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

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

This water pump impeller kit is designed for Yamaha Marine 2-Stroke 40 HP (1984–1994) and 50 HP (1984–1987, Pro Series 50 1987–1990, P50 1995–1996) outboard engines.

This kit is a direct aftermarket replacement 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.

• Installation: Direct OEM replacement designed to fit without modification.
• Materials: Includes a durable neoprene rubber impeller, stainless steel wear plates, and a plastic insert cup for corrosion resistance.
• Complete Kit: Contains all necessary gaskets, bolts, and components for a full water pump service.

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 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 Guide

1. Disconnect the battery and remove the engine cover. Shift the outboard into neutral.
2. Remove the bolts securing the lower unit to the midsection and carefully lower it from the engine.
3. Place the lower unit on a suitable workbench and locate the water pump housing on top of the gearcase.
4. Unscrew the bolts holding the water pump housing cover and slide the housing up and off the driveshaft.
5. Remove the old impeller, Woodruff key, and wear plates. Thoroughly clean all mating surfaces and remove old gasket material.
6. Install the new wear plate and gaskets. Place the new Woodruff key in its slot on the driveshaft.
7. Align the keyway on the new impeller and slide it down onto the driveshaft.
8. Install the new insert cup into the housing. Carefully lower the housing over the impeller, turning the driveshaft clockwise to help the impeller vanes fold correctly inside the cup.
9. Secure the housing with the new gaskets and bolts, tightening them to the manufacturer's specified torque.
10. Reinstall the lower unit, ensuring the driveshaft, shift shaft, and water tube are properly aligned.
11. Secure the lower unit mounting bolts.
12. Reconnect the battery and test the engine using a water supply (flushing muffs or in water) to verify strong water flow from the tell-tale outlet.

Troubleshooting & FAQ

How do I confirm this fits my engine?
To ensure compatibility, check that your engine's model and year are listed in our "Compatible Engine Models" table. This kit corresponds to Yamaha OEM part number 6H4-W0078-00-00, so cross-referencing your existing part number is also a reliable method.

What are the signs that my impeller needs to be replaced?
Common symptoms of a failing impeller include the engine overheating at idle or low speeds, a weak or intermittent water stream from the tell-tale (pee) hole, or finding cracked, brittle, or broken vanes during a visual inspection.

How often should I replace the water pump impeller?
For preventative maintenance and to ensure engine reliability, we recommend inspecting your impeller annually and replacing it every 1 to 2 years. This interval may be shorter if you operate frequently in sandy/silty water or put high hours on your engine.

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.