{"product_id":"wossner-8321d400-piston-kit-2022-2026-yamaha-yz125-yz125x-4-00mm-oversize","title":"Wossner 8321D400 Piston Kit - 2022-2026 Yamaha YZ125 YZ125X +4.00mm Oversize","description":"\u003ch3\u003eWossner 8321D400 Standard Series Forged 2-Stroke Piston Kit - +4.00mm Oversize\u003c\/h3\u003e\n\n\u003cp\u003ePush the limits of your small-bore engine with the Wossner 8321D400 Piston Kit. Specifically designed for the latest generation 2022-2026 Yamaha YZ125 and YZ125X models, this +4.00mm oversize forged kit is the ultimate choice for custom big-bore builds or for salvaging cylinders that require extensive boring and replating to 58.00mm. At Moto-House MX, we know that serious racers and builders trust Wossner’s aerospace-grade forgings to provide the structural integrity required when increasing displacement and power.\u003c\/p\u003e\n\n\u003cp\u003eForged from premium aluminum alloy, the 8321D400 features a performance-driven single-ring design to minimize internal friction and maximize peak RPM. Despite the significant jump in diameter to 58.00mm, Wossner utilizes advanced machining to keep the piston lightweight, ensuring your YZ retains the rapid throttle response and \"flickability\" that defines the 125cc class. The permanent skirt coating is vital in these larger-bore applications, reducing internal drag and piston rock for a quieter running engine and a reliable break-in. This 57.95mm piston is precision-matched for 58.00mm bores, offering a durable, high-performance solution for your custom Yamaha build.\u003c\/p\u003e\n\n\u003ch3\u003eTop Features: Wossner 8321D400 Piston Kit\u003c\/h3\u003e\n\u003cul\u003e\n    \u003cli\u003e\n\u003cb\u003e+4.00mm Oversize (57.95mm):\u003c\/b\u003e Engineered specifically for 58.00mm bores, allowing for increased displacement and the repair of heavily damaged cylinders.\u003c\/li\u003e\n    \u003cli\u003e\n\u003cb\u003eSingle Ring Design:\u003c\/b\u003e Minimizes friction and drag, allowing for the extreme RPMs and high-end power required for competitive motocross.\u003c\/li\u003e\n    \u003cli\u003e\n\u003cb\u003eAerospace-Grade Forging:\u003c\/b\u003e Significantly stronger than stock cast pistons, offering superior fatigue resistance for high-stress racing conditions.\u003c\/li\u003e\n    \u003cli\u003e\n\u003cb\u003eLow-Friction Skirt Coating:\u003c\/b\u003e Permanent molybdenum disulphide coating protects the cylinder wall and ensures smooth operation under high thermal loads.\u003c\/li\u003e\n    \u003cli\u003e\n\u003cb\u003eOptimized Lightness:\u003c\/b\u003e Machined to remove excess mass while reinforcing the crown and skirt for professional-grade durability.\u003c\/li\u003e\n    \u003cli\u003e\n\u003cb\u003eComplete Assembly:\u003c\/b\u003e Kit includes the forged piston, high-performance ring, wrist pin, and circlips.\u003c\/li\u003e\n\u003c\/ul\u003e\n\n\u003cp\u003e\u003cb\u003eExpert Pro-Tip:\u003c\/b\u003e Moving to a +4.00mm oversize is a major modification that requires the cylinder to be professionally bored and replated to a 58.00mm finished size. This effectively turns your engine into a \"big bore\" 125, often requiring changes to your jetting and power valve clearance. When installing the 8321D400, always double-check your ring end gap and ensure the cylinder head is modified to accommodate the larger 58mm bore. Pairing this build with a fresh top-end gasket kit and high-quality 2-stroke premix oil will ensure your big-bore Yamaha performs at its peak.\u003c\/p\u003e\n\n\u003ch3\u003eFitment List\u003c\/h3\u003e\n\u003ctable border=\"1\" cellpadding=\"8\" style=\"width: 100%; border-collapse: collapse;\"\u003e\n    \u003cthead\u003e\n        \u003ctr\u003e\n            \u003cth\u003eYear Range\u003c\/th\u003e\n            \u003cth\u003eVehicle Brand\u003c\/th\u003e\n            \u003cth\u003eVehicle Model\u003c\/th\u003e\n        \u003c\/tr\u003e\n    \u003c\/thead\u003e\n    \u003ctbody\u003e\n        \u003ctr\u003e\n            \u003ctd\u003e2022-2026\u003c\/td\u003e\n            \u003ctd\u003eYamaha\u003c\/td\u003e\n            \u003ctd\u003eYZ125 (Standard, Monster Energy, 50th\/70th Anniversary)\u003c\/td\u003e\n        \u003c\/tr\u003e\n        \u003ctr\u003e\n            \u003ctd\u003e2023-2026\u003c\/td\u003e\n            \u003ctd\u003eYamaha\u003c\/td\u003e\n            \u003ctd\u003eYZ125X (Cross Country)\u003c\/td\u003e\n        \u003c\/tr\u003e\n    \u003c\/tbody\u003e\n\u003c\/table\u003e\n\n\u003ch3\u003eFrequently Asked Questions\u003c\/h3\u003e\n\u003cp\u003e\u003cb\u003eQ: Is this a drop-in piston for a stock bike?\u003c\/b\u003e\u003cbr\u003e\nA: No, this is a +4.00mm oversize piston. Your cylinder must be bored and replated to exactly 58.00mm to use this piston kit.\u003c\/p\u003e\n\n\u003cp\u003e\u003cb\u003eQ: Will this increase my engine's displacement?\u003c\/b\u003e\u003cbr\u003e\nA: Yes, boring your cylinder to 58.00mm will increase the displacement beyond the stock 125cc, providing more torque and potential power, though it may change your racing class eligibility.\u003c\/p\u003e\n\n\u003cp\u003e\u003cb\u003eQ: Does this kit include the gasket set?\u003c\/b\u003e\u003cbr\u003e\nA: No, the kit includes the forged piston, ring, wrist pin, and clips. A complete top-end gasket set is sold separately and is required for a professional rebuild.\u003c\/p\u003e\n\n\u003ch3\u003eRecommended Pairings\u003c\/h3\u003e\n\u003cul\u003e\n    \u003cli\u003e\n\u003cb\u003eComplete Top End Gasket Set:\u003c\/b\u003e Ensure a professional, leak-free seal for your custom engine build.\u003c\/li\u003e\n    \u003cli\u003e\n\u003cb\u003eYamalube 2-R Premix Oil:\u003c\/b\u003e The gold standard for keeping high-performance Yamaha 2-strokes running clean and protected.\u003c\/li\u003e\n\u003c\/ul\u003e\n\n\u003cp\u003eRestore your machine’s power and precision today. Buy now at Moto-House MX!\u003c\/p\u003e\n\n\u003cp\u003e\u003cb\u003eMoto-House MX – Choice of Champions\u003c\/b\u003e – is located in Clermont\/Montverde, FL. The Best Motocross\/UTV \u0026amp; ATV Shop in Central Florida. Stop by our local store in Montverde, FL or enjoy lightning-fast shipping across the USA.\u003c\/p\u003e\n\n\u003cscript type=\"application\/ld+json\"\u003e\n{\n  \"@context\": \"https:\/\/schema.org\/\",\n  \"@type\": \"Product\",\n  \"name\": \"Wossner 8321D400 Piston Kit\",\n  \"image\": [],\n  \"description\": \"Premium Wossner 8321D400 Forged 2-Stroke Single Ring Piston Kit for 2022-2026 Yamaha YZ125 and YZ125X. +4.00mm Oversize (57.95mm) for 58.00mm bore.\",\n  \"sku\": \"8321D400\",\n  \"brand\": {\n    \"@type\": \"Brand\",\n    \"name\": \"Wossner\"\n  },\n  \"offers\": {\n    \"@type\": \"Offer\",\n    \"url\": \"https:\/\/motohousemx.com\/products\/wossner-8321d400-piston-kit\",\n    \"priceCurrency\": \"USD\",\n    \"availability\": \"https:\/\/schema.org\/InStock\"\n  }\n}\n\u003c\/script\u003e","brand":"WOSSNER","offers":[{"title":"Default Title","offer_id":44495998582867,"sku":"8321D400","price":152.0,"currency_code":"USD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/1754\/5421\/files\/2756511.png?v=1776229962","url":"https:\/\/motohousemx.com\/products\/wossner-8321d400-piston-kit-2022-2026-yamaha-yz125-yz125x-4-00mm-oversize","provider":"Moto-House MX","version":"1.0","type":"link"}