Yamaha 4-Stroke Outboard Lower Unit Drain Gasket – Replaces Yamaha 90430-08003-00, 90430-08020-00 and Mercury 27-81987
Yamaha 4-Stroke Outboard Lower Unit Drain Gasket – Replaces Yamaha 90430-08003-00, 90430-08020-00 and Mercury 27-81987 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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Yamaha 4-Stroke Outboard Lower Unit Drain Gasket – Replaces Yamaha ...
Yamaha 4-Stroke Outboard Lower Unit Drain Gasket – Replaces Yamaha 90430-08003-00, 90430-08020-00 and Mercury 27-81987 is backordered and will ship as soon as it is back in stock.
Product Details
This fiber/composite Yamaha Outboard Lower Unit Drain Gasket creates a secure, leak-resistant seal for the lower-unit drain and vent plugs. It is intended for a wide range of Yamaha 4-stroke outboard motors from 2.5 HP through 350 HP, depending on the specific model, year and application.
This replacement gasket corresponds to Yamaha part numbers 90430-08003-00 and 90430-08020-00, with aftermarket cross-references including Sierra 18-0826 and Mercury 27-81987.
- Installs with basic hand tools.
- Functions as a compression-style crush washer for the plug sealing surface.
- Black composite style associated with the later replacement part.
- Use a new gasket whenever the lower-unit drain or vent plug is removed.
Part Number Matrix
Use the references below to compare OEM and aftermarket numbers. Confirm the plug and gasket dimensions against the original part before installation.
| Brand | Part Number | Notes |
|---|---|---|
| Yamaha | 90430-08003-00 | Current replacement reference listed for the gasket. |
| Yamaha | 90430-08020-00 | Earlier reference associated with the previous gasket style. |
| Sierra | 18-0826 | Aftermarket cross-reference. |
| Mercury | 27-81987 | Aftermarket/interchange reference. |
Engine & Model Compatibility
The gasket is listed for the following Yamaha 4-stroke outboard model families. Model-year, serial-number and application conditions can vary, so compare the original gasket and plug before ordering.
| Brand | Model | Rated HP | Stroke | Listed Years | OEM Reference |
|---|---|---|---|---|---|
| Yamaha | F2.5 | 2.5 | 4-Stroke | 2003–Present | 90430-08003-00 |
| Yamaha | F4 | 4 | 4-Stroke | 1999–Present | 90430-08003-00 |
| Yamaha | F6 | 6 | 4-Stroke | 1999–Present | 90430-08003-00 |
| Yamaha | F8 | 8 | 4-Stroke | 2000–Present | 90430-08003-00 |
| Yamaha | F9.9 | 9.9 | 4-Stroke | 2000–Present | 90430-08003-00 |
| Yamaha | F15 | 15 | 4-Stroke | 1998–Present | 90430-08003-00 |
| Yamaha | F20 | 20 | 4-Stroke | 1998–Present | 90430-08003-00 |
| Yamaha | F25 | 25 | 4-Stroke | 1998–Present | 90430-08003-00 |
| Yamaha | F30 | 30 | 4-Stroke | 1998–Present | 90430-08003-00 |
| Yamaha | F40 | 40 | 4-Stroke | 1999–Present | 90430-08003-00 |
| Yamaha | F50 | 50 | 4-Stroke | 1999–Present | 90430-08003-00 |
| Yamaha | F60 | 60 | 4-Stroke | 2002–Present | 90430-08003-00 |
| Yamaha | F70 | 70 | 4-Stroke | 2010–Present | 90430-08003-00 |
| Yamaha | F75 | 75 | 4-Stroke | 1998–Present | 90430-08003-00 |
| Yamaha | F80 | 80 | 4-Stroke | 2000–Present | 90430-08003-00 |
| Yamaha | F90 | 90 | 4-Stroke | 2000–Present | 90430-08003-00 |
| Yamaha | F100 | 100 | 4-Stroke | 2000–Present | 90430-08003-00 |
| Yamaha | F115 | 115 | 4-Stroke | 2000–Present | 90430-08003-00 |
| Yamaha | F150 | 150 | 4-Stroke | 2004–Present | 90430-08003-00 |
| Yamaha | F175 | 175 | 4-Stroke | 2004–Present | 90430-08003-00 |
| Yamaha | F200 | 200 | 4-Stroke | 2004–Present | 90430-08003-00 |
| Yamaha | F225 | 225 | 4-Stroke | 2004–Present | 90430-08003-00 |
| Yamaha | F250 | 250 | 4-Stroke | 2004–Present | 90430-08003-00 |
| Yamaha | F300 | 300 | 4-Stroke | 2004–Present | 90430-08003-00 |
| Yamaha | F350 | 350 | 4-Stroke | 2008–Present | 90430-08003-00 |
Technical Specifications
- Product Type
- Lower-unit drain and vent plug gasket
- Installation
- Manual installation with basic hand tools
- Sealing Method
- Compression/crush washer
- Material
- Fiber/composite
- Color
- Black replacement style; earlier versions may appear reddish-orange
- Outside Diameter
- Approximately 19 mm
- Approximate Weight
- Less than 5 g
- Thread Application
- Listed for compatible M8 drain-plug applications
What's in the Box
- 1 × Lower-unit drain/vent plug gasket
This gasket can be used on both the upper vent plug and lower drain plug where specified by the engine application. A complete lower-unit oil change commonly requires two gaskets.
Installation Notes
- Place a drain pan beneath the lower unit.
- Remove the lower drain plug and upper vent plug.
- Allow the gear oil to drain completely. Inspect the oil for a milky appearance or metal particles.
- Clean the plug and gearcase sealing surfaces.
- Remove and discard the old gaskets. Do not reuse crushed gaskets.
- Install a new gasket on each plug as required by the application.
- Fill the lower unit with the recommended gear lubricant through the lower drain opening until lubricant appears at the upper vent opening.
- Install the upper vent plug with its new gasket first.
- Remove the filler tube and install the lower drain plug promptly.
- Tighten both plugs to the manufacturer's specified torque. Do not overtighten.
- Wipe the area clean and check for leaks after servicing.
Troubleshooting & FAQ
How do I avoid overtightening the gasket?
Use a torque wrench and follow the engine manufacturer's specified torque. Excessive tightening can distort the gasket, damage the plug or damage the sealing surface.
The replacement gasket feels harder than my old gasket. Is that normal?
The listed replacement reference is associated with a black composite style, while earlier gasket versions may appear reddish-orange. Compare the dimensions and sealing surface with the original part before installation.
How often should the gasket be replaced?
Install a new gasket whenever the drain or vent plug is removed, especially during a lower-unit gear-oil change. Reusing a compressed gasket can contribute to leakage and water intrusion.
What are signs of a failed plug gasket?
Oil seepage or dripping around the drain or vent plug may indicate a sealing problem. Milky or creamy gear oil can indicate water intrusion and should be investigated before further operation.
Is this an OEM part?
This listing is for an aftermarket replacement gasket corresponding to the part-number references shown above. It is not represented as a Yamaha- or Mercury-branded OEM component.
Shipping speed and cost
Standard shipping is free, with typical transit times of 5–15 days. Expedited options appear at checkout where available.
Warranty and returns
The product is covered by a 1-year warranty against manufacturing defects under normal use. Returns are accepted within the standard return window when the item is unused and in its original condition. Contact support for instructions.
Safety & Important Information
- Confirm the engine model, year, serial range and original gasket dimensions before ordering.
- Compare the replacement with the original part; do not install it if the sealing surface or dimensions differ.
- Use the manufacturer's specified gear lubricant and plug torque.
- This is an aftermarket replacement, not an OEM-branded component.
- Professional installation is recommended when the correct torque or service procedure is uncertain.
About Sea Sierra
- Pro-Grade Standards — Marine replacement parts selected for dependable service and consistent fit.
- Fast Global Fulfillment — Free standard delivery to most regions, with typical transit of 5–15 days.
- Manufacturer-Direct Value — Fair pricing with attention to material quality and production consistency.
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