rhino, and Raptor models from 2002 through 2007 is a purpose-built engine component designed to restore factory compression and dependable power. This aftermarket replacement delivers a cost-effective path to peak performance without sacrificing the tolerances required for long-term reliability. Built to align with Yamaha specifications, it provides a direct-fit solution that helps your trail or farm work run smoother, cooler, and more reliably crank after crank.

The OS 1.00 piston kit offers a clear value proposition for riders facing typical wear on these engines—declining compression, oil consumption, and throttle response slowdowns from worn piston rings and lands. By delivering a properly sized, durable aluminum piston with precise ring fit, this aftermarket option helps restore consistent power and reliable sealing in dusty, heavy-use conditions common on trails and in fields, all while keeping operating costs down.

Comprehensive Vehicle Fitment

Product Specifications

OEM & Aftermarket Cross-Reference Information

What's Included

Includes the essential top-end components needed to rebuild the piston area on Yamaha YFM 660 engines:

• Piston
• Piston Rings
• Wrist Pin
• Circlips

*Gaskets and top-end seals are not included; use a separate top-end gasket kit for a complete rebuild.*

Why Choose This Aftermarket Replacement?

• Direct-Fit Compatibility: Engineered to bolt into Yamaha YFM 660 Grizzly, Rhino, and Raptor models within the 2002–2007 window with minimal prep work.
• OEM Cross-Reference: Aligns with Yamaha OEM references 2C6-11638-00-00 and 3YF-11638-00-00 for easy sourcing and matching parts.
• Premium Materials: Aluminum alloy piston designed for strength, heat tolerance, and reliable ring seal under typical off-road conditions.
• Engine Reliability Restoration: Restores compression and sealing, helping restore power delivery and reduce oil consumption in demanding trail or farm use.
• Cost-Effective Replacement: A budget-conscious option that preserves original performance without the premium OEM price tag.
• Performance Restoration: Reinstates factory-like throttle response and torque, enabling confident starts, climbs, and load handling.

Installation Notes:

• Inspect the cylinder bore for scoring or out-of-round wear; hone or bore as necessary before installing the kit.
• Verify the bore diameter and OS size match the kit’s specifications; ensure no debris or burrs remain in the cylinder.
• Lubricate the piston, rings, and wrist pin with assembly lubricant prior to assembly to prevent dry-start wear.
• Install the wrist pin and circlips securely; confirm circlips are fully seated and not protruding into the crankcase.
• Orient piston rings correctly and stagger ring gaps to optimize sealing; verify ring end gaps per manual guidelines.
• Follow the engine service manual for proper torque specs and break-in procedures to avoid glazing or ring set failure.

Why Upgrade?

Running a worn piston dimension or degraded ring seal on the YFM 660 series leads to compression loss, reduced power, higher oil consumption, and potential overheating. Upgrading to this OS 1.00 piston kit restores proper compression and sealing, delivering dependable power and reliability for demanding trail work or farm duties.