{"product_id":"piston-kit-yamaha-yfm-yfb-250-os-1-00-timberwolf-beartracker-bruin","title":"OS 1.00 Piston Kit for Yamaha YFM 250 and YFB 250 ATV OEM Fits 1989-2001 2005-2006","description":"\u003cdiv\u003e\n\u003cp\u003eRestore peak compression and dependable power to Yamaha YFM\/YFB 250 ATVs with the OS 1.00 Piston Kit. This oversize bore kit is engineered for Timberwolf, Bear Tracker, and Bruin models, covering 1989–2001 and 2005–2006, delivering a +1.00 mm bore to compensate wear and reclaim factory-like response. The kit arrives as a complete top-end refresh package, designed for a straightforward install so you can hit the trail or farm hard without lengthy downtime.\u003c\/p\u003e\n\u003cp\u003eOver time, piston-ring wear, bore taper, and ring-land scuffing sap compression and throttle response, especially under heavy trail work or plowing. The OS 1.00 piston kit targets these wear points with a forged aluminum piston and a full ring-set, wrist pin, and circlips to restore compression, heat tolerance, and consistent power. Built as an all-in-one aftermarket replacement, it delivers reliable, repeatable performance in demanding Yamaha YFM\/YFB 250 applications.\u003c\/p\u003e\n\u003ch3\u003eComprehensive Vehicle Fitment\u003c\/h3\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\u003eYFM 250 Bear Tracker\u003c\/td\u003e\n\u003ctd\u003e1989–2001\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eYamaha\u003c\/td\u003e\n\u003ctd\u003eYFB 250 Timberwolf\u003c\/td\u003e\n\u003ctd\u003e1989–2001\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eYamaha\u003c\/td\u003e\n\u003ctd\u003eYFM 250 Bruin\u003c\/td\u003e\n\u003ctd\u003e2005–2006\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\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\u003e4BD-11631-00-Y0\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eType\u003c\/td\u003e\n\u003ctd\u003ePiston Kit OS 1.00 (Oversized)\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\/YFB 250 engines (Timberwolf, Bear Tracker, Bruin) — 1989–2001 and 2005–2006\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003ePiston Material\u003c\/td\u003e\n\u003ctd\u003eForged aluminum\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eBore Size (Oversize)\u003c\/td\u003e\n\u003ctd\u003e+1.00 mm (72.00 mm)\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eIncludes\u003c\/td\u003e\n\u003ctd\u003ePiston, rings, wrist pin, and circlips\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: 21.8412%;\"\u003ePart Number\u003c\/th\u003e\n\u003cth style=\"width: 22.3053%;\"\u003eBrand \/ Type\u003c\/th\u003e\n\u003cth style=\"width: 55.1315%;\"\u003eCross-Reference Notes\u003c\/th\u003e\n\u003c\/tr\u003e\n\u003c\/thead\u003e\n\u003ctbody\u003e\n\u003ctr\u003e\n\u003ctd style=\"width: 21.8412%;\"\u003e4BD-11631-00-Y0\u003c\/td\u003e\n\u003ctd style=\"width: 22.3053%;\"\u003eYamaha OEM (Reference)\u003c\/td\u003e\n\u003ctd style=\"width: 55.1315%;\"\u003eOriginal equipment reference for YFM\/YFB 250 engines; used for cross-checking aftermarket oversize kits\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd style=\"width: 21.8412%;\"\u003eOS 1.00 Piston Kit\u003c\/td\u003e\n\u003ctd style=\"width: 22.3053%;\"\u003eAftermarket Replacement\u003c\/td\u003e\n\u003ctd style=\"width: 55.1315%;\"\u003eOversize +1.00 mm kit designed to replace the OEM reference; direct-fit alternative\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\u003eAll essential components for a complete top-end refresh are included.\u003c\/p\u003e\n\u003cul\u003e\n\u003cli\u003e\u003cstrong\u003ePiston\u003c\/strong\u003e\u003c\/li\u003e\n\u003cli\u003e\u003cstrong\u003eRings\u003c\/strong\u003e\u003c\/li\u003e\n\u003cli\u003e\u003cstrong\u003eWrist Pin\u003c\/strong\u003e\u003c\/li\u003e\n\u003cli\u003e\u003cstrong\u003eCirclips\u003c\/strong\u003e\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003cp\u003e\u003cem\u003eRelated gaskets, seals, and top-end hardware are not included and are typically purchased separately.\u003c\/em\u003e\u003c\/p\u003e\n\u003ch3\u003eWhy Choose This Aftermarket Replacement?\u003c\/h3\u003e\n\u003cul\u003e\n\u003cli\u003e\n\u003cstrong\u003eDirect-Fit Compatibility\u003c\/strong\u003e for Yamaha YFM\/YFB 250 engines ensures straightforward installation with proper bore and ring alignment.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eOEM Cross-Reference\u003c\/strong\u003e provides clear alignment with Yamaha’s original part numbers while delivering a ready aftermarket alternative.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003ePremium Materials\u003c\/strong\u003e—forged aluminum piston delivers strength, durability, and heat resistance in demanding riding conditions.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eOversized Bore (+1.00 mm)\u003c\/strong\u003e to restore compression and power after wear, extending engine life between rebuilds.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eAll-in-One Top-End Refresh\u003c\/strong\u003e—includes piston, rings, wrist pin, and circlips for a complete, field-ready package.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eReliability in Tough Terrain\u003c\/strong\u003e—engineered to withstand trail riding, work duty, and farm chores with consistent performance.\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003ch3\u003eInstallation Notes:\u003c\/h3\u003e\n\u003cul\u003e\n\u003cli\u003eInspect the cylinder bore for scoring and taper; verify bore size is within oversize kit specifications before installation.\u003c\/li\u003e\n\u003cli\u003eUse a proper ring compressor to install the piston; ensure rings are oriented correctly and gaps are staggered per OEM guidelines.\u003c\/li\u003e\n\u003cli\u003eLubricate the piston, rings, and wrist pin with assembly lube before final assembly to prevent dry-start wear.\u003c\/li\u003e\n\u003cli\u003eInstall the wrist pin and circlips carefully; confirm clips are fully seated and not projecting into the crankcase.\u003c\/li\u003e\n\u003cli\u003eClean all gasket surfaces and ensure the cylinder head is clear of debris; replace gaskets if reused during top-end service.\u003c\/li\u003e\n\u003cli\u003eFollow a cautious break-in procedure: throttle lightly for the first 20–30 minutes, gradually increasing RPM to seat rings and verify compression before sustained high-rpm operation.\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003ch3\u003eWhy Upgrade?\u003c\/h3\u003e\n\u003cp\u003eRunning a worn piston kit drains compression and throttle response, leading to reduced power, increased fuel consumption, and higher risk of cylinder damage. This OS 1.00 oversize kit restores proper ring seal and bore geometry, delivering reliable compression and predictable performance for trail riding and farm work. Upgrading now helps prevent sudden power loss and preserves engine longevity.\u003c\/p\u003e\n\u003c\/div\u003e","brand":"ATV City","offers":[{"title":"Default Title","offer_id":57319258161526,"sku":"190.04305","price":69.33,"currency_code":"GBP","in_stock":false}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0971\/0302\/0406\/files\/image_2026-02-25_235650515.png?v=1774886125","url":"https:\/\/dgtagri.co.uk\/products\/piston-kit-yamaha-yfm-yfb-250-os-1-00-timberwolf-beartracker-bruin","provider":"DGT Agri","version":"1.0","type":"link"}