Yamaha – Drain Plug Gasket – 90430-08003-00

The Yamaha Marine 90430-08003-00 Drain Plug Gasket is a genuine OEM sealing washer used on Yamaha outboard lower-unit gearcase drain and vent screws. It seals the gear-lube drain/fill plug and upper oil-level vent plug to help prevent water intrusion into the gearcase and gear oil leakage out of the lower unit. This is a small service part, but it is critical during every lower-unit gear oil change.

Key Features

• Yamaha part number: 90430-08003-00
• Product type: Lower-unit drain / vent plug gasket
• Application location: Gearcase oil drain/fill screw and upper vent screw
• Typical quantity per service: Two gaskets per gear oil change
• Material style: Black rubber/fiber composite sealing washer
• Approximate dimensions: 13 mm outside diameter x 8 mm inside diameter x 1.8 mm thick
• Service role: Helps seal the lower-unit gear oil cavity against water entry and oil leakage
• Common service use: 100-hour service, seasonal gear-lube change, lower-unit inspection, and drain screw resealing

Engine Compatibility

This gasket is used across many Yamaha 2-stroke and 4-stroke outboard lower units where the parts diagram calls for 90430-08003-00 or a confirmed superseded gasket number.

Common use includes Yamaha outboard gearcases that use separate lower drain/fill and upper vent screws. Fitment should be confirmed by outboard model, year, serial number, lower-unit type, and Yamaha parts diagram.

Fitment Notice

Most Yamaha lower-unit oil changes require two gaskets: one for the lower drain/fill screw and one for the upper vent screw. These are crush-style sealing parts and should be replaced every time the screws are removed.

Do not reuse old drain plug gaskets. A flattened, cracked, hardened, or over-compressed gasket may allow water to track into the gearcase, causing milky gear oil, bearing damage, corrosion, or lower-unit failure.

When This Part Needs Replacement

Replace this gasket during every lower-unit gear oil service, any time the drain or vent screw is removed, or whenever the gasket shows compression damage, cracking, splitting, swelling, hardening, or distortion.

This gasket should also be replaced if gear oil appears milky, water is found in the gearcase, oil leaks from either screw, or the lower unit is being inspected after impact, fishing-line damage, seal failure, or long storage.

Installation Notes

Drain and refill the lower unit following the Yamaha service procedure for the specific outboard model. Install a new gasket on both the drain/fill screw and the vent screw before final tightening. Lightly coat the screw threads and gasket faces with clean gear oil before installation.

Do not overtighten the screws. Excessive torque can crush or split the gasket and may damage the gearcase threads. Use the Yamaha service manual torque specification for the exact model. Where applicable, common service references list approximately 7 Nm / 5.2 lb-ft for this style of screw, but model-specific service data should always take priority.

Alternate/Superseded Part Numbers

• Current Yamaha part number: 90430-08003-00
• Superseded Yamaha reference: 90430-08020-00
• Superseded Yamaha reference: 90430-08801-00
• Superseded Yamaha reference: 604-45342-00-00
• Sierra Marine cross-reference: 18-4698
• Mercury / Quicksilver reference: 81987 / 27-81987

Cross-reference numbers should be confirmed against the outboard model, drain screw style, and gearcase parts diagram before substitution.

Parts Desk Insight

This gasket is inexpensive but important. For a proper Yamaha lower-unit gear oil service, replace both drain plug gaskets every time. Reusing old gaskets is one of the easiest ways to create a water path into the gearcase, especially after seasonal service or repeated drain screw removal.

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