Wossner 8942DB Piston Kit - 2016-2019 Yamaha YZ250F YZ250FX WR250F Standard Size B

Wossner 8942DB Pro Series Forged 4-Stroke Piston Kit - Standard Size B

Keep your Yamaha’s reverse-cylinder engine screaming at the front of the pack with the Wossner 8942DB Piston Kit. Specifically engineered for the 2016-2018 YZ250F and 2017-2019 YZ250FX / WR250F models, this "Size B" Pro Series forged kit is the professional’s choice for engines that have logged several race weekends. At Moto-House MX, we know that Yamaha’s high-revving 250 platform demands strict tolerances; this +0.01mm Size B kit provides the precise fitment needed to restore compression and ensure your bike retains its legendary mid-to-top end pull.

Forged from high-performance aluminum alloy, the 8942DB features a performance-oriented 13.7:1 compression ratio, designed to sharpen throttle response and optimize combustion efficiency. This Pro Series kit incorporates Wossner’s advanced radial boss machining and enhanced oiling slots, which significantly improve wrist pin lubrication under the extreme heat of motocross and cross-country racing. The permanent molybdenum disulphide skirt coating reduces internal friction and protects the cylinder during high-RPM operation. This Size B piston (76.96mm) is precision-matched for 77.01mm bores, offering a factory-spec fit for cylinders with minor wear.

Top Features: Wossner 8942DB Piston Kit

• Standard Size B (76.96mm): Precision-machined for 77.01mm bores to compensate for minor cylinder expansion and restore ideal engine tolerances.
• 13.7:1 High Compression: Engineered to maximize power output and engine efficiency, providing a noticeable performance boost over standard stock configurations.
• Pro Series Forged Design: Offers elite-level strength and a lightweight profile, allowing for faster revving and superior durability under racing conditions.
• Advanced Lubrication System: Features enhanced oiling slots and annular grooves to ensure the wrist pin remains lubricated during intense competition.
• Low-Friction Skirt Coating: Permanent skirt treatment minimizes drag, protects the cylinder wall, and ensures a smoother break-in period.
• Comprehensive Racing Kit: Includes the high-compression forged piston, performance rings, wrist pin, and pin locks.

Expert Pro-Tip: Yamaha YZ250F engines are known for their durability, but the high-revving nature of the reverse-head design means top-end maintenance is critical. If your cylinder has 30+ hours of ride time, stepping up to a Wossner Size B (76.96mm) is the expert way to bring your piston-to-wall clearance back to perfection without a full re-plating service. Always confirm your bore measurement is 77.01mm before installation. For maximum longevity, install with a fresh top-end gasket kit and use premium synthetic oil to protect your new forged assembly.

Fitment List

Year Range	Vehicle Brand	Vehicle Model
2016-2018	Yamaha	YZ250F
2017-2019	Yamaha	YZ250FX
2018-2019	Yamaha	WR250F

Frequently Asked Questions

Q: When should I choose Size B over Size A?
A: Size B (76.96mm) is 0.01mm larger than Size A. It is the standard choice for your second or third top-end rebuild to account for the microscopic wear that occurs on the cylinder walls, ensuring you maintain a perfect seal for maximum power.

Q: Is this kit compatible with the cross-country FX and WR models?
A: Yes, this kit is specifically designed to fit the YZ250FX and WR250F models within the 2017-2019 year range, offering the same high-performance forged benefits as the motocross version.

Q: Does a 13.7:1 compression ratio require race fuel?
A: 13.7:1 is a performance-oriented ratio that typically runs well on high-quality 93 octane pump gas. However, many racers prefer a 50/50 race gas blend to ensure the highest level of protection against detonation in high-heat conditions.

Recommended Pairings

• Complete Top End Gasket Set: Vital for ensuring a perfect seal and maintaining the correct squish gap for high-compression performance.
• Motul 300V 4T Factory Line Oil: Provides the extreme pressure protection required for high-revving Yamaha 4-stroke 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.