Lower Unit Seal Kit – Fits Honda BF75/BF90 Outboard Motors (Replaces 18-8366, 91251-ZW1-003, 91252-ZW1-003, 91253-ZW1-003, 91254-ZW1-003, 91255-ZW1-003)
Lower Unit Seal Kit – Fits Honda BF75/BF90 Outboard Motors (Replaces 18-8366, 91251-ZW1-003, 91252-ZW1-003, 91253-ZW1-003, 91254-ZW1-003, 91255-ZW1-003) is backordered and will ship as soon as it is back in stock.
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Delivery and Shipping
Delivery and Shipping
Orders are typically processed within 1–2 business days.
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Lower Unit Seal Kit – Fits Honda BF75/BF90 Outboard Motors (Replace...
Lower Unit Seal Kit – Fits Honda BF75/BF90 Outboard Motors (Replaces 18-8366, 91251-ZW1-003, 91252-ZW1-003, 91253-ZW1-003, 91254-ZW1-003, 91255-ZW1-003) is backordered and will ship as soon as it is back in stock.
Product Details
This comprehensive Lower Unit Seal Kit – Fits Honda BF75/BF90 Outboard Motors is designed to restore the gearcase integrity of Honda 75-90 HP, 4-Stroke outboards from 1997-1998 and later models. It provides all the essential seals to prevent water intrusion and oil leaks, ensuring your lower unit runs smoothly and efficiently.
The kit serves as a direct replacement for Sierra Marine aftermarket part 18-8366 and several individual Honda OEM seals, including 91251-ZW1-003, 91252-ZW1-003, 91253-ZW1-003, 91254-ZW1-003, and 91255-ZW1-003, offering a complete solution for gearcase resealing.
- Engineered for direct OEM replacement fitting.
- Specifically made for the Honda BF75/BF90 gearcase.
- Includes all five critical lower unit seals for a full service.
Part Number Matrix
Use this matrix to confirm equivalent references across OEM and aftermarket.
| Brand | Part Number | Notes |
|---|---|---|
| Sierra | 18-8366 | Aftermarket Kit |
| Honda | 91251-ZW1-003 | Driveshaft Seal |
| Honda | 91252-ZW1-003 | Propeller Shaft Seal, Inner |
| Honda | 91253-ZW1-003 | Shift Shaft Seal |
| Honda | 91254-ZW1-003 | Driveshaft Oil Seal |
| Honda | 91255-ZW1-003 | Propeller Shaft Seal, Outer |
Engine & Model Compatibility
Confirm your engine model/year in the table below.
This kit is specifically designed for certain Honda outboard models. Please check your engine details carefully.
| Brand | Model | Rated HP | Stroke | Years | OEM Part No. | Notes |
|---|---|---|---|---|---|---|
| Honda | BF75 | 75 | 4-Stroke | 1997–1998+ | 18-8366 | Sierra Marine aftermarket replacement |
| Honda | BF90 | 90 | 4-Stroke | 1997–1998+ | 18-8366 | Sierra Marine aftermarket replacement |
Technical Specs
- Product Type
- Lower Unit Seal Kit
- Installation
- Direct replacement
- Fitting Type
- Direct OEM replacement
- Other Technical Attributes
- For Honda BF75/BF90 gearcase
What’s in the Box
- 1 x Driveshaft Seal (Replaces 91251-ZW1-003)
- 1 x Propeller Shaft Seal, Inner (Replaces 91252-ZW1-003)
- 1 x Shift Shaft Seal (Replaces 91253-ZW1-003)
- 1 x Driveshaft Oil Seal (Replaces 91254-ZW1-003)
- 1 x Propeller Shaft Seal, Outer (Replaces 91255-ZW1-003)
Installation Notes
- Position the outboard securely and drain the gearcase oil into a suitable container.
- Remove the lower unit (gearcase) from the outboard's driveshaft housing.
- Carefully remove the propeller shaft and driveshaft bearing carrier assemblies to access the old seals.
- Extract the old, worn seals from the gearcase housing and carriers, taking care not to scratch the metal surfaces.
- Thoroughly clean all seal seating areas, removing any old sealant, corrosion, or debris.
- Lubricate the new seals with a light coat of marine grease.
- Using a proper seal driver or correctly sized socket, press the new seals into place until they are fully seated.
- Reinstall the bearing carriers, propeller shaft, and driveshaft.
- Reattach the lower unit to the outboard, ensuring the driveshaft and water tube align correctly.
- Refill the gearcase with the manufacturer-recommended gear lube to the proper level.
- Check for leaks around the drain/fill screws and shafts before returning to service.
Troubleshooting & FAQ
How do I know if this seal kit fits my Honda outboard?
This kit is designed for Honda BF75 (75 HP) and BF90 (90 HP) 4-Stroke models from 1997-1998 and later. Please verify the part numbers (Sierra 18-8366 or OEM seal numbers like 91251-ZW1-003) listed in the compatibility tables against your service manual or existing parts.
What are the signs of a failing lower unit seal?
Common symptoms include a milky, grey, or creamy appearance in your gear lube, which indicates water contamination. You might also notice gear oil leaking from the propeller shaft or driveshaft area. A burning smell from the lower unit can also be a sign of oil loss and overheating.
Is this a complete kit for a standard lower unit reseal?
Yes, this kit includes the five primary seals for the driveshaft, shift shaft, and propeller shaft, which are the most common wear items needed for a standard gearcase reseal project.
How often should lower unit seals be replaced?
It's good practice to inspect your gear lube at every oil change. Seals should be replaced preventatively every few hundred hours or every few years, depending on usage (especially in saltwater). They must be replaced immediately if you find any signs of water intrusion or oil leakage.
Can I just replace the one seal that is leaking?
While possible, it is highly recommended to replace all seals in the kit at the same time. If one seal has failed due to age or wear, the others are likely near the end of their service life as well. Replacing them all at once saves you from having to disassemble the lower unit again in the near future.
What else should I have on hand for the installation?
Besides basic hand tools, you will need a new bottle of marine gear lube, potentially new drain/fill screw gaskets, a seal removal tool (or a flat-head screwdriver used with caution), and a seal installation tool or appropriately sized sockets to press in the new seals without damaging them.
OEM vs. Aftermarket?
This listing is an aftermarket replacement (not OEM). Built to OEM-level specifications with comparable materials. Manufactured in an ISO 9002 facility, batch-inspected for consistency.
Shipping speed & cost
We ship worldwide quickly—typical transit 5–15 days. Standard shipping is free; expedited options appear at checkout where available.
Warranty & returns
Covered by a 1-year warranty against manufacturing defects under normal use. If issues arise, contact support with your order details. Returns are accepted within our standard window (unused & in original condition). See our policy page or reach out for instructions.
Safety & Important Info
- Verify images/specifications vs your original part. If anything differs—even if your model appears compatible—do not purchase.
- This is an aftermarket replacement, not an OEM component.
- Professional installation is recommended for safety and performance.
About Sea Sierra
- Pro-Grade Standards — We supply marine parts engineered to OEM-level tolerances and tested for real-world conditions.
- Fast Global Fulfillment — Free standard delivery to most regions in 5–15 days.
- Manufacturer-Direct Value — Fair pricing without compromising on materials or QC.
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