Wossner 8134D150 Piston Kit - Yamaha YZ250 WR250 1988-1991 +1.50mm Oversize

Wossner 8134D150 Standard Series Forged 2-Stroke Piston Kit - +1.50mm Oversize

Give your vintage Yamaha YZ or WR a second chance with the Wossner 8134D150 Piston Kit. Specifically designed for the 1988-1991 Yamaha YZ250 and the 1991 WR250, this +1.50mm oversize forged kit is the professional solution for cylinders that require significant boring to remove deep scoring or wear. At Moto-House MX, we specialize in keeping legendary 2-strokes on the track; Wossner’s aerospace-grade forging provides a massive durability upgrade over traditional cast pistons, ensuring your 250cc engine can handle the heat and pressure of modern riding.

The 8134D150 features a dual-ring configuration, which is ideal for the broad powerbands of late 80s and early 90s Yamahas. This design provides superior heat dissipation and a long-lasting compression seal, helping your engine maintain consistent power throughout the moto. To ensure smooth operation and reduced engine noise, Wossner applies a permanent molybdenum disulphide skirt coating that minimizes friction and protects the cylinder wall. Precision-machined for a 69.50mm finished bore, this 69.44mm piston kit restores your Yamaha to peak mechanical performance.

Top Features: Wossner 8134D150 Piston Kit

• +1.50mm Oversize (69.44mm): The perfect choice for cylinders that need to be bored out to remove deep scratches, resulting in a fresh 69.50mm bore size.
• Dual Ring Configuration: Offers enhanced cooling and a reliable compression seal, maintaining power in both motocross and off-road environments.
• Aerospace-Grade Forging: Engineered to be significantly stronger and more heat-resistant than original cast equipment.
• Low-Friction Skirt Coating: Permanent skirt treatment reduces internal drag and protects the cylinder wall for a quieter engine and smoother break-in.
• Optimized Machining: Precisely balanced to reduce reciprocating weight while maintaining maximum strength in the crown and skirt walls.
• Complete Kit: Includes the high-performance forged oversize piston, rings, wrist pin, and circlips.

Expert Pro-Tip: When moving to a +1.50mm oversize, it is critical that your cylinder is precision-bored and honed by a qualified machine shop to exactly 69.50mm. This ensures the correct piston-to-wall clearance for a forged assembly. For a professional-grade rebuild, always install with a fresh top-end gasket kit and use high-quality 2-stroke premix oil to protect your new forged piston during the initial heat cycles.

Fitment List

Year Range	Vehicle Brand	Vehicle Model
1988-1991	Yamaha	YZ250
1991	Yamaha	WR250

Frequently Asked Questions

Q: Why use an oversize piston instead of a new cylinder?
A: Boring your existing cylinder to a +1.50mm oversize is a cost-effective way to restore factory performance. It removes damage while allowing you to keep the original cylinder casting, which is often higher quality than aftermarket replacements.

Q: Is a forged piston better for my 1990 YZ250?
A: Yes. Forged pistons are much more resilient to the heat and stress of high-performance 2-strokes. They offer a higher level of structural integrity, which is essential for engines that are 30+ years old.

Q: Does this kit include the wrist pin bearing?
A: This kit includes the forged piston, dual rings, wrist pin, and circlips. The small-end needle bearing is sold separately. We always recommend installing a new bearing with every top-end rebuild.

Recommended Pairings

• Complete Top End Gasket Set: Vital for a leak-free seal and proper engine cooling.
• Premium 2-Stroke Premix Oil: Ensure your new oversize forged piston is protected from the very first start.

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.