Wossner 8330DB Piston Kit - 2002-2026 Yamaha YZ85 Standard Size B

Wossner 8330DB Standard Series Forged 2-Stroke Piston Kit - Standard Size B

Maintain the competitive edge of your mini-racer with the Wossner 8330DB Piston Kit. Tailored specifically for the 2002-2026 Yamaha YZ85, the "Size B" piston is the professional's choice for engines that have seen some track time. At Moto-House MX, we understand that as a cylinder wears, factory "Size A" clearances can become too loose; this +0.01mm Size B kit provides the precise fitment needed to restore compression and eliminate piston slap in slightly worn bores.

Forged from high-grade aerospace aluminum alloy, the 8330DB is built to withstand the punishing RPMs of 85cc motocross competition. The dual-ring design is a key feature for the YZ85, offering improved secondary compression and superior heat transfer to the cylinder wall, which helps maintain power throughout long, hot motos. To ensure longevity, Wossner applies a permanent molybdenum disulphide skirt coating that reduces friction and protects the cylinder during high-stress operation. With optimized machining for a perfect strength-to-weight ratio, this 47.46mm piston ensures your YZ85 retains its legendary throttle response while gaining the durability of a forged component.

Top Features: Wossner 8330DB Piston Kit

• Standard Size B (47.46mm): Specifically designed for 47.51mm bores, providing a tighter fit for cylinders with slight wear to restore peak performance.
• Dual Ring Configuration: Enhances cylinder sealing and cooling, ensuring consistent power delivery for demanding mini-moto racers.
• Aerospace-Grade Forging: Offers superior structural integrity compared to stock cast pistons, significantly reducing the risk of skirt failure at high RPM.
• Low-Friction Skirt Coating: Permanent coating reduces internal drag and piston rock for a quieter running engine and longer service life.
• Precision Lightness: Engineered to minimize reciprocating mass, allowing the engine to rev freely and respond instantly to rider input.
• Complete Top-End Kit: Includes the forged Size B piston, performance rings, wrist pin, and circlips.

Expert Pro-Tip: When your YZ85 has 20-30 hours of hard riding, the cylinder bore often grows by a fraction of a millimeter. Stepping up to a Wossner Size B (47.46mm) is the standard practice for top-tier mechanics to bring the piston-to-wall clearance back to ideal specifications without needing a full replate. Always measure your cylinder with a bore gauge to confirm that 47.51mm is your current size. For the best results, install with a fresh top-end gasket kit and use premium 2-stroke oil to protect your investment.

Fitment List

Year Range	Vehicle Brand	Vehicle Model
2002-2026	Yamaha	YZ85 / YZ85LW (Large Wheel)

Frequently Asked Questions

Q: When should I use a Size B piston instead of Size A?
A: Size B (47.46mm) is used when your cylinder has minor wear. If your standard 47.50mm bore has increased slightly toward 47.51mm, the Size B provides the correct clearance to prevent power loss and excessive piston movement.

Q: Does a forged piston require a different break-in than a cast one?
A: Yes, forged pistons expand differently under heat. We recommend a couple of heat cycles followed by a progressive riding session to ensure the rings seat perfectly and the piston stabilizes within the bore.

Q: Is this kit compatible with the YZ85 Large Wheel?
A: Yes, the engine specifications for the YZ85 and YZ85LW are identical, and this kit fits both models perfectly.

Recommended Pairings

• Complete Top End Gasket Set: Essential for maintaining proper squish clearance and a leak-free seal.
• Yamalube 2-R Premix Oil: Specifically formulated to protect high-performance Yamaha racing engines.

Restore your machine’s power and precision today. Buy now at Moto-House MX!

Moto-House MX – Choice of Champions – is located in Clermont/Montverde, FL. The Best Motocross/UTV & ATV Shop in Central Florida. Stop by our local store in Montverde, FL or enjoy lightning-fast shipping across the USA.