{"product_id":"piston-kit-yamaha-yfm-350-big-bear-raptor-bruin-grizzly-os-1-50","title":"OS 1.50 Piston Kit for Yamaha YFM 350 Big Bear, Raptor, Bruin, and Grizzly OEM Replacement","description":"\u003cdiv\u003eOS 1.50 Piston Kit for Yamaha YFM 350 Big Bear, Raptor, Bruin, and Grizzly is a purpose-built top-end rebuild that increases displacement with a +1.50 mm oversize bore. It’s designed to restore compression and deliver stronger mid-range torque and quicker throttle response on the trail or farm, while staying true to Yamaha’s original engineering intent when used with the proper supporting parts. This aftermarket replacement is structured to offer a straightforward, reliable rebuild experience without OEM pricing. The kit is compatible across the YFM 350 platform, making it a versatile upgrade for multiple model lines. The OS 1.50 kit combines robust forged aluminum performance with an exacting fit for the YFM 350 family, addressing wear on the piston, rings, and related top-end components. By restoring compression and displacement, it helps recover lost low- and mid-range power and improves throttle feel under load. When paired with proper rings, wrist pin, and circlips, this oversize kit provides dependable operation for rugged trail work or farm duty, delivering lasting performance through the life of the rebuilt engine.\n\u003ch3\u003e\u003cbr\u003e\u003c\/h3\u003e\n\u003ch3\u003eComprehensive Vehicle Fitment\u003c\/h3\u003e\n\u003cp\u003eThis OS 1.50 piston kit aligns with Yamaha YFM350 engines across Warrior, Big Bear, Bruin, Grizzly, and Raptor lineages, covering a broad range of 4-stroke, air-cooled configurations used in trail and utility models.\u003c\/p\u003e\n\u003ctable\u003e\n\u003cthead\u003e\n\u003ctr\u003e\n\u003cth\u003eManufacturer\u003c\/th\u003e\n\u003cth\u003eModels \/ Series\u003c\/th\u003e\n\u003cth\u003eYears \/ Details\u003c\/th\u003e\n\u003c\/tr\u003e\n\u003c\/thead\u003e\n\u003ctbody\u003e\n\u003ctr\u003e\n\u003ctd\u003eYamaha\u003c\/td\u003e\n\u003ctd\u003eYFM350 Warrior (YFM350X)\u003c\/td\u003e\n\u003ctd\u003e1987–2004\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eYamaha\u003c\/td\u003e\n\u003ctd\u003eYFM350 WT Big Bear\u003c\/td\u003e\n\u003ctd\u003e1989–1999\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eYamaha\u003c\/td\u003e\n\u003ctd\u003eYFM350 Bruin\u003c\/td\u003e\n\u003ctd\u003eVarious years (4-stroke, air-cooled)\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eYamaha\u003c\/td\u003e\n\u003ctd\u003eYFM350 Grizzly\u003c\/td\u003e\n\u003ctd\u003e2007–2014 (Grizzly 350 family; 4x4 Auto and variants)\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eYamaha\u003c\/td\u003e\n\u003ctd\u003eYFM350 Raptor\u003c\/td\u003e\n\u003ctd\u003e2005–2013\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eYamaha\u003c\/td\u003e\n\u003ctd\u003eYFM350 Grizzly IRS 4x4 Auto\u003c\/td\u003e\n\u003ctd\u003e2007–2011\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003c\/tbody\u003e\n\u003c\/table\u003e\n\u003cp\u003eNote: fitment reflects how the YFM350 platform has been used across these model lines and years; always verify bore compatibility and supporting components during installation.\u003c\/p\u003e\n\u003ch3\u003eProduct Specifications\u003c\/h3\u003e\n\u003ctable\u003e\n\u003cthead\u003e\n\u003ctr\u003e\n\u003cth\u003eAttribute\u003c\/th\u003e\n\u003cth\u003eDetails\u003c\/th\u003e\n\u003c\/tr\u003e\n\u003c\/thead\u003e\n\u003ctbody\u003e\n\u003ctr\u003e\n\u003ctd\u003eOEM Reference Part Numbers\u003c\/td\u003e\n\u003ctd\u003e17211-HP0-A00, 17254-HN1-000, 17254-HP0-A00\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eType\u003c\/td\u003e\n\u003ctd\u003ePiston Kit\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eManufacturer\u003c\/td\u003e\n\u003ctd\u003eAftermarket Replacement\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eApplication\u003c\/td\u003e\n\u003ctd\u003eYamaha YFM 350 Big Bear, Raptor, Bruin, Grizzly 4-stroke engines\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eMaterial\u003c\/td\u003e\n\u003ctd\u003eForged aluminum\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eBore Oversize\u003c\/td\u003e\n\u003ctd\u003e+1.50 mm (approx. +0.059 in)\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eEngine Type\u003c\/td\u003e\n\u003ctd\u003e4-stroke\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003ePiston Style\u003c\/td\u003e\n\u003ctd\u003eOS oversize (piston kit)\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003c\/tbody\u003e\n\u003c\/table\u003e\n\u003ch3\u003e\u003cbr\u003e\u003c\/h3\u003e\n\u003ch3\u003eOEM \u0026amp; Aftermarket Cross-Reference Information\u003c\/h3\u003e\n\u003ctable style=\"width: 100%;\"\u003e\n\u003cthead\u003e\n\u003ctr\u003e\n\u003cth style=\"width: 19.4946%;\"\u003ePart Number\u003c\/th\u003e\n\u003cth style=\"width: 18.5688%;\"\u003eBrand \/ Type\u003c\/th\u003e\n\u003cth style=\"width: 61.2145%;\"\u003eCross-Reference Notes\u003c\/th\u003e\n\u003c\/tr\u003e\n\u003c\/thead\u003e\n\u003ctbody\u003e\n\u003ctr\u003e\n\u003ctd style=\"width: 19.4946%;\"\u003e17211-HP0-A00\u003c\/td\u003e\n\u003ctd style=\"width: 18.5688%;\"\u003eOEM Yamaha\u003c\/td\u003e\n\u003ctd style=\"width: 61.2145%;\"\u003eOriginal equipment reference; used for cross-checking OS oversize replacements and ensuring compatibility with rings\/wrist pin\/circlips\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd style=\"width: 19.4946%;\"\u003e17254-HN1-000\u003c\/td\u003e\n\u003ctd style=\"width: 18.5688%;\"\u003eOEM Yamaha\u003c\/td\u003e\n\u003ctd style=\"width: 61.2145%;\"\u003eOEM reference; serves as a cross-check point for aftermarket oversize kits\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd style=\"width: 19.4946%;\"\u003e17254-HP0-A00\u003c\/td\u003e\n\u003ctd style=\"width: 18.5688%;\"\u003eOEM Yamaha\u003c\/td\u003e\n\u003ctd style=\"width: 61.2145%;\"\u003eAlternative OEM reference; verify bore compatibility with the +1.50 mm oversize kit\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003c\/tbody\u003e\n\u003c\/table\u003e\n\u003ch3\u003e\u003cbr\u003e\u003c\/h3\u003e\n\u003ch3\u003eWhat's Included\u003c\/h3\u003e\n\u003cp\u003eA complete OS 1.50 piston kit ships with the core components needed for a top-end rebuild.\u003c\/p\u003e\n\u003cul\u003e\n\u003cli\u003e\n\u003cb\u003ePiston\u003c\/b\u003e assembly\u003c\/li\u003e\n\u003cli\u003e\n\u003cb\u003eRings\u003c\/b\u003e set\u003c\/li\u003e\n\u003cli\u003e\u003cb\u003eWrist Pin\u003c\/b\u003e\u003c\/li\u003e\n\u003cli\u003e\u003cb\u003eCirclips\u003c\/b\u003e\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003cp\u003e\u003cem\u003eNote: related top-end items such as a gasket kit are not included and are typically sold separately.\u003c\/em\u003e\u003c\/p\u003e\n\u003ch3\u003eWhy Choose This Aftermarket Replacement?\u003c\/h3\u003e\n\u003cul\u003e\n\u003cli\u003e\n\u003cb\u003eDirect-Fit Compatibility:\u003c\/b\u003e Engineered to drop in on Yamaha YFM350 top ends, preserving the intended clearance, pin diameter, and ring grooves when used with the proper supporting parts.\u003c\/li\u003e\n\u003cli\u003e\n\u003cb\u003eOEM Cross-Reference:\u003c\/b\u003e Uses established OEM references for reliable verification during ordering and reassembly.\u003c\/li\u003e\n\u003cli\u003e\n\u003cb\u003ePremium Materials:\u003c\/b\u003e Forged aluminum construction provides strength and durability under load, helping resist knock and wear in rugged use.\u003c\/li\u003e\n\u003cli\u003e\n\u003cb\u003eDisplacement Upgrade:\u003c\/b\u003e Oversize bore (+1.50 mm) increases displacement to boost mid-range torque and throttle response.\u003c\/li\u003e\n\u003cli\u003e\n\u003cb\u003ePerformance Restoration:\u003c\/b\u003e Restores lost power from worn rings, piston skirt wear, and compression leaks in the top end.\u003c\/li\u003e\n\u003cli\u003e\n\u003cb\u003eTrail- and Farm-Ready Reliability:\u003c\/b\u003e Built to endure off-road conditions, with precise machining and compatibility with standard wear items used in field maintenance.\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003ch3\u003eInstallation Notes:\u003c\/h3\u003e\n\u003cul\u003e\n\u003cli\u003eVerify the cylinder bore is properly prepared for a +1.50 mm oversize piston, including honing or boring per manufacturer guidelines.\u003c\/li\u003e\n\u003cli\u003eMeasure piston ring end gaps and ensure correct ring orientation before installation; use the correct gap spec for the OS size and compression target.\u003c\/li\u003e\n\u003cli\u003eLubricate the piston skirt and rings with clean engine oil before assembly to reduce initial wear on start-up.\u003c\/li\u003e\n\u003cli\u003eInstall wrist pin and circlips with the piston oriented to match the engine’s intake\/exhaust timing and rod orientation.\u003c\/li\u003e\n\u003cli\u003eCheck that all mating surfaces (cylinder head, base gasket, and head gasket) are clean, undamaged, and compatible with the oversize bore.\u003c\/li\u003e\n\u003cli\u003eFollow the engine service manual for general top-end torque guidance and final assembly checks; verify oil passages and cooling clearance after assembly.\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003ch3\u003eWhy Upgrade?\u003c\/h3\u003e\n\u003cp\u003eOperating with a worn or undersized piston kit can lead to compression loss, reduced power, and accelerated wear in the top end, especially under load on trails or farms. Upgrading to the OS 1.50 piston kit restores compression and displacement, delivering consistent power delivery, improved mid-range torque, and renewed reliability for demanding uses. The result is a more responsive, durable engine that performs like new under practical conditions.\u003c\/p\u003e\n\u003c\/div\u003e","brand":"ATV City","offers":[{"title":"Default Title","offer_id":57319261307254,"sku":"190.40005-6","price":124.99,"currency_code":"GBP","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0971\/0302\/0406\/files\/image_2026-02-25_213742958.png?v=1774886192","url":"https:\/\/dgtagri.co.uk\/products\/piston-kit-yamaha-yfm-350-big-bear-raptor-bruin-grizzly-os-1-50","provider":"DGT Agri","version":"1.0","type":"link"}