Water Pump Repair Kit – Fits Yamaha 2-Stroke 40/50 HP Outboards (Replaces 6H4-W0078-00-00, 6H4-W0078-A0-00)

Product Details

This Water Pump Repair Kit – Fits Yamaha 2-Stroke 40/50 HP Outboards (Replaces 6H4-W0078-00-00, 6H4-W0078-A0-00) provides all necessary components to restore your engine’s cooling system. It is designed for Yamaha 2-stroke 40 HP and 50 HP models from 1984–1994, including the P50 and Pro50 series outboard engines.

The kit serves as a direct interchange for Yamaha part numbers 6H4-W0078-00-00, 6H4-W0078-01-00, and 6H4-W0078-A0-00, as well as Sierra 18-3429 and 18-3408.

• Engineered for direct replacement, requiring standard water pump disassembly.
• Constructed from corrosion-resistant marine-grade metal alloys and durable neoprene rubber.
• Includes a complete assembly of the impeller, gaskets, seals, plates, and installation hardware.

Part Number Matrix

Use this matrix to confirm equivalent references across OEM and aftermarket.

Engine & Model Compatibility

Confirm your engine model/year in the table below.

This kit is designed for a wide range of Yamaha 40HP and 50HP 2-stroke outboards manufactured between 1984 and 1994.

Technical Specs

Product Type

Water Pump Repair Kit

Application

2-Stroke Outboard Engine Cooling System

Material

Corrosion-resistant marine-grade metal alloy and neoprene rubber

Installation

Direct replacement requiring pump disassembly

Package Dimensions

20.0 cm (L) x 14.0 cm (W) x 4.0 cm (H)

Product Dimensions

20.0 cm (L) x 14.0 cm (W) x 4.0 cm (H)

What’s in the Box

• 1 x Water Pump Impeller (6H4-44352-00-00/6H4-44352-02-00)
• 1 x Key, Woodruff (90280-03M03-00/90280-03024-00)
• 1 x Cartridge Outer Plate (663-44323-00-00)
• 1 x Insert Cup (663-44322-00-00)
• 1 x Gasket (663-44315-A0-00)
• 1 x Gasket (663-44316-A0-00)
• 1 x Gasket (663-44324-A0-00)
• 1 x Water Seal (93101-23070-00)
• 4 x Bolt (97095-08045-00)

Installation Notes

1. Disconnect the battery and remove the engine cowling.
2. Drain the lower unit gear lube.
3. Remove the lower unit (gearcase) from the outboard’s driveshaft housing.
4. Unbolt and remove the existing water pump housing. Note the orientation of all parts.
5. Remove the old impeller, gaskets, seals, and plates. Clean all mating surfaces thoroughly.
6. Install the new components from the kit in the reverse order of removal.
7. Crucially, lubricate the new impeller and insert cup with silicone grease, glycerin, or dish soap to prevent damage during the first dry start. Do not use petroleum-based lubricants.
8. Reassemble the water pump housing, ensuring all bolts are torqued to manufacturer specifications.
9. Reinstall the lower unit, refill the gear lube, and reconnect the battery.
10. Start the engine in water and verify a steady stream of water from the tell-tale port.

Troubleshooting & FAQ

Safety & Important Info

• Verify images/specifications vs your original part. If anything differs—even if your model appears compatible—do not purchase.
• This is an aftermarket replacement, not an OEM component.
• Professional installation is recommended for safety and performance.

About Sea Sierra

• Pro-Grade Standards — We supply marine parts engineered to OEM-level tolerances and tested for real-world conditions.
• Fast Global Fulfillment — Free standard delivery to most regions in 5–15 days.
• Manufacturer-Direct Value — Fair pricing without compromising on materials or QC.