Water Pump Impeller Kit – Fits Yamaha F50A 4-Stroke (Replaces Yamaha 6BG-W0078-01-00, Sierra 18-3434)
Water Pump Impeller Kit – Fits Yamaha F50A 4-Stroke (Replaces Yamaha 6BG-W0078-01-00, Sierra 18-3434) is backordered and will ship as soon as it is back in stock.
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Delivery and Shipping
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Water Pump Impeller Kit – Fits Yamaha F50A 4-Stroke (Replaces Yamah...
Water Pump Impeller Kit – Fits Yamaha F50A 4-Stroke (Replaces Yamaha 6BG-W0078-01-00, Sierra 18-3434) is backordered and will ship as soon as it is back in stock.
Product Details
This Water Pump Impeller Kit provides a complete solution for servicing the water pump on Yamaha 4-stroke 40–50 HP outboards, including models F40, F50A (1991–2007), F30LA, and F40LA. It is designed to restore cooling system performance and prevent engine overheating.
It serves as a direct replacement for Yamaha part numbers 6BG-W0078-01-00 and 6BG-W0078-00-00, as well as aftermarket equivalents Sierra 18-3434, JLM YHJB-6BG, and SeaSierra 63DW007800.
- Designed for installation in the lower unit/gear case.
- The kit includes the impeller, impeller key, and all necessary gaskets for a complete repair.
- Restores cooling system efficiency to factory specifications.
Part Number Matrix
Use this matrix to confirm equivalent references across OEM and aftermarket.
| Brand | Part Number |
|---|---|
| Yamaha | 6BG-W0078-01-00 |
| Yamaha | 6BG-W0078-00-00 |
| Sierra | 18-3434 |
| JLM | YHJB-6BG |
| SeaSierra | 63DW007800 |
Engine & Model Compatibility
Confirm your engine model/year in the table below.
This kit is designed for a range of Yamaha 4-stroke and select 2-stroke outboard models. Please verify your specific engine against the details provided.
| Brand | Model | Rated HP | Stroke | Years | OEM Part No. | Notes |
|---|---|---|---|---|---|---|
| Yamaha | F50A | 50 | 4-Stroke | 1991–2007 | 6BG-W0078-01-00 | Included in Yamaha Maintenance Kit |
| Yamaha | F40B | 40 | 4-Stroke | 6BG-W0078-01-00 | - | |
| Yamaha | F30LA | 30 | 4-Stroke | 6BG-W0078-01-00 | - | |
| Yamaha | F40LA | 40 | 4-Stroke | 6BG-W0078-01-00 | - | |
| Yamaha | E40X, 40X | 40 | 2-Stroke | 6BG-W0078-01-00 | Also fits some 2-stroke models | |
| Yamaha | F25B | 25 | 4-Stroke | 6BG-W0078-01-00 | - |
Technical Specs
- Product Type
- Water Pump Impeller Repair Kit
- Installation
- Lower Unit/Gear Case
- Other Technical Attributes
- Includes impeller key and necessary gaskets
- Warranty
- Varies by manufacturer
What’s in the Box
- 1 x Water Pump Repair Kit (6BG-W0078-01-00)
- 1 x Impeller (6H4-44352-02)
- Impeller Key
- Necessary Gaskets and O-rings
Installation Notes
- Disconnect the negative battery cable for safety.
- Drain the gearcase oil into a suitable container.
- Shift the outboard into neutral and remove the shift rod connector bolt or pin.
- Unbolt and carefully lower the gearcase (lower unit) from the outboard's midsection.
- Remove the water pump housing bolts and lift the housing off the driveshaft.
- Remove the old impeller, woodruff key, wear plate, and gaskets. Note their orientation.
- Thoroughly clean all mating surfaces, removing any old gasket material or sealant.
- Install the new gaskets, wear plate, and woodruff key onto the driveshaft.
- Slide the new impeller onto the driveshaft, turning the shaft clockwise to help seat the impeller vanes correctly inside the housing.
- Apply a light coat of marine grease to the inside of the pump cup and reinstall the housing. Tighten bolts to the manufacturer's torque specifications.
- Reassemble the lower unit to the engine, ensuring the water tube, driveshaft splines, and shift shaft are correctly aligned.
- Refill the gearcase with fresh oil. Once assembled, start the engine in water and verify a steady stream of water from the tell-tale port.
Troubleshooting & FAQ
How do I know if this kit fits my engine?
Check the "Engine & Model Compatibility" table on this page. Confirm your engine model, horsepower, and year range. If you are unsure, compare the part numbers in the "Part Number Matrix" with your service manual or original part.
What are the signs of a failing water pump impeller?
Common signs include a weak or no water stream from the "tell-tale" port, engine overheating alarms, steam from the exhaust, and reduced engine performance.
How often should I replace my water pump impeller?
As a general maintenance rule, it is recommended to inspect the impeller annually and replace it every 1-2 years or every 100-200 hours of use, depending on operating conditions (e.g., saltwater vs. freshwater, high-silt environments).
What is the difference between 6BG-W0078-01-00 and 6BG-W0078-00-00?
The part number 6BG-W0078-01-00 is a supersession, meaning it's the newer, direct replacement for the older 6BG-W0078-00-00 part number. They are functionally interchangeable for the listed applications.
Can I use this kit for a 2-stroke model?
While the primary application is for 4-stroke engines, it also fits some 2-stroke models like the Yamaha E40X and 40X as noted in the compatibility table. Always verify your specific model and part number before ordering.
OEM vs. Aftermarket?
This listing is an aftermarket replacement (not OEM). It is built to OEM-level specifications with comparable materials and manufactured in an ISO 9002 certified facility. All parts are batch-inspected for quality and consistency.
Shipping speed & cost
We ship worldwide quickly—typical transit is 5–15 days for most locations. Standard shipping is free; expedited options will appear at checkout if they are available for your region.
Warranty & returns
This product is covered by a 1-year warranty against manufacturing defects under normal use. If you encounter any issues, please contact our support team with your order details. Returns are accepted within our standard window for unused items in their original condition. See our policy page or reach out for instructions.
Safety & Important Info
- Verify images and specifications against your original part before purchase. If anything differs—even if your model appears compatible—do not order.
- This is an aftermarket replacement component, not an OEM part. Brand names and part numbers are used for identification purposes only.
- Professional installation is highly recommended for safety and to ensure a proper seal 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.
- Fast Global Fulfillment — We offer free standard delivery to most regions with an average transit time of 5–15 days.
- Manufacturer-Direct Value — Our parts deliver fair pricing without compromising on materials, quality control, or performance.
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