Lower Unit Drain Gasket – Fits Yamaha Outboard Engines (Replaces 90430-08020-00)
Lower Unit Drain Gasket – Fits Yamaha Outboard Engines (Replaces 90430-08020-00) is backordered and will ship as soon as it is back in stock.
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Worry-free returns
You may return most new, unopened items within 7 days of delivery for a full refund. We'll also pay the return shipping costs if the return is a result of our error (you received an incorrect or defective item, etc.).
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Delivery and Shipping
Delivery and Shipping
Free standard shipping on all orders under 1 KG
Lower Unit Drain Gasket – Fits Yamaha Outboard Engines (Replaces 90...
Product Details
This Lower Unit Drain Gasket – Fits Yamaha Outboard Engines (Replaces 90430-08020-00) creates a secure seal for the gearcase oil drain plug on all Yamaha outboard models from 1984 to the present, including all horsepower ranges (2.5–350 HP) for both 2-stroke and 4-stroke engines. It is designed to prevent gear oil leaks and ensure proper lubrication system performance.
This part is a direct replacement for Yamaha OEM part numbers 90430-08020-00 and 90430-08003-00, as well as Sierra 18-0924 and GLM 87110.
- Engineered as a single-use replacement for a reliable seal every time.
- Constructed from copper to OEM factory specifications for durability.
- Universal design fits the entire range of Yamaha outboard engines.
Part Number Matrix
Use this matrix to confirm equivalent references across OEM and aftermarket.
| Brand | Part Number | Superseded By |
|---|---|---|
| Yamaha | 90430-08020-00 | 90430-08003-00 |
| Sierra | 18-0924 | |
| GLM | 87110 |
Engine & Model Compatibility
Confirm your engine model/year in the table below.
Yamaha designed this gasket to fit all outboard models with the common lower unit drain plug configuration. This is a universal part across their lineup.
| Brand | Model | Rated HP | Stroke | Years | OEM Part No. | Notes |
|---|---|---|---|---|---|---|
| Yamaha | All Outboard Models | 2.5-350 | 2-Stroke & 4-Stroke | 1984–Present | 90430-08020-00 | Superseded by 90430-08003-00 |
Technical Specs
- Product Type
- Gearcase Drain Plug Gasket
- Installation
- Replacement only (single-use item)
- Material
- Copper
- Dimensions
- Inner diameter: 8 mm
- Product Dimensions
- Height: 2.0; Width: 8.0; Length: 9.0;
- Box Dimensions
- Height: 2.0; Width: 8.0; Length: 9.0;
- Other Technical Attributes
- OEM factory original design
What’s in the Box
- 1 x Gasket (Replaces 90430-08020-00/90430-08003-00)
Installation Notes
- Position a suitable oil drain pan under the lower unit of your engine.
- Carefully remove the lower unit oil drain plug screw.
- Allow the gear oil to drain completely. Inspect the oil for any signs of water intrusion or metal shavings.
- Remove and discard the old drain plug gasket from the screw. Never reuse an old gasket.
- Thoroughly clean the drain plug screw and the sealing surface on the gearcase.
- Place the new gasket onto the drain plug screw.
- Reinstall the screw and tighten it to the manufacturer's specified torque. Do not overtighten, as this can damage the gearcase.
- Refill the lower unit with the correct type and amount of new gear oil through the upper fill hole.
- Install the upper vent plug with its gasket, and check both plugs for leaks.
Troubleshooting & FAQ
Will this gasket fit my specific Yamaha engine?
Yes, this gasket is a universal part designed to fit all Yamaha 2-stroke and 4-stroke outboard engines from 1984 to present, across all horsepower ratings (2.5HP to 350HP).
Is this a single-use gasket?
Yes, this is a crush washer designed for one-time use. To ensure a proper, leak-free seal, it should be replaced every time you change your lower unit gear oil.
How often should I replace this gasket?
You should replace the drain plug gasket with every gear oil change. Most manufacturers recommend changing the lower unit oil at least once a year or every 100 hours of operation, whichever comes first.
What are the signs of a failing drain plug gasket?
The most common sign of a failing gasket is a slow drip or leak of gear oil from the lower unit drain plug. You may notice an oily sheen on the water below your engine or oil residue on the skeg. A leaking gasket can lead to low oil levels and eventually catastrophic gearcase failure.
What is the difference between part number 90430-08020-00 and 90430-08003-00?
Part number 90430-08020-00 was superseded by 90430-08003-00. They are functionally identical and completely interchangeable. This product replaces both OEM part numbers.
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.
Payment & Security
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