Yamaha 40–55 HP 2-Stroke Water Pump Repair Kit Without Housing – 6H4 Code (Replaces 6H4-W0078-00-00)
Yamaha 40–55 HP 2-Stroke Water Pump Repair Kit Without Housing – 6H4 Code (Replaces 6H4-W0078-00-00) is backordered and will ship as soon as it is back in stock.
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Yamaha 40–55 HP 2-Stroke Water Pump Repair Kit Without Housing – 6H...
Yamaha 40–55 HP 2-Stroke Water Pump Repair Kit Without Housing – 6H4 Code (Replaces 6H4-W0078-00-00) is backordered and will ship as soon as it is back in stock.
Product Details
This water pump repair kit without housing is designed for Yamaha 2-stroke outboard engines using the 6H4 water-pump application. It services selected 40–55 HP models and helps restore the lower-unit cooling system by replacing the impeller and related service components.
The kit is intended for Yamaha 2-stroke 40 HP, 48 HP, 50 HP, and 55 HP applications within the model and year ranges listed below. The water pump housing is not included. Confirm the engine model code, year, and required part number before ordering.
- Water pump repair service kit for Yamaha 6H4-code 2-stroke outboards.
- Includes service components for the impeller, wear surfaces, gaskets, seals, and related hardware.
- Without housing; reuse the existing housing only if it is serviceable and matches the application.
- After installation, verify proper cooling-water flow before operating the engine under load.
Part Number Matrix
The following manufacturer and aftermarket references are associated with this 6H4-code repair-kit application. Number formats and applications can vary by model year, so verify the exact requirement for your engine.
| Brand | Part Number | Application Note |
|---|---|---|
| Yamaha | 6H4-W0078-00-00 | Water pump repair kit reference |
| Yamaha | 6H4-W0078-A0-00 | Water pump repair kit reference |
| Yamaha | 6H4-W0078-01-00 | Water pump repair kit reference |
| Yamaha | 663-44311-02-00 | Water pump housing reference associated with the application; housing is not included in this kit |
| Sierra | 18-3429 | Aftermarket without-housing service-kit reference |
| Sierra | 18-3408 | Aftermarket reference associated with the 6H4 application |
Engine & Model Compatibility
Compatibility is limited to Yamaha 2-stroke outboards using the 6H4 code. Match the complete model designation and manufacturing year before installation.
| Brand | Engine Family | Rated HP | Stroke | Years | Code |
|---|---|---|---|---|---|
| Yamaha | 40 HP outboards | 40 | 2-Stroke | 1984–1987; 1992–1994 | 6H4 |
| Yamaha | 48 HP outboards | 48 | 2-Stroke | 1995–2000 | 6H4 |
| Yamaha | 50 HP outboards | 50 | 2-Stroke | 1984–1987; 1992–1994 | 6H4 |
| Yamaha | 55 HP outboards | 55 | 2-Stroke | 1989–1995 | 6H4 |
Technical Specs
- Product Type
- Water pump repair service kit
- Housing
- Not included
- Engine Type
- Yamaha 2-stroke outboard
- Application Code
- 6H4
- Rated Power Range
- 40–55 HP, subject to the model and year conditions listed above
- Installation
- Replacement service installation; inspect the existing housing before reuse
What’s in the Box
This is a repair kit supplied without the water pump housing. The service contents are intended to include the following component types:
- Water pump impeller
- Impeller key
- Insert cup
- Wear plate
- Water pump gaskets, including wear-plate sealing gaskets
- Water seal
- Related pump bolts and service hardware
Not included: water pump housing. Do not assume that a housing, lower-unit assembly, gearcase oil, or engine-specific fasteners are included unless shown in the package received.
Installation Notes
- Confirm the engine model, year, 6H4 code, and required water-pump part number before disassembly.
- Disconnect the battery and follow the engine manufacturer's safety procedures.
- Remove the lower unit according to the service-manual procedure for your specific Yamaha model.
- Remove the existing water-pump components and note the orientation of the impeller, key, plates, gaskets, and seals.
- Inspect the existing housing carefully. Replace it separately if it is worn, scored, distorted, corroded, or otherwise unserviceable; this kit does not include a housing.
- Clean the mating surfaces and remove old gasket material without damaging the sealing surfaces.
- Install the new impeller, key, insert cup, wear plate, gaskets, seal, and hardware in the correct order for the engine model.
- Apply only the lubricant and sealant specified by the applicable service manual, and tighten fasteners to the manufacturer's specifications.
- Reinstall the lower unit, refill gearcase lubricant if required by the service procedure, and reconnect the battery.
- Start the engine using the correct water-supply procedure and verify a strong tell-tale stream and normal cooling operation before use.
Troubleshooting & FAQ
Does this kit include the water pump housing?
No. The company product record identifies this as a 2-stroke water pump service kit supplied without housing. Inspect your existing housing and replace it separately if necessary.
Which Yamaha engines does this kit fit?
The listed application is Yamaha 2-stroke 6H4-code outboards in the 40–55 HP range: 40 HP models from 1984–1987 and 1992–1994, 48 HP models from 1995–2000, 50 HP models from 1984–1987 and 1992–1994, and 55 HP models from 1989–1995. Verify the complete model code and part-number requirement before ordering.
Will this fit a Yamaha F40, F50, or F60 four-stroke?
No compatibility claim is made for those four-stroke models. The exact product record specifies Yamaha 2-stroke 6H4-code applications only.
What are the symptoms of a worn water-pump impeller?
Common symptoms include a weak or absent tell-tale stream, overheating warnings, elevated operating temperature, or damaged, brittle, cracked, or missing impeller vanes. Stop operation if the engine overheats and diagnose the cooling system before continued use.
How often should the impeller be serviced?
Inspect and service the water pump according to the engine manufacturer's maintenance schedule and operating conditions. Saltwater, sand, silt, and extended storage can accelerate wear.
Is this an OEM Yamaha part?
This listing is for a replacement service kit. It is not represented as a genuine Yamaha-branded OEM part.
What should I check before ordering?
Match the engine brand, complete model designation, manufacturing year, 6H4 application code, stroke type, and required water-pump reference. Also confirm that you need a kit without housing.
What are your shipping speeds and costs?
Standard shipping is available to most regions. Delivery times and any expedited options are calculated and displayed at checkout based on the destination.
Safety & Important Info
- Verify the complete engine model, year, 6H4 code, and part-number requirement before purchase.
- This kit is for Yamaha 2-stroke applications listed above; do not transfer the fitment to four-stroke models.
- The water pump housing is not included. Inspect the existing housing before reusing it.
- Use the correct service manual and torque specifications for the specific engine.
- Professional installation is recommended if you are not experienced with lower-unit or water-pump service.
About Sea Sierra
- Marine Replacement Parts — Service components selected for common outboard maintenance and repair applications.
- Application-Focused Listings — Fitment information is organized by engine family, stroke, horsepower, code, and year where available.
- Support Before Installation — Verify your model and required reference before ordering or beginning service.
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