Upgrade the heart of your Yamaha YFM 350/400 engine with this Oversize OS 0.75 Piston Ring Kit, engineered to restore compression and seal in rebuilt engines across a broad range of YFM models. It is designed for cylinders that have been overbored to the final OS 0.75 specification, delivering reliable performance when trail work, hunting, or farm duty demands more from the motor. This OS 0.75 piston ring kit is a practical aftermarket replacement that helps you reclaim throttle response and steady power without the cost of OEM parts.

Built for durability under demanding off-road use, this oversize piston ring kit targets the common wear points that plague overhauled 350/400 engines—loss of compression, reduced power, and sloppy low-end torque. The OS 0.75 specification ensures a precise ring gap and seal after overboring, maintaining reliable ring seal and consistent combustion. In rugged trail and farm scenarios, this replacement helps you regain the predictable power curve you remember from your machine's early days.

Comprehensive Vehicle Fitment

Product Specifications

OEM & Aftermarket Cross-Reference Information

*OEM cross-reference numbers are provided for reference purposes only. These numbers indicate the lineage of oversize rings; always verify your final bore size (83.75mm) before ordering.*

What's Included

This OS 0.75 oversize piston ring kit ships with the essential components to rebuild one Yamaha YFM cylinder.

• Top Ring (chrome-faced)

• Second Ring

• Oil Ring Set (including expander spacer)

Note: This is a piston ring kit only. It does not include the piston, wrist pin, circlips, or gaskets.

Why Choose This Aftermarket Replacement?

• Precise Oversize Fit: Specifically designed for engines with a final bore size of 83.75mm (OS 0.75), ensuring correct ring gap and optimal sealing after overboring.

• OEM Lineage Cross-Reference: Follows the oversize progression of OEM rings (0.25, 0.50, 0.75), making it the logical next step for a professionally rebuilt cylinder.

• Restores Compression: New rings restore proper ring tension and seal, directly addressing power loss, blow-by, and high oil consumption.

• Durable Construction: Features a chrome-faced top ring for superior heat resistance and wear longevity, built to withstand the demands of high-revving engines and tough terrain.

• Complete Ring Set: Includes all three rings (top, second, and oil ring set) required for a complete piston seal.

• Cost-Effective Rebuild: Delivers reliable performance at an aftermarket price, ideal for extending the life of your machine without a full OEM investment.

Installation Notes:

• Verify Bore Size: Confirm the engine cylinder has been professionally overbored to the final size of 83.75mm before ordering. This kit is not for standard or other oversize bores.

• Professional Machining Recommended: A proper overbore and hone by a qualified machine shop is essential for the new rings to seat correctly and achieve a long-lasting seal.

• Check Ring End Gap: Always check and adjust ring end gaps according to the service manual specifications after the bore is confirmed.

• Lubricate Before Installation: Lubricate the piston, rings, and cylinder wall with clean engine oil or assembly lube prior to installation.

• Orient Rings Correctly: Ensure rings are installed with the correct orientation and that the ring gaps are staggered according to the service manual to prevent blow-by.

• Follow Service Manual: Adhere to all torque specifications and break-in procedures outlined in the Yamaha service manual.

Why Upgrade?

Running a worn-out piston ring set in a bore that's already been worked over compromises compression, throttle response, and reliability. This OS 0.75 oversize ring kit restores proper compression and consistent power delivery, helping your YFM 350/400 run reliably through tough trails and demanding work. A fresh ring seal reduces piston slap and the risk of scoring, reducing the chance of a sudden loss of power on rugged terrain.

Order your piston ring kit today and get back on the trail with confidence.