Water Pump Impeller Repair Kit – Fits Yamaha 2-Stroke 40/50 HP Outboards (Replaces 6H4-W0078-00-00, 6H4-W0078-01-00, 6H4-W0078-A0-00)
Water Pump Impeller Repair Kit – Fits Yamaha 2-Stroke 40/50 HP Outboards (Replaces 6H4-W0078-00-00, 6H4-W0078-01-00, 6H4-W0078-A0-00) is backordered and will ship as soon as it is back in stock.
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Water Pump Impeller Repair Kit – Fits Yamaha 2-Stroke 40/50 HP Outb...
Water Pump Impeller Repair Kit – Fits Yamaha 2-Stroke 40/50 HP Outboards (Replaces 6H4-W0078-00-00, 6H4-W0078-01-00, 6H4-W0078-A0-00) is backordered and will ship as soon as it is back in stock.
Product Details
This aftermarket Water Pump Impeller Repair Kit is designed to service the cooling system on selected Yamaha 2-stroke 40 HP and 50 HP outboard engines. The kit is supplied without a water-pump housing and is intended for replacement of the internal water-pump service components during standard water-pump disassembly.
The kit is listed as a replacement for Yamaha references 6H4-W0078-00-00, 6H4-W0078-01-00, and 6H4-W0078-A0-00. Sierra references 18-3429 and 18-3408 may appear in cross-reference material, but these aftermarket numbers do not necessarily describe the same package configuration: Sierra 18-3408 is identified as a kit with housing, while this listing is the without-housing service-kit configuration.
- Services the water-pump cooling circuit on compatible Yamaha 2-stroke outboards.
- Includes an impeller, key, wear plate, insert cup, gaskets, water seal, and mounting bolts.
- Supplied without the water-pump housing.
- Installation requires removal and disassembly of the water-pump assembly.
Part Number Matrix
Use the following references to compare the applicable Yamaha and aftermarket service numbers. Confirm the engine model and package configuration before ordering.
| Brand | Part Number | Reference Type | Notes |
|---|---|---|---|
| Yamaha | 6H4-W0078-00-00 | OEM reference | Water-pump repair-kit reference. |
| Yamaha | 6H4-W0078-01-00 | OEM reference | Listed for compatible 1992–1993 40 HP and 50 HP applications in catalog records. |
| Yamaha | 6H4-W0078-A0-00 | OEM reference | Replacement reference for the without-housing configuration. |
| Sierra | 18-3429 | Aftermarket cross-reference | Water-pump kit reference for the Yamaha 6H4 application. |
| Sierra | 18-3408 | Aftermarket cross-reference | Catalog material identifies this number as a kit with housing; package contents may differ from this listing. |
Engine & Model Compatibility
Fitment depends on the complete engine model and year, not horsepower alone. Catalog records associate the 6H4 water-pump repair-kit family with selected Yamaha 40 HP and 50 HP 2-stroke outboards, including the model groups shown below. Always compare the original water-pump parts and engine identification before installation.
| Brand | Model or Model Group | Rated HP | Stroke | Documented Years | Applicable OEM Reference |
|---|---|---|---|---|---|
| Yamaha | 40ELN, 40ESN, 40LN, 40SN | 40 | 2-Stroke | 1984 | 6H4-W0078-00-00 |
| Yamaha | 50ETLK, 50ETLN, 50ETSK, 50ETSN | 50 | 2-Stroke | 1984 | 6H4-W0078-00-00 |
| Yamaha | 40ELK, 40ESK | 40 | 2-Stroke | 1985 | 6H4-W0078-00-00 |
| Yamaha | 40EJRQ, 40ELRQ, 40ESRQ, 40MJHQ, 40MLHQ, 40MSHQ, 40PLRQ | 40 | 2-Stroke | 1992 | 6H4-W0078-01-00 |
| Yamaha | 50EJRQ, 50ELRQ, 50TLHQ, P50TLRQ | 50 | 2-Stroke | 1992 | 6H4-W0078-01-00 |
| Yamaha | 40EJRR, 40ELRR, 40ESRR, 40MJHR, 40MLHR, 40MSHR, 40PLRR | 40 | 2-Stroke | 1993 | 6H4-W0078-01-00 |
| Yamaha | 50EJRR, 50ELRR | 50 | 2-Stroke | 1993 | 6H4-W0078-01-00 |
Technical Specs
- Product Type
- Water pump impeller repair kit
- Application
- Selected Yamaha 2-stroke 40 HP and 50 HP outboard cooling systems
- Configuration
- Without water-pump housing
- Installation
- Replacement during water-pump disassembly
- Included Hardware
- Impeller, key, insert cup, wear plate, gaskets, water seal, and bolts
What's in the Box
- 1 x Water-pump impeller
- 1 x Impeller key
- 1 x Insert cup
- 1 x Wear plate
- 1 x Water-pump gasket
- 1 x Additional water-pump gasket
- 1 x Wear-plate-to-base gasket
- 1 x Water seal
- 4 x Mounting bolts
Important: The water-pump housing is not included.
Installation Notes
- Disconnect the battery and remove the engine cowling.
- Drain the lower-unit gear lubricant according to the applicable service procedure.
- Remove the lower unit from the driveshaft housing.
- Remove the water-pump cover and note the orientation of the impeller, key, cup, plate, and gaskets.
- Remove the old impeller and related service components. Clean the mating surfaces and inspect the housing before reassembly.
- Install the supplied components in the correct order for your engine model.
- Lubricate the impeller with water, glycerin, silicone grease, or dish soap during installation. Do not use petroleum-based lubricants.
- Reassemble the water pump and tighten fasteners to the engine manufacturer's specifications.
- Reinstall the lower unit and restore the gear lubricant level.
- Run the engine in water or with an appropriate flushing arrangement and verify a steady tell-tale stream before normal operation.
Troubleshooting & FAQ
How do I know if this kit fits my engine?
Match the complete Yamaha engine model and year with the compatibility information above, then compare the original water-pump assembly and OEM reference. Horsepower alone is not sufficient to confirm fitment.
What are the signs of a failing water pump?
Typical symptoms include overheating at idle or low speed, a weak or missing tell-tale stream, or an impeller that is cracked, brittle, distorted, or melted.
Is the water-pump housing included?
No. This listing is for the without-housing service-kit configuration. Inspect the existing housing and replace it separately if it is worn, scored, or damaged.
What is the difference between the Yamaha references?
The listed Yamaha numbers are related water-pump repair-kit references used across different model and year applications. Because catalog records associate specific numbers with specific engine models, verify the exact model before ordering rather than relying on the number family alone.
Do I need special tools for installation?
Standard outboard-service tools are generally required, and a torque wrench is recommended for reassembly. Follow the service procedure for the specific engine model.
Is this an OEM part?
No. This is an aftermarket replacement kit intended to replace the listed Yamaha water-pump repair-kit references.
Safety & Important Information
- Verify the complete engine model, year, original part configuration, and package contents before ordering.
- Do not operate an outboard with an inadequate cooling-water supply.
- Inspect the water-pump housing and related surfaces before installing the new components.
- Professional installation is recommended when the lower unit or water-pump assembly is unfamiliar.
About Sea Sierra
- Marine Parts Focus — Replacement components selected for common outboard service applications.
- Compatibility Guidance — Product information is organized around engine model, year, stroke, horsepower, and part-number conditions.
- Aftermarket Value — Practical replacement options for maintaining marine cooling systems.
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