Impeller Repair Kit for Yamaha 40/50 HP 2-Stroke Outboards – Replaces Yamaha 63D-W0078-01-00, Sierra 18-3434
Impeller Repair Kit for Yamaha 40/50 HP 2-Stroke Outboards – Replaces Yamaha 63D-W0078-01-00, Sierra 18-3434 is backordered and will ship as soon as it is back in stock.
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Impeller Repair Kit for Yamaha 40/50 HP 2-Stroke Outboards – Replac...
Impeller Repair Kit for Yamaha 40/50 HP 2-Stroke Outboards – Replaces Yamaha 63D-W0078-01-00, Sierra 18-3434 is backordered and will ship as soon as it is back in stock.
Product Details
This aftermarket impeller repair kit is designed for selected Yamaha 40 HP and 50 HP 2-stroke outboards. It replaces Yamaha water-pump reference 63D-W0078-01-00 and corresponds to Sierra part number 18-3434.
The kit is intended to renew the key wear components of the water-pump assembly, including the impeller, wear plate, insert cup, gasket, key, seals, O-ring, bolts, washers, and pump-housing cover. It is the version supplied without the complete water-pump housing; confirm the housing condition before installation.
- Helps restore water-pump circulation and cooling-system performance.
- Includes the impeller, gaskets, wear plate, insert cup, key, seals, O-ring, fasteners, and cover listed below.
- Designed as an aftermarket replacement for the specified Yamaha application.
- Verify the exact model designation and production year before ordering.
Part Number Matrix
These are the customer-facing manufacturer and aftermarket references associated with this repair-kit application.
| Brand | Part Number | Role |
|---|---|---|
| Yamaha | 63D-W0078-01-00 | OEM reference |
| Yamaha | 63D-44311-00-00 | Related water-pump housing reference; housing is not included in this version |
| Sierra | 18-3434 | Aftermarket repair-kit reference |
Engine & Model Compatibility
The available catalog application data identifies this repair-kit application for the following Yamaha outboards. Model suffixes, year ranges, and cylinder configuration must remain matched when checking fitment.
| Brand | Model or Series | Rated HP | Stroke | Year or Range | Notes |
|---|---|---|---|---|---|
| Yamaha | 40 / 50 | 40–50 | 2-Stroke | 1995–2003 | Catalog range; confirm the exact model suffix |
| Yamaha | P40 | 40 | 2-Stroke | 1998 | Specific catalog application |
| Yamaha | C40, 3-cylinder | 40 | 2-Stroke | 1997–2002 | Confirm 3-cylinder configuration |
| Yamaha | C50 | 50 | 2-Stroke | 1999–2001 | Confirm the exact model suffix |
| Yamaha | F40 2.6L | 40 | 4-Stroke | 1999 | Catalog-listed application; verify the 2.6L model designation before purchase |
| Yamaha | F50 | 50 | 4-Stroke | 1995–2003 | Catalog-listed application; confirm the exact model and year |
| Yamaha | P50 | 50 | 2-Stroke | 1995–1996 | Specific catalog application |
| Yamaha | F60 | 60 | 4-Stroke | 2002–2003 | Catalog-listed application; verify the exact model suffix |
Important: The application information above is not a blanket fitment claim for every Yamaha 40–60 HP engine. Yamaha model families can use different water-pump components. Compare the original parts and consult the engine service information when the model, year, cylinder configuration, or displacement differs.
Technical Specifications
- Product Type
- Impeller repair kit
- Application
- Water-pump cooling-system service
- Housing Included
- No complete water-pump housing; a pump-housing cover is included as listed
- Installation
- Replacement service part; installation should follow the applicable Yamaha service procedure
- Primary OEM Reference
- Yamaha 63D-W0078-01-00
- Aftermarket Reference
- Sierra 18-3434
What's in the Box
- 1 x Water-pump case gasket — Yamaha 63D-44316-00-00
- 1 x Impeller — Yamaha 697-44352-00-00
- 1 x Wear plate — Yamaha 63D-44323-00-00
- 1 x Impeller key — Yamaha 90280-03M03-00
- 1 x Insert cup — Yamaha 63D-44322-00-00
- 1 x Bolt set of 4 — Yamaha 90119-08M15-00
- 1 x Water-pump housing cover — Yamaha 63D-44312-00-00
- 4 x Bolt washers — Yamaha 90209-08M02-00
- 1 x O-ring — Yamaha 93210-59MG7-00
- 1 x Water seal — Yamaha 663-44366-00-00
Not included: the complete water-pump housing. Reuse is appropriate only if the existing housing is serviceable and undamaged.
Installation Notes
- Turn the engine off, allow it to cool, and follow all applicable marine-service safety procedures.
- Remove the lower unit according to the engine service manual.
- Remove the existing water-pump cover and disassemble the pump in order, recording the position of each component.
- Inspect the existing housing, driveshaft keyway, water tube, and mounting surfaces for scoring, corrosion, blockage, or other damage.
- Clean the mating surfaces and install the new gasket, wear plate, insert cup, impeller key, and impeller.
- Install the impeller with the vanes oriented for the direction of shaft rotation specified by the service procedure.
- Fit the O-ring, water seal, cover, washers, and fasteners. Tighten fasteners to the manufacturer's specified torque.
- Reinstall the lower unit, ensuring that the driveshaft and water tube engage correctly.
- Run the engine using the appropriate water supply and confirm cooling-water flow and normal operating temperature before returning the boat to service.
Maintenance & Troubleshooting
What symptoms can indicate a worn water-pump impeller?
Overheating, a weak or intermittent tell-tale stream, reduced cooling-water flow, or damaged and missing impeller vanes can indicate that the water pump requires service. A blocked water passage or damaged housing can produce similar symptoms and should also be checked.
Does this kit include the complete water-pump housing?
No. This repair-kit configuration is supplied without the complete water-pump housing. It includes the water-pump housing cover and the other components listed in the package contents. Inspect the existing housing before installation.
Will this fit every Yamaha 40–60 HP outboard?
No. The application is limited to the Yamaha model, stroke, cylinder, displacement, and year combinations listed above. Do not rely on horsepower alone; compare the original part number and exact engine model designation.
Is this an OEM Yamaha part?
No. This listing is for an aftermarket replacement kit. Yamaha part numbers are shown only as OEM reference numbers for identification and fitment checking.
When should the impeller be replaced?
Replace the impeller when inspection shows hardened, cracked, distorted, or missing vanes, or when cooling-water flow is reduced. Follow the maintenance interval and inspection guidance for the specific engine.
Safety & Important Information
- Verify the exact Yamaha model, year, stroke, cylinder configuration, and OEM reference before ordering.
- Do not install a damaged, scored, or corroded water-pump housing with new internal components.
- Use the applicable service manual for removal, installation, fastener torque, and testing procedures.
- Professional installation is recommended if you are not familiar with outboard lower-unit or water-pump service.
- This is an aftermarket replacement kit, not an OEM Yamaha component.
About Sea Sierra
- Marine Replacement Parts — Parts selected for common outboard maintenance and repair applications.
- Application-Focused Listings — Customer-facing references and fitment details are provided to support part-number verification.
- Service-Ready Components — Replace worn water-pump service parts and inspect related components before returning the engine to operation.
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