Water Pump Impeller Kit – Fits Yamaha 2-Stroke 40/50 HP (Replaces 6H4-W0078-00-00, 6H4-W0078-01-00, 18-3429, 18-3408)

Product Details

This Water Pump Impeller Kit – Fits Yamaha 40/50 HP 2-Stroke (Replaces 6H4-W0078-00-00, 6H4-W0078-01-00) is engineered for Yamaha Marine 2-Stroke outboards, covering 40 HP models from 1984 to 1994 and various 50 HP models, including the Pro Series, manufactured between 1984 and 1996. It provides all necessary components for a complete water pump overhaul to restore engine cooling performance.

This kit serves as a direct replacement for Yamaha part numbers 6H4-W0078-00-00, 6H4-W0078-01-00, 6H4-W0078-A0-00, and interchanges with Sierra 18-3429 and 18-3408.

• Installation: Designed for direct OEM replacement with no modifications required.
• Durability: Features a neoprene rubber impeller and stainless steel components for corrosion resistance in marine environments.
• Complete Kit: Includes impeller, wear plate, gaskets, and hardware for a full service.

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 select Yamaha 2-Stroke outboard models. Please check your specific model and year against the list.

Technical Specs

Product Type

Water Pump Impeller Kit

Installation

Direct OEM replacement

Fuel Type

Gasoline (for marine engines)

Housing Material

Stainless Steel (plates), Plastic (insert cup)

Impeller Material

Neoprene Rubber

Package Dimensions

155 × 105 × 50 mm (6.1 × 4.13 × 1.97 inches)

Weight

0.22 kg (7.7 oz)

Other Attributes

Designed for corrosion resistance in marine environments

What’s in the Box

• 1 x Water Pump Impeller (6H4-44352-00)
• 1 x Key, Woodruff (90280-03024)
• 1 x Wear Plate (663-44323-00)
• 1 x Insert Cup (663-44322-00)
• 1 x Gasket (663-44315-A0)
• 1 x Gasket (663-44316-A0)
• 1 x Gasket (663-44324-A0)
• 1 x Grommet (663-44366-00)
• 2 x Bolt (97080-08045)
• 2 x Bolt (97080-08055)

Installation Notes

1. Disconnect the negative battery cable.
2. Drain the gearcase oil from the lower unit.
3. Remove the mounting bolts and detach the lower unit from the engine.
4. Unscrew the bolts on the water pump housing and carefully lift it off. Note the orientation of the old impeller vanes.
5. Remove the old impeller, woodruff key, wear plate, and gaskets.
6. Thoroughly clean the housing and mating surfaces, removing any old gasket material or corrosion.
7. Install the new wear plate, gaskets, and insert cup from the kit.
8. Place the new woodruff key in the driveshaft slot and slide the new impeller on, rotating the shaft clockwise to bend the vanes correctly.
9. Apply a light coat of marine grease to the inside of the pump cup and reinstall the housing. Torque bolts to manufacturer specifications.
10. Reinstall the lower unit, ensuring the water tube and shift shaft are correctly aligned.
11. Refill the gearcase with fresh marine gear oil.
12. Reconnect the battery and test the engine on a water supply (flusher or in water), confirming a steady stream from the tell-tale outlet.

Troubleshooting & FAQ

Safety & Important Info

• Verify images and specifications against your original part before purchase. If any detail differs—even if your model appears on the compatibility list—do not purchase.
• This is an aftermarket replacement part, not an original equipment manufacturer (OEM) component.
• Professional installation is highly recommended to ensure safety and optimal performance.

About Sea Sierra

• Pro-Grade Standards — We supply marine parts engineered to OEM-level tolerances and rigorously tested for real-world reliability in harsh marine conditions.
• Fast Global Fulfillment — We offer free standard delivery to most regions with an average transit time of 5–15 days.
• Manufacturer-Direct Value — By working directly with manufacturers, we provide fair pricing without compromising on materials or quality control.