{"product_id":"water-pump-repair-kit-fits-yamaha-2-stroke-40-50hp-replaces-6h4-w0078-00-00-sierra-18-3429","title":"Water Pump Repair Kit – Fits Yamaha 2-Stroke 40-50HP (Replaces 6H4-W0078-00-00, Sierra 18-3429)","description":"\u003csection\u003e\n\u003c!-- 🔧 Table Styles (include only once per page) --\u003e\n\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\n\u003ch2\u003eProduct Details\u003c\/h2\u003e\n\u003cp\u003eThis \u003cstrong\u003eWater Pump Repair Kit – Fits Yamaha 2-Stroke 40-50HP\u003c\/strong\u003e provides the essential components to restore your outboard's cooling system performance. It is designed for specific Yamaha 40HP (1984–1994), 50HP (1984–1987), Pro Series 50 (1987–1990), and P50 (1995–1996) models.\u003c\/p\u003e\n\u003cp\u003eThe kit serves as a direct replacement for multiple OEM and aftermarket part numbers, including Yamaha 6H4-W0078-00-00, 6H4-W0078-01-00, 6H4-W0078-A0-00, and Sierra 18-3429.\u003c\/p\u003e\n\u003cul\u003e\n\u003cli\u003eEngineered for direct-fit installation, matching OEM specifications.\u003c\/li\u003e\n\u003cli\u003eCompatible with marine 2-stroke outboard cooling systems.\u003c\/li\u003e\n\u003cli\u003eThe water pump housing is not included with this base kit and must be purchased separately.\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        \u003cth\u003eNotes\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\u003e6H4-W0078-00-00\u003c\/td\u003e\n        \u003ctd\u003e\u003c\/td\u003e\n      \u003c\/tr\u003e\n      \u003ctr\u003e\n        \u003ctd\u003eYamaha\u003c\/td\u003e\n        \u003ctd\u003e6H4-W0078-01-00\u003c\/td\u003e\n        \u003ctd\u003e\u003c\/td\u003e\n      \u003c\/tr\u003e\n      \u003ctr\u003e\n        \u003ctd\u003eYamaha\u003c\/td\u003e\n        \u003ctd\u003e6H4-W0078-A0-00\u003c\/td\u003e\n        \u003ctd\u003e\u003c\/td\u003e\n      \u003c\/tr\u003e\n      \u003ctr\u003e\n        \u003ctd\u003eSierra\u003c\/td\u003e\n        \u003ctd\u003e18-3429\u003c\/td\u003e\n        \u003ctd\u003eBase kit without housing.\u003c\/td\u003e\n      \u003c\/tr\u003e\n      \u003ctr\u003e\n        \u003ctd\u003eSierra\u003c\/td\u003e\n        \u003ctd\u003e18-3408\u003c\/td\u003e\n        \u003ctd\u003eReferences a kit that includes the housing.\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\u003cp\u003eThis kit is verified to fit the following Yamaha outboard models within the specified year ranges.\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\u003eYamaha\u003c\/td\u003e\n        \u003ctd\u003eOutboard\u003c\/td\u003e\n        \u003ctd\u003e40\u003c\/td\u003e\n        \u003ctd\u003e2-Stroke\u003c\/td\u003e\n        \u003ctd\u003e1984–1994\u003c\/td\u003e\n        \u003ctd\u003e6H4-W0078-00-00, 6H4-W0078-01-00, 6H4-W0078-A0-00\u003c\/td\u003e\n        \u003ctd\u003e\u003c\/td\u003e\n      \u003c\/tr\u003e\n      \u003ctr\u003e\n        \u003ctd\u003eYamaha\u003c\/td\u003e\n        \u003ctd\u003eOutboard\u003c\/td\u003e\n        \u003ctd\u003e50\u003c\/td\u003e\n        \u003ctd\u003e2-Stroke\u003c\/td\u003e\n        \u003ctd\u003e1984–1987\u003c\/td\u003e\n        \u003ctd\u003e6H4-W0078-00-00, 6H4-W0078-01-00, 6H4-W0078-A0-00\u003c\/td\u003e\n        \u003ctd\u003e\u003c\/td\u003e\n      \u003c\/tr\u003e\n      \u003ctr\u003e\n        \u003ctd\u003eYamaha\u003c\/td\u003e\n        \u003ctd\u003eOutboard Pro Series 50\u003c\/td\u003e\n        \u003ctd\u003e50\u003c\/td\u003e\n        \u003ctd\u003e2-Stroke\u003c\/td\u003e\n        \u003ctd\u003e1987–1990\u003c\/td\u003e\n        \u003ctd\u003e6H4-W0078-00-00, 6H4-W0078-01-00, 6H4-W0078-A0-00\u003c\/td\u003e\n        \u003ctd\u003e\u003c\/td\u003e\n      \u003c\/tr\u003e\n      \u003ctr\u003e\n        \u003ctd\u003eYamaha\u003c\/td\u003e\n        \u003ctd\u003eOutboard P50\u003c\/td\u003e\n        \u003ctd\u003e50\u003c\/td\u003e\n        \u003ctd\u003e2-Stroke\u003c\/td\u003e\n        \u003ctd\u003e1995–1996\u003c\/td\u003e\n        \u003ctd\u003e6H4-W0078-00-00, 6H4-W0078-01-00, 6H4-W0078-A0-00\u003c\/td\u003e\n        \u003ctd\u003e\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\u003eWater Pump Repair Kit\u003c\/dd\u003e\n  \u003cdt\u003eInstallation\u003c\/dt\u003e\n\u003cdd\u003eDirect OEM replacement\u003c\/dd\u003e\n  \u003cdt\u003eHousing Material\u003c\/dt\u003e\n\u003cdd\u003eNot included in base kit (housing sold separately)\u003c\/dd\u003e\n  \u003cdt\u003eOther Technical Attributes\u003c\/dt\u003e\n\u003cdd\u003eCompatible with marine 2-stroke outboard cooling systems\u003c\/dd\u003e\n\u003c\/dl\u003e\n\n\u003ch2\u003eWhat’s in the Box\u003c\/h2\u003e\n\u003cul\u003e\n  \u003cli\u003e1 x Water Pump Impeller (6H4-44352-00)\u003c\/li\u003e\n  \u003cli\u003e1 x Woodruff Key (90280-03M03-00)\u003c\/li\u003e\n  \u003cli\u003e1 x Cartridge Outer Plate (663-44323-00)\u003c\/li\u003e\n  \u003cli\u003e1 x Insert Cup (663-44322-00)\u003c\/li\u003e\n  \u003cli\u003e1 x Gasket (663-44315-A0)\u003c\/li\u003e\n  \u003cli\u003e1 x Gasket (663-44316-A0)\u003c\/li\u003e\n  \u003cli\u003e1 x Gasket (663-44324-A0)\u003c\/li\u003e\n  \u003cli\u003e1 x Water Seal (93101-23070-00)\u003c\/li\u003e\n  \u003cli\u003e\u003cspan style=\"color:#d0021b;\"\u003e4 x Bolt (97095-08045-00)\u003c\/span\u003e\u003c\/li\u003e\n\u003c\/ul\u003e\n\n\u003ch2\u003eInstallation Notes\u003c\/h2\u003e\n\u003col\u003e\n  \u003cli\u003eDisconnect the spark plug leads and the battery for safety.\u003c\/li\u003e\n  \u003cli\u003eShift the outboard into neutral and remove the lower unit (gearcase) bolts.\u003c\/li\u003e\n  \u003cli\u003eCarefully lower the gearcase to access the water pump assembly.\u003c\/li\u003e\n  \u003cli\u003eRemove the bolts securing the water pump housing and lift it off. Note the orientation of all parts.\u003c\/li\u003e\n  \u003cli\u003eRemove the old impeller, plate, gaskets, and seals. Thoroughly clean all surfaces of debris and old gasket material.\u003c\/li\u003e\n  \u003cli\u003eInstall the new insert cup, gaskets, and outer plate from the kit.\u003c\/li\u003e\n  \u003cli\u003eInstall the new Woodruff key and slide the new impeller onto the driveshaft. Turn the shaft clockwise to seat the impeller vanes correctly.\u003c\/li\u003e\n  \u003cli\u003eApply a light coat of marine grease to the inside of the housing and reinstall it.\u003c\/li\u003e\n  \u003cli\u003eTighten the housing bolts to the manufacturer's recommended torque specification.\u003c\/li\u003e\n  \u003cli\u003eReinstall the lower unit, ensuring the driveshaft, shift shaft, and water tube are properly aligned.\u003c\/li\u003e\n  \u003cli\u003eOnce fully assembled, test the engine in water to verify proper cooling system operation.\u003c\/li\u003e\n\u003c\/ol\u003e\n\n\u003ch2\u003eTroubleshooting \u0026amp; FAQ\u003c\/h2\u003e\n\u003cdetails\u003e\n  \u003csummary\u003eHow do I confirm this kit fits my Yamaha engine?\u003c\/summary\u003e\n  \u003cp\u003eThe most reliable method is to cross-reference your engine's model and year against the \"Engine \u0026amp; Model Compatibility\" table. Additionally, you can check the part number stamped on your existing water pump components against the numbers listed in our \"Part Number Matrix.\"\u003c\/p\u003e\n\u003c\/details\u003e\n\u003cdetails\u003e\n  \u003csummary\u003eWhat are the signs of a failing water pump?\u003c\/summary\u003e\n  \u003cp\u003eCommon symptoms include a weak or intermittent \"telltale\" water stream, engine overheating alarms, or a noticeable decrease in engine performance. A brittle, cracked, or deformed impeller is a clear sign that replacement is needed.\u003c\/p\u003e\n\u003c\/details\u003e\n\u003cdetails\u003e\n  \u003csummary\u003eHow often should the water pump impeller be replaced?\u003c\/summary\u003e\n  \u003cp\u003eAs a general maintenance guideline, the impeller should be inspected annually and replaced every 1-2 years or every 100-200 hours of operation, whichever comes first. This interval may be shorter if you frequently operate in sandy or silty water.\u003c\/p\u003e\n\u003c\/details\u003e\n\u003cdetails\u003e\n  \u003csummary\u003eDoes this kit include the water pump housing?\u003c\/summary\u003e\n  \u003cp\u003eNo, this is a base repair kit that does not include the metal or plastic housing. If your housing is cracked, warped, or heavily scored, it must be purchased separately. This kit's cross-reference (Sierra 18-3429) is for a kit without the housing.\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":50723801497915,"sku":"YY-22KY026","price":29.99,"currency_code":"USD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0826\/8673\/8747\/files\/YY-22KY026.png?v=1763032195","url":"https:\/\/seasierra.com\/products\/water-pump-repair-kit-fits-yamaha-2-stroke-40-50hp-replaces-6h4-w0078-00-00-sierra-18-3429","provider":"SeaSierra","version":"1.0","type":"link"}