Straight Screw Plug Kit – Fits Yamaha 40HP-300HP (Replaces 688-45341, 90340-08002, 90430-08020)

Product Details

This Straight Screw Plug Kit – Fits Yamaha 40HP-300HP is a complete lower unit drain and screw plug replacement package designed for most Yamaha outboard engines from 40HP to 300HP. Confirm fitment by matching your engine's part number, as not all models within this horsepower range use identical plug configurations.

This kit directly replaces OEM part numbers 688-45341, 90340-08002, and 90430-08020, along with superseded references including 688-45341-10-00, 90340-08002-00, 90430-08003.

• Includes drain plug, straight screw plug, and two oil drain gaskets for a complete service
• Essential for routine lower unit maintenance and oil changes
• Always buy by part number to ensure correct fitment

Part Number Matrix

Use this matrix to confirm equivalent references across OEM and aftermarket.

Engine & Model Compatibility

Confirm your engine model/year in the table below.

Technical Specs

Application

Lower unit drain and screw plug service

Fitment Range

Yamaha 40HP–300HP (verify by part number)

Includes Gaskets

Yes, 2× oil drain gaskets (90430-08020)

Material

Corrosion-resistant metal and elastomer seals

What's in the Box

• 1× Lower Unit Drain Plug (688-45341)
• 1× Straight Screw Plug (90340-08002)
• 2× Lower Unit Oil Drain Gasket (90430-08020)

Installation Notes

1. Position the outboard vertically and allow the lower unit to cool completely.
2. Place a catch pan beneath the drain plug to collect used gear oil.
3. Remove the old drain plug and straight screw plug using the appropriate socket or wrench.
4. Inspect threads in the lower unit housing for damage or debris; clean if necessary.
5. Install new gaskets onto the drain plug and screw plug; ensure they seat evenly.
6. Thread each plug by hand first to avoid cross-threading, then snug to the manufacturer's torque specification.
7. Refill the lower unit with the correct grade and volume of gear oil per your service manual.
8. Run the engine briefly, then re-check for leaks around both plugs.

Troubleshooting & FAQ

How do I confirm this kit fits my Yamaha outboard?

Cross-reference the part numbers on your current drain plug and screw plug against 688-45341, 90340-08002, or 90430-08020. Do not rely solely on horsepower rating, as some models within the 40–300HP range may use different configurations.

Can I reuse the old gaskets?

No. Always replace drain gaskets during every oil change to ensure a proper seal and prevent leaks. This kit includes two new gaskets for that purpose.

What torque setting should I use for the drain plugs?

Consult your Yamaha service manual for the exact torque specification. Over-tightening can strip threads or crack the housing; under-tightening risks leaks.

Why are there two gaskets in the kit?

One gasket is for the lower unit drain plug (688-45341) and one for the straight screw plug (90340-08002), ensuring complete sealing at both drain points.

How often should I replace these plugs and gaskets?

Replace gaskets at every lower unit oil change—typically every 100 hours or annually. Inspect plugs for thread wear or corrosion and replace if damaged.

What are signs that my drain plugs need replacement?

Visible oil seepage around the plugs, stripped or rounded hex heads, corroded threads, or difficulty achieving proper torque all indicate it's time for new hardware.

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 against 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.