{"product_id":"prox-01-2321-b-01-2321-c-piston-kit-yamaha-yz250-suzuki-rm250-moto-house-mx","title":"ProX Piston Kit (66.36mm B Size) 01.2321.B - Yamaha YZ250 \/ YZ250X \/ Suzuki RM250 1999-2026","description":"\u003ch1\u003e\u003cstrong\u003eProX Piston Kit (66.36mm B \/ 66.37mm C) 01.2321.B \/ 01.2321.C - Yamaha YZ250 \/ YZ250X \/ Suzuki RM250 1999-2026\u003c\/strong\u003e\u003c\/h1\u003e\n\u003cdiv style=\"background-color: #fdecea; border: 1px solid #f5c2c0; border-left: 5px solid #d93025; border-radius: 6px; padding: 10px 14px; margin: 12px 0; box-sizing: border-box; width: 100%; max-width: 100%; word-wrap: break-word; overflow-wrap: break-word; font-size: 15px; line-height: 1.5;\"\u003e\n\u003cstrong style=\"color: #b3261e;\"\u003ePlease Note:\u003c\/strong\u003e \u003cspan style=\"color: #5f1a15;\"\u003eThis listing features 2 different piston kit size options (Size B - 66.36 mm \/ MPN: 01.2321.B and Size C - 66.37 mm \/ MPN: 01.2321.C). Please select your required size option before finalizing your purchase.\u003c\/span\u003e\n\u003c\/div\u003e\n\u003ch3\u003eProduct Description\u003c\/h3\u003e\n\u003cp\u003eRefresh your top end with the \u003cstrong\u003eProX Piston Kit\u003c\/strong\u003e (MPNs 01.2321.B and 01.2321.C), manufactured in Japan as a direct OEM-style replacement for high-performance 250cc 2-stroke engines. Available in two precision size options—Size B (66.36mm) and Size C (66.37mm)—these pistons allow you to dial in exact piston-to-cylinder clearance on standard 66.40mm bore cylinders with broken-in or wearing plating. Each kit includes a piston, high-performance ring set, wrist pin, and circlips required for a complete top-end overhaul.\u003c\/p\u003e\n\u003cp\u003eCast from a high-silicon-content aluminum alloy, ProX pistons meet or exceed original equipment specifications for thermal expansion and durability. CNC-machined to extremely close tolerances, each piston features a low-friction Moly coated skirt that reduces drag and protects the cylinder wall during cold starts and high-RPM operation. Whether you are servicing your practice bike or prepping for race day, ProX delivers OEM performance and long-lasting reliability.\u003c\/p\u003e\n\u003ch3\u003eTop Features: ProX Piston Kit\u003c\/h3\u003e\n\u003cul\u003e\n\u003cli\u003eManufactured in Japan and designed as a direct OEM replacement top-end rebuild kit.\u003c\/li\u003e\n\u003cli\u003eAvailable in Size B (66.36mm) and Size C (66.37mm) options to precisely match cylinder plating wear.\u003c\/li\u003e\n\u003cli\u003eCast from a high-silicon-content aluminum alloy to meet or exceed OEM thermal and strength specifications.\u003c\/li\u003e\n\u003cli\u003eCNC-machined to extremely close tolerances with a low-friction Moly coated skirt.\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003cp\u003ePlease review the detailed compatibility data below to ensure an exact fitment match for your motorcycle before finalizing your purchase.\u003c\/p\u003e\n\u003ch3\u003eFitment List\u003c\/h3\u003e\n\u003ctable border=\"1\" cellpadding=\"5\" style=\"border-collapse: collapse; width: 100%;\"\u003e\n\u003cthead\u003e\n\u003ctr style=\"background-color: #f2f2f2;\"\u003e\n\u003cth\u003eYear Range\u003c\/th\u003e\n\u003cth\u003eVehicle Brand\u003c\/th\u003e\n\u003cth\u003eVehicle Model \u0026amp; Sub-Model\u003c\/th\u003e\n\u003c\/tr\u003e\n\u003c\/thead\u003e\n\u003ctbody\u003e\n\u003ctr\u003e\n\u003ctd\u003e1999-2026\u003c\/td\u003e\n\u003ctd\u003eYamaha\u003c\/td\u003e\n\u003ctd\u003eYZ250\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003e2003-2008\u003c\/td\u003e\n\u003ctd\u003eSuzuki\u003c\/td\u003e\n\u003ctd\u003eRM250\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003e2016-2026\u003c\/td\u003e\n\u003ctd\u003eYamaha\u003c\/td\u003e\n\u003ctd\u003eYZ250X\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003c\/tbody\u003e\n\u003c\/table\u003e\n\u003ch3\u003eFrequently Asked Questions\u003c\/h3\u003e\n\u003cp\u003e\u003cb\u003eQ: What is the difference between the B and C piston size options?\u003c\/b\u003e\u003cbr\u003eA: ProX manufactures pistons in slight increment sizing (A, B, C) to match cylinder wear on plated cylinders. Size B measures 66.36mm and Size C measures 66.37mm to compensate for normal cylinder plating wear and restore ideal piston-to-wall clearance on a standard 66.40mm bore.\u003c\/p\u003e\n\u003cp\u003e\u003cb\u003eQ: Does each option include all necessary hardware for a top-end piston replacement?\u003c\/b\u003e\u003cbr\u003eA: Yes, each ProX kit includes the selected piston, piston rings, wrist pin, and circlips.\u003c\/p\u003e\n\u003cp\u003e\u003cb\u003eExpert Pro-Tip:\u003c\/b\u003e Always measure your cylinder with a dial bore gauge prior to selecting your piston size grade. When installing new piston rings on a 2-stroke, check ring end gap inside the cylinder bore and make sure the ring locating pins on the piston align cleanly with the ring gaps to prevent snagging on exhaust or intake ports during assembly.\u003c\/p\u003e\n\u003ch3\u003eRecommended Pairings:\u003c\/h3\u003e\n\u003cul\u003e\n\u003cli\u003e\u003ca href=\"https:\/\/motohousemx.com\/collections\/yamaha-yz250-and-yz250x-performance-parts-collection-at-moto-house-mx\"\u003eYamaha YZ250 \u0026amp; YZ250X Performance Parts\u003c\/a\u003e\u003c\/li\u003e\n\u003cli\u003e\u003ca href=\"https:\/\/motohousemx.com\/collections\/suzuki-rm250-performance-upgrades-engine-mods-and-accessories-moto-house-mx\"\u003eSuzuki RM250 Performance Parts\u003c\/a\u003e\u003c\/li\u003e\n\u003cli\u003e\u003ca href=\"https:\/\/motohousemx.com\/collections\/yamaha-2-stroke-dirt-bikes-performance-parts-accessories-moto-house-mx\"\u003eYamaha 2-Stroke Performance Parts\u003c\/a\u003e\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003cp\u003eAt Moto-House MX, we carry the best brands in motocross and off-road performance. Our team has over 40 years of experience helping riders get more out of their bikes. We pride ourselves on great customer service, and every item ships FAST - straight to your door.\u003c\/p\u003e\n\u003cp\u003e\u003ci\u003e\u003cstrong\u003eMoto-House MX - Choice of Champions\u003c\/strong\u003e - Your premier powersports source with great customer service and lightning-fast shipping straight to your door.\u003c\/i\u003e\u003c\/p\u003e\n\u003cp\u003e \u003c\/p\u003e","brand":"ProX","offers":[{"title":"66.36 mm","offer_id":42253831438419,"sku":"01.2321.B","price":132.95,"currency_code":"USD","in_stock":true},{"title":"66.37 mm","offer_id":42253831471187,"sku":"01.2321.C","price":132.95,"currency_code":"USD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/1754\/5421\/files\/prox-oem-replacement-cast-piston-kit-1999-2023-yamaha-yz250-yz250x-974949.png?v=1735460469","url":"https:\/\/motohousemx.com\/products\/prox-01-2321-b-01-2321-c-piston-kit-yamaha-yz250-suzuki-rm250-moto-house-mx","provider":"Moto-House MX","version":"1.0","type":"link"}