Lower Unit Oil Drain Plug Gasket – Fits Yamaha Outboard Motors (Replaces 90430-08003-00, 90430-08020-00)

Lower Unit Oil Drain Plug Gasket – Fits Yamaha Outboard Motors

This gasket provides a reliable seal for the lower unit drain and fill plugs on Yamaha outboard motors, preventing gear oil leaks. It is designed for a direct fit on all Yamaha 2-Stroke and 4-Stroke models from 1984 to the present.

This part directly replaces Yamaha 90430-08020-00, 90430-08003-00, 90430-08801-00, 604-45342-00-00; Mercury Marine 27-81987, 27-81987M; Sierra 18-4698, 18-46981-9; and Mallory Marine 9-60100.

• Material: Specialized oil and water-resistant fiber.
• Installation: Requires oil-coated threads and surfaces before installation.
• Compatibility: Fits all Yamaha 2-Stroke and 4-Stroke outboards (1984–Present).

Part Number Cross-Reference

Use this table to confirm equivalent part numbers across OEM and aftermarket brands.

Compatible Engine Models

Confirm your engine model/year in the table below. For Yamaha owners, here’s a guide to help you identify your engine’s serial/model: Yamaha Serial Number Guide. You can also review exploded diagrams to verify part numbers: Yamaha Parts Diagrams & Catalog.

Technical Specifications

Package Contents

• 1 x Lower Unit Drain Plug Gasket (90430-08003-00)
• Note: For complete gear oil changes, two gaskets are typically required—one for the lower drain plug and one for the upper fill plug.

Installation Guide

1. Position a suitable drain pan under the engine's lower unit.
2. Using a large flathead screwdriver or socket, carefully remove the lower drain plug screw.
3. Remove the upper vent plug screw to allow oil to drain completely.
4. Clean the magnetic tip of the drain plug to remove any metal shavings.
5. Remove and discard the old gasket from the drain plug.
6. Lightly coat the threads of the plug and the surfaces of the new gasket with fresh gear oil.
7. Install the new gasket onto the drain plug.
8. Fill the lower unit with the manufacturer-specified gear lubricant through the bottom hole until it flows out of the upper vent hole.
9. Reinstall the upper vent plug with its old gasket (or a new one). Tighten it securely.
10. Reinstall the lower drain plug with the new gasket.
11. Tighten both plugs to the specified torque: 7 ± 1 Nm (5.2 ± 0.7 lb-ft). Do not overtighten, as this can damage the gearcase.

Troubleshooting & FAQ

How do I confirm this fits my engine?

This gasket is designed for all Yamaha 2-stroke and 4-stroke outboard models from 1984 to the present. You can verify fitment by checking if your old gasket's part number is listed in our cross-reference table, such as 90430-08003-00 or the older 90430-08020-00.

My old gasket was reddish-orange, but this one is black. Is it the correct part?

Yes, this is correct. The black fiber gasket is the updated OEM-spec version that supersedes the earlier reddish-orange gaskets (like 90430-08020-00). It provides the same fit and improved sealing performance.

How often should I replace the drain plug gasket?

It is strongly recommended to replace the drain and fill plug gaskets every time you change your lower unit gear oil. Reusing old, compressed gaskets substantially increases the risk of a leak, which can lead to catastrophic gearcase failure from water intrusion.

What are the signs of a failing drain plug gasket?

The most common sign is a visible gear oil leak (a thick, pungent oil) around the drain or fill plug. Another critical sign is milky or cloudy gear oil, which indicates water has entered the gearcase, often due to a failed seal.

OEM vs. Aftermarket?

This listing is an aftermarket replacement part (not an OEM component). We build to OEM specifications using comparable-grade materials. Production is done in an ISO9002-certified facility, and each batch is inspected for consistent performance.

How fast do you ship and how much does it cost?

We offer fast global shipping—typically 5–15 days worldwide—and standard shipping is free. Expedited options are available at checkout depending on your location.

What is your warranty and return policy?

This product includes a 1-year warranty against manufacturing defects under normal use. If something goes wrong, contact our support team with your order details. Returns are accepted within our standard return window (unused & in original condition); please see our policy page or reach out for instructions.

Important Notes

• Verify that the product images and specifications match your original part. If discrepancies exist—even if your model is listed—do not proceed with the purchase.
• This product is an aftermarket replacement part and is not an OEM component.
• Professional installation is recommended to ensure safety and optimal performance.

Why Choose JLM MARINE?

• Quality Assured: As a trusted manufacturer for over 20 years, we supply top marine brands globally.
• Fast Global Shipping: Free delivery worldwide in 5–15 days.
• Direct from Manufacturer: Competitive pricing without compromising quality.