{"product_id":"piston-kit-yamaha-yfm-400-fb-fw-manual-os-1-50","title":"Piston Kit OS 1.50 Fits Yamaha YFM 400 FB FW 1993 to 2012 ATV OEM Replacement Quality","description":"\u003cdiv\u003e\n\u003cp\u003eThe OS 1.50 piston kit is a purpose-built aftermarket replacement designed for Yamaha YFM 400 FB and FW models produced from 1993 through 2012. This top-end kit concentrates on restoring reliable compression and power delivery after bore wear, making overhauls and performance restoration straightforward for trail, farm, and work-cycle use. With an oversize of +0.50 mm (OS 1.50), it brings worn bores back to proper diameter to reclaim factory-like throttle response and idle stability.\u003c\/p\u003e\n\u003cp\u003eEngineered for durability in demanding riding conditions, this oversize piston kit targets the common wear points of the YFM 400 top end—piston rings, bore wear, and loss of compression that dulls performance under load. Restoring the bore size and compression helps maintain steady throttle response, consistent idle, and dependable performance when climbing hills, hauling loads, or navigating rough trails. It’s a practical upgrade path when the original top end shows signs of wear and is ready for a rebuild.\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 400 FB \/ FW Manual\u003c\/td\u003e\n\u003ctd\u003e1993–2012\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003c\/tbody\u003e\n\u003c\/table\u003e\n\u003ch3\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\u003eNot provided\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eType\u003c\/td\u003e\n\u003ctd\u003ePiston Kit OS 1.50 (0.50 mm oversize)\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 400 FB\/FW Manual (1993–2012)\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eMaterial\u003c\/td\u003e\n\u003ctd\u003ePiston kit components manufactured to aftermarket replacement quality standards\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eOversize \/ Bore Size\u003c\/td\u003e\n\u003ctd\u003e+0.50 mm (OS 1.50) — intended for overbore applications to restore bore size\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\u003eTop-End Focus\u003c\/td\u003e\n\u003ctd\u003eTop-end rebuild compatible; designed for reliable power restoration\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003c\/tbody\u003e\n\u003c\/table\u003e\n\u003ch3\u003e\u003c\/h3\u003e\n\u003ch3\u003eOEM \u0026amp; Aftermarket Cross-Reference Information\u003c\/h3\u003e\n\u003ctable\u003e\n\u003cthead\u003e\n\u003ctr\u003e\n\u003cth\u003ePart Number\u003c\/th\u003e\n\u003cth\u003eBrand \/ Type\u003c\/th\u003e\n\u003cth\u003eCross-Reference Notes\u003c\/th\u003e\n\u003c\/tr\u003e\n\u003c\/thead\u003e\n\u003ctbody\u003e\n\u003ctr\u003e\n\u003ctd\u003eNot provided\u003c\/td\u003e\n\u003ctd\u003eAftermarket Replacement\u003c\/td\u003e\n\u003ctd\u003eNo OEM cross-reference part number provided for this specific OS 1.50 kit; designed as a direct oversize replacement for Yamaha YFM 400 FB\/FW (1993–2012).\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eOS 1.50 (YFM 400 OS)\u003c\/td\u003e\n\u003ctd\u003eAftermarket Replacement\u003c\/td\u003e\n\u003ctd\u003eCross-reference notes align with standard +0.50 mm oversize piston kits used on Yamaha YFM 400 family models; verify bore suitability before install.\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003c\/tbody\u003e\n\u003c\/table\u003e\n\u003ch3\u003e\u003c\/h3\u003e\n\u003ch3\u003eWhat's Included\u003c\/h3\u003e\n\u003cp\u003eThe box includes the core piston kit components required for a top-end rebuild on the YFM 400, specifically:\u003c\/p\u003e\n\u003cul\u003e\n\u003cli\u003e\u003cb\u003ePiston\u003c\/b\u003e\u003c\/li\u003e\n\u003cli\u003e\u003cb\u003ePiston Rings\u003c\/b\u003e\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: Top-end gasket set, seals, and mounting hardware are not included in this kit and should be sourced separately as part of a complete overhaul.\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 Precisely sized for Yamaha YFM 400 FB\/FW Manual models (1993–2012), enabling a straightforward top-end rebuild without guesswork.\u003c\/li\u003e\n\u003cli\u003e\n\u003cb\u003eOEM Cross-Reference Potential:\u003c\/b\u003e While OEM part numbers are not provided here, the OS 1.50 oversize design mirrors common Yamaha oversize specs used for top-end restoration on the YFM 400 family.\u003c\/li\u003e\n\u003cli\u003e\n\u003cb\u003ePremium Materials \u0026amp; Design Intent:\u003c\/b\u003e Engineered to withstand the heat and load of a 4-stroke top end, with an oversize bore intended to restore compression and power after bore wear.\u003c\/li\u003e\n\u003cli\u003e\n\u003cb\u003ePerformance Restoration:\u003c\/b\u003e Restores throttle response, idle stability, and under-load power that’s typical of a well-tuned top end after rebuilding the cylinder.\u003c\/li\u003e\n\u003cli\u003e\n\u003cb\u003eCost-Effective Route:\u003c\/b\u003e A practical alternative to OEM top-end components, offering reliable performance restoration at a lower price point.\u003c\/li\u003e\n\u003cli\u003e\n\u003cb\u003eTrail- and Farm-Ready Durability:\u003c\/b\u003e Built to handle the rough duty cycles of trail riding and everyday work use, returning consistent performance across a variety of conditions.\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003ch3\u003eInstallation Notes:\u003c\/h3\u003e\n\u003cul\u003e\n\u003cli\u003e\n\u003cb\u003eBore Inspection First:\u003c\/b\u003e Inspect the cylinder bore for scoring or out-of-round wear; if worn, plan a proper overbore to accept the +0.50 mm oversize piston kit.\u003c\/li\u003e\n\u003cli\u003e\n\u003cb\u003eCleanliness is Critical:\u003c\/b\u003e Thoroughly clean all oil passages, gallery openings, and seating surfaces to ensure optimal seal and ring seating during initial run-in.\u003c\/li\u003e\n\u003cli\u003e\n\u003cb\u003eRings and Orientation:\u003c\/b\u003e Install new rings with correct orientation and ensure end gaps meet the manufacturer’s guidance for your specific bore size.\u003c\/li\u003e\n\u003cli\u003e\n\u003cb\u003eWrist Pin \u0026amp; Circlips:\u003c\/b\u003e Install the wrist pin and circlips with care; verify that circlip grooves are clean and seated to prevent pin retention issues.\u003c\/li\u003e\n\u003cli\u003e\n\u003cb\u003eTop-End Gasket Plan:\u003c\/b\u003e Use a complete top-end gasket kit (not included) to ensure proper sealing between the cylinder, head, and intake\/exhaust interfaces.\u003c\/li\u003e\n\u003cli\u003e\n\u003cb\u003eBearing Surfaces \u0026amp; Fasteners:\u003c\/b\u003e Reuse only compatible fasteners per torque specs and replace any worn bearing surfaces as part of the full top-end refresh.\u003c\/li\u003e\n\u003cli\u003e\n\u003cb\u003eBreak-In Procedure:\u003c\/b\u003e After installation, perform a proper break-in with light throttle for the first 20–30 minutes, avoiding high-load hammering until stable idle and smooth revs are confirmed.\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003ch3\u003eWhy Upgrade?\u003c\/h3\u003e\n\u003cp\u003eRunning a worn top end on a Yamaha YFM 400 FB\/FW can lead to compression loss, reduced throttle response, and uneven idle, especially under load. By upgrading to this OS 1.50 oversize piston kit, you restore bore size and compression, returning reliable power delivery and idle stability for everyday work and trail riding.\u003c\/p\u003e\n\u003c\/div\u003e","brand":"ATV City","offers":[{"title":"Default Title","offer_id":57319261471094,"sku":"190.40006-6","price":126.67,"currency_code":"GBP","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0971\/0302\/0406\/files\/image_2026-02-25_213005487.png?v=1772055013","url":"https:\/\/dgtagri.co.uk\/products\/piston-kit-yamaha-yfm-400-fb-fw-manual-os-1-50","provider":"DGT Agri","version":"1.0","type":"link"}