{"product_id":"exhaust-flapper-valve-clamp-kit-fits-inboard-stern-drive-replaces-sierra-18-4458-glm-89260-mallory-9-44002","title":"Exhaust Flapper Valve \u0026 Clamp Kit – Fits Inboard\/Stern Drive (Replaces Sierra 18-4458, GLM 89260, Mallory 9-44002)","description":"\u003cstyle\u003e\n  \/* Outer container allows horizontal scrolling (with iOS momentum) *\/\n  .ss-table-wrap { overflow-x:auto; -webkit-overflow-scrolling:touch; }\n\n  \/* Base table styles *\/\n  table.ss-table { width:100%; border-collapse:collapse; min-width:640px; }\n  table.ss-table th, table.ss-table td {\n    padding:10px 12px; border:1px solid #e5e7eb; text-align:left; vertical-align:top;\n  }\n\n  \/* Key: prevent wrapping, word breaks, and vertical text in headers *\/\n  table.ss-table th {\n    white-space:nowrap;       \/* Do not wrap *\/\n    word-break:normal;        \/* Don’t break words *\/\n    letter-spacing:normal;    \/* Prevent theme styles from stretching letters *\/\n    font-weight:600;\n    background:#f8fafc;\n  }\n\n  \/* Small screen optimization *\/\n  @media (max-width:480px){\n    table.ss-table th, table.ss-table td { padding:8px 10px; font-size:14px; }\n  }\n\u003c\/style\u003e\n\u003csection\u003e\n\u003ch2\u003eProduct Details\u003c\/h2\u003e\n\u003cp\u003eThis \u003cstrong\u003eExhaust Flapper Valve \u0026amp; Clamp Kit – Fits 5\" \u0026amp; 6\" OD Exhaust Pipes\u003c\/strong\u003e is engineered to prevent water from entering the engine through exhaust thru-hulls during low-speed operation, stopping, or reversing. It is designed for a broad range of inboard and stern drive applications using either 5-inch or 6-inch outside diameter exhaust pipes.\u003c\/p\u003e\n\u003cp\u003eIt serves as a direct replacement for Sierra 18-4458, GLM 89260, and Mallory 9-44002.\u003c\/p\u003e\n\u003cul\u003e\n\u003cli\u003eInstalls externally via a clamp-on connection. Note: fitting to a 5\" pipe requires two 45° cuts.\u003c\/li\u003e\n\u003cli\u003eConstructed from weather-resistant EPDM rubber with a UV stabilizer for durability in marine environments.\u003c\/li\u003e\n\u003cli\u003eKit includes two flapper valves and two marine-grade SS316 stainless steel clamps for a complete installation.\u003c\/li\u003e\n\u003c\/ul\u003e\n\n\u003ch2\u003ePart Number Matrix\u003c\/h2\u003e\n\u003cp\u003eUse this matrix to confirm equivalent references across OEM and aftermarket.\u003c\/p\u003e\n\u003cdiv class=\"ss-table-wrap\"\u003e\n  \u003ctable class=\"ss-table\" aria-label=\"Part Number Matrix\"\u003e\n    \u003cthead\u003e\n      \u003ctr\u003e\n        \u003cth\u003eBrand\u003c\/th\u003e\n        \u003cth\u003ePart Number\u003c\/th\u003e\n      \u003c\/tr\u003e\n    \u003c\/thead\u003e\n    \u003ctbody\u003e\n      \u003ctr\u003e\n        \u003ctd\u003eSierra\u003c\/td\u003e\n        \u003ctd\u003e18-4458\u003c\/td\u003e\n      \u003c\/tr\u003e\n      \u003ctr\u003e\n        \u003ctd\u003eGLM\u003c\/td\u003e\n        \u003ctd\u003e89260\u003c\/td\u003e\n      \u003c\/tr\u003e\n      \u003ctr\u003e\n        \u003ctd\u003eMallory\u003c\/td\u003e\n        \u003ctd\u003e9-44002\u003c\/td\u003e\n      \u003c\/tr\u003e\n       \u003ctr\u003e\n        \u003ctd\u003eSerria\/Sierra\u003c\/td\u003e\n        \u003ctd\u003e18-4458\u003c\/td\u003e\n      \u003c\/tr\u003e\n    \u003c\/tbody\u003e\n  \u003c\/table\u003e\n\u003c\/div\u003e\n\n\u003ch2\u003eEngine \u0026amp; Model Compatibility\u003c\/h2\u003e\n\u003cp\u003eConfirm your engine model\/year in the table below.\u003c\/p\u003e\n\u003cdiv class=\"ss-table-wrap\"\u003e\n  \u003ctable class=\"ss-table\" aria-label=\"Engine \u0026amp; Model Compatibility\"\u003e\n    \u003cthead\u003e\n      \u003ctr\u003e\n        \u003cth\u003eBrand\u003c\/th\u003e\n        \u003cth\u003eModel\u003c\/th\u003e\n        \u003cth\u003eRated HP\u003c\/th\u003e\n        \u003cth\u003eStroke\u003c\/th\u003e\n        \u003cth\u003eYears\u003c\/th\u003e\n        \u003cth\u003eOEM Part No.\u003c\/th\u003e\n        \u003cth\u003eNotes\u003c\/th\u003e\n      \u003c\/tr\u003e\n    \u003c\/thead\u003e\n    \u003ctbody\u003e\n      \u003ctr\u003e\n        \u003ctd\u003eChris-Craft\u003c\/td\u003e\n        \u003ctd\u003eInboard Engines\u003c\/td\u003e\n        \u003ctd\u003eVarious\u003c\/td\u003e\n        \u003ctd\u003e4-Stroke\u003c\/td\u003e\n        \u003ctd\u003e\u003c\/td\u003e\n        \u003ctd\u003e\u003c\/td\u003e\n        \u003ctd\u003eFor 5\" \u0026amp; 6\" exhaust pipes\u003c\/td\u003e\n      \u003c\/tr\u003e\n      \u003ctr\u003e\n        \u003ctd\u003eChrysler\u003c\/td\u003e\n        \u003ctd\u003eInboards\u003c\/td\u003e\n        \u003ctd\u003eVarious\u003c\/td\u003e\n        \u003ctd\u003e4-Stroke\u003c\/td\u003e\n        \u003ctd\u003e\u003c\/td\u003e\n        \u003ctd\u003e\u003c\/td\u003e\n        \u003ctd\u003eFor 5\" \u0026amp; 6\" exhaust pipes\u003c\/td\u003e\n      \u003c\/tr\u003e\n      \u003ctr\u003e\n        \u003ctd\u003eCrusader\u003c\/td\u003e\n        \u003ctd\u003eInboards\u003c\/td\u003e\n        \u003ctd\u003eVarious\u003c\/td\u003e\n        \u003ctd\u003e4-Stroke\u003c\/td\u003e\n        \u003ctd\u003e\u003c\/td\u003e\n        \u003ctd\u003e\u003c\/td\u003e\n        \u003ctd\u003eFor 5\" \u0026amp; 6\" exhaust pipes\u003c\/td\u003e\n      \u003c\/tr\u003e\n      \u003ctr\u003e\n        \u003ctd\u003eMercury\/Mariner\u003c\/td\u003e\n        \u003ctd\u003eInboard\/Outboard\u003c\/td\u003e\n        \u003ctd\u003eVarious\u003c\/td\u003e\n        \u003ctd\u003e4-Stroke\u003c\/td\u003e\n        \u003ctd\u003e\u003c\/td\u003e\n        \u003ctd\u003e\u003c\/td\u003e\n        \u003ctd\u003eFor 5\" \u0026amp; 6\" exhaust pipes\u003c\/td\u003e\n      \u003c\/tr\u003e\n      \u003ctr\u003e\n        \u003ctd\u003ePleasurecraft (PCM)\u003c\/td\u003e\n        \u003ctd\u003eWaukesha\u003c\/td\u003e\n        \u003ctd\u003eVarious\u003c\/td\u003e\n        \u003ctd\u003e4-Stroke\u003c\/td\u003e\n        \u003ctd\u003e\u003c\/td\u003e\n        \u003ctd\u003e\u003c\/td\u003e\n        \u003ctd\u003eFor 5\" \u0026amp; 6\" exhaust pipes\u003c\/td\u003e\n      \u003c\/tr\u003e\n    \u003c\/tbody\u003e\n  \u003c\/table\u003e\n\u003c\/div\u003e\n\n\u003ch2\u003eTechnical Specs\u003c\/h2\u003e\n\u003cdl\u003e\n  \u003cdt\u003eProduct Type\u003c\/dt\u003e\n\u003cdd\u003eExhaust Guard \/ Flapper Valve \u0026amp; Clamp Kit\u003c\/dd\u003e\n  \u003cdt\u003eInstallation\u003c\/dt\u003e\n\u003cdd\u003eExternal; 5\" requires two 45° cuts\u003c\/dd\u003e\n  \u003cdt\u003eConnection\u003c\/dt\u003e\n\u003cdd\u003eClamp-on to exhaust pipe\u003c\/dd\u003e\n  \u003cdt\u003eHousing Material\u003c\/dt\u003e\n\u003cdd\u003eWeather resistant EPDM rubber with UV stabilizer\u003c\/dd\u003e\n  \u003cdt\u003eHousing Color\u003c\/dt\u003e\n\u003cdd\u003eBlack\u003c\/dd\u003e\n  \u003cdt\u003eDimensions\u003c\/dt\u003e\n\u003cdd\u003eFits 5\" \u0026amp; 6\" OD pipes (127mm \u0026amp; 152.4mm)\u003c\/dd\u003e\n  \u003cdt\u003eFitting Type\u003c\/dt\u003e\n\u003cdd\u003eStainless steel hose clamp\u003c\/dd\u003e\n  \u003cdt\u003eOther Technical Attributes\u003c\/dt\u003e\n\u003cdd\u003eStainless steel clamp is marine grade SS316\u003c\/dd\u003e\n  \u003cdt\u003eWarranty\u003c\/dt\u003e\n\u003cdd\u003e1 Year (YiheoZux brand) or Limited Lifetime (Sierra brand)\u003c\/dd\u003e\n\u003c\/dl\u003e\n\n\u003ch2\u003eWhat’s in the Box\u003c\/h2\u003e\n\u003cul\u003e\n  \u003cli\u003e\n\u003cspan style=\"color:#d0021b;\"\u003e2 x\u003c\/span\u003e Exhaust Guard Covers\u003c\/li\u003e\n  \u003cli\u003e\n\u003cspan style=\"color:#d0021b;\"\u003e2 x\u003c\/span\u003e Stainless Steel Hose Clamps\u003c\/li\u003e\n\u003c\/ul\u003e\n\n\u003ch2\u003eInstallation Notes\u003c\/h2\u003e\n\u003col\u003e\n  \u003cli\u003eEnsure the engine is completely cool and turned off before beginning installation.\u003c\/li\u003e\n  \u003cli\u003eIf fitting to a 5\" outside diameter exhaust pipe, carefully measure and make two 45° cuts on the rubber housing to allow it to fit snugly.\u003c\/li\u003e\n  \u003cli\u003eSlide the exhaust flapper valve over the end of the exhaust pipe outlet until it sits securely.\u003c\/li\u003e\n  \u003cli\u003ePosition the stainless steel hose clamp over the rubber housing where it meets the pipe.\u003c\/li\u003e\n  \u003cli\u003eTighten the hose clamp firmly with a screwdriver or socket wrench until the flapper is securely fastened and does not move. Do not overtighten.\u003c\/li\u003e\n\u003c\/ol\u003e\n\n\u003ch2\u003eTroubleshooting \u0026amp; FAQ\u003c\/h2\u003e\n\u003cdetails\u003e\n  \u003csummary\u003eHow do I know if this flapper valve will fit my boat?\u003c\/summary\u003e\n  \u003cp\u003eThis kit is designed for boats with inboard or stern drive engines that have a 5-inch or 6-inch outside diameter (OD) exhaust pipe. The best way to confirm fitment is to measure the OD of your boat's exhaust outlet pipe.\u003c\/p\u003e\n\u003c\/details\u003e\n\u003cdetails\u003e\n  \u003csummary\u003eHow do I install this on a 5-inch exhaust pipe?\u003c\/summary\u003e\n  \u003cp\u003eTo adapt the flapper for a 5-inch pipe, you must make two 45-degree cuts on the flexible rubber housing. This allows it to conform to the smaller pipe diameter before clamping.\u003c\/p\u003e\n\u003c\/details\u003e\n\u003cdetails\u003e\n  \u003csummary\u003eWhat is the purpose of an exhaust flapper?\u003c\/summary\u003e\n  \u003cp\u003eAn exhaust flapper acts as a one-way valve, letting exhaust gases out while preventing water from splashing back into the exhaust system and engine when the boat is stopping, docking, or operating in reverse.\u003c\/p\u003ePhone\u003c\/details\u003e\n\u003cdetails\u003e\n  \u003csummary\u003eWhen should I replace my exhaust flappers?\u003c\/summary\u003e\n  \u003cp\u003eInspect your flappers regularly for signs of wear, such as cracking, splitting, or brittleness. It is good practice to replace them every few seasons as part of preventative maintenance, or immediately if any damage is found.\u003c\/p\u003e\n\u003c\/details\u003e\n\u003cdetails\u003e\n  \u003csummary\u003eOEM vs. Aftermarket?\u003c\/summary\u003e\n  \u003cp\u003eThis listing is an aftermarket replacement (not OEM). Built to OEM-level specifications with comparable materials. Manufactured in an ISO 9002 facility, batch-inspected for consistency.\u003c\/p\u003e\n\u003c\/details\u003e\n\u003cdetails\u003e\n  \u003csummary\u003eShipping speed \u0026amp; cost?\u003c\/summary\u003e\n  \u003cp\u003eWe ship worldwide quickly—typical transit 5–15 days. Standard shipping is free; expedited options appear at checkout where available.\u003c\/p\u003e\n\u003c\/details\u003e\n\u003cdetails\u003e\n  \u003csummary\u003eWarranty \u0026amp; returns?\u003c\/summary\u003e\n  \u003cp\u003eCovered by a 1-year warranty against manufacturing defects under normal use. If issues arise, contact support with your order details. Returns are accepted within our standard window (unused \u0026amp; in original condition). See our policy page or reach out for instructions.\u003c\/p\u003e\n\u003c\/details\u003e\n\n\u003ch2\u003eSafety \u0026amp; Important Info\u003c\/h2\u003e\n\u003cul\u003e\n  \u003cli\u003eVerify images\/specifications vs your original part. If anything differs—even if your model appears compatible—do not purchase.\u003c\/li\u003e\n  \u003cli\u003eThis is an aftermarket replacement, not an OEM component.\u003c\/li\u003e\n  \u003cli\u003eProfessional installation is recommended for safety and performance.\u003c\/li\u003e\n\u003c\/ul\u003e\n\n\u003ch2\u003eAbout Sea Sierra\u003c\/h2\u003e\n\u003cul\u003e\n  \u003cli\u003e\n\u003cstrong\u003ePro-Grade Standards\u003c\/strong\u003e — We supply marine parts engineered to OEM-level tolerances and tested for real-world conditions.\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003eFast Global Fulfillment\u003c\/strong\u003e — Free standard delivery to most regions in 5–15 days.\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003eManufacturer-Direct Value\u003c\/strong\u003e — Fair pricing without compromising on materials or QC.\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003c\/section\u003e","brand":"SeaSierra","offers":[{"title":"Default Title","offer_id":50717903585595,"sku":"QM-23EF445","price":49.99,"currency_code":"USD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0826\/8673\/8747\/files\/QM-23EF445.png?v=1762937965","url":"https:\/\/seasierra.com\/products\/exhaust-flapper-valve-clamp-kit-fits-inboard-stern-drive-replaces-sierra-18-4458-glm-89260-mallory-9-44002","provider":"SeaSierra","version":"1.0","type":"link"}