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

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

This water pump impeller repair kit is designed for Yamaha 2-stroke outboards, including 40 HP models from 1984–1994 and various 50 HP models produced between 1984 and 1996. It provides all necessary components for a complete and reliable water pump service to maintain engine cooling performance.

It serves as a direct replacement for Yamaha OEM part numbers 6H4-W0078-00-00, 6H4-W0078-01-00, and 6H4-W0078-A0-00, ensuring a precise fit and straightforward installation.

• Installation Type: Direct OEM-style replacement
• Impeller Material: High-strength, heat-resistant neoprene for durability and consistent flow.
• Complete Kit: Includes a new impeller, wear plate, insert cup, gaskets, bolts, and other hardware for a full rebuild.

Part Number Cross-Reference

Use this table to confirm equivalent part numbers across OEM and aftermarket brands.

Compatible Engine Models

Confirm your engine model/year in the table below. For Yamaha owners, here’s a guide to help you identify your engine’s serial/model: Yamaha Serial Number Guide. You can also review exploded diagrams to verify part numbers: Yamaha Parts Diagrams & Catalog.

Technical Specifications

Package Contents

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

Installation Guide

1. Safety First: Disconnect the battery and spark plug leads before beginning work.
2. Drain Gearcase Oil: Place a drain pan under the lower unit and remove the drain and vent screws to drain the gearcase oil.
3. Remove Lower Unit: Unbolt the lower unit (gearcase) from the engine's midsection. Be prepared to support its weight.
4. Access the Pump: With the lower unit removed, unbolt and remove the water pump housing to access the impeller.
5. Remove Old Components: Take out the old impeller, gaskets, wear plate, and insert cup. Note the orientation of the impeller vanes.
6. Clean and Inspect: Thoroughly clean all surfaces of the housing and lower unit. Check the housing for cracks, warping, or scoring.
7. Install New Parts: Install the new components from the kit. Lightly grease the new impeller and insert cup. Ensure the impeller vanes are oriented correctly (typically by turning the driveshaft clockwise during installation).
8. Reassemble Pump: Secure the new water pump housing with the new gasket and bolts, tightening them to the manufacturer's specified torque.
9. Reattach Lower Unit: Reinstall the lower unit, ensuring the driveshaft and water tube align correctly.
10. Refill Gearcase Oil: Pump fresh gearcase oil into the lower unit through the drain screw hole until it flows out of the vent hole. Reinstall the vent and drain screws.
11. Final Checks: Reconnect the spark plug leads and battery. Start the engine using a water supply (flushing muffs) and verify that water is exiting the tell-tale port, indicating a working pump.

Troubleshooting & FAQ

How do I confirm this kit fits my engine?
Check your engine's model, HP, and year against the "Compatible Engine Models" table above. Cross-reference your existing part number with the numbers listed in the "Part Number Cross-Reference" section for confirmation.

What are the signs of a failing water pump impeller?
Common signs include a weak or non-existent water stream from the "tell-tale" outlet, engine overheating alarms, or a melted water pump housing. The flexible neoprene impeller can become brittle and cracked over time, reducing its pumping efficiency.

How often should I replace the water pump impeller?
For preventative maintenance, it is recommended to inspect and/or replace the water pump impeller every 100 operating hours or at least once a year, whichever comes first. This is especially important if you operate in saltwater or sandy/silty conditions.

OEM vs. Aftermarket?
This listing is an aftermarket replacement part (not an OEM component). We build to OEM specifications using comparable-grade materials. Production is done in an ISO9002-certified facility, and each batch is inspected for consistent performance.

How fast do you ship and how much does it cost?
We offer fast global shipping—typically 5–15 days worldwide—and standard shipping is free. Expedited options are available at checkout depending on your location.

What is your warranty and return policy?
This product includes a 1-year warranty against manufacturing defects under normal use. If something goes wrong, contact our support team with your order details. Returns are accepted within our standard return window (unused & in original condition); please see our policy page or reach out for instructions.

Important Notes

• Verify that the product images and specifications match your original part. If discrepancies exist—even if your model is listed—do not proceed with the purchase.
• This product is an aftermarket replacement part and is not an OEM component.
• Professional installation is recommended to ensure safety and optimal performance.

Why Choose JLM MARINE?

• Quality Assured: As a trusted manufacturer for over 20 years, we supply top marine brands globally.
• Fast Global Shipping: Free delivery worldwide in 5–15 days.
• Direct from Manufacturer: Competitive pricing without compromising quality.