Muffler Gasket – Fits Yamaha 25-55HP 2-Stroke & 40-50HP 4-Stroke (Replaces 663-45123-00-00)
Muffler Gasket – Fits Yamaha 25-55HP 2-Stroke & 40-50HP 4-Stroke (Replaces 663-45123-00-00) is backordered and will ship as soon as it is back in stock.
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Worry-free returns
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.).
You should expect to receive your refund within four weeks of giving your package to the return shipper, however, in many cases you will receive a refund more quickly. This time period includes the transit time for us to receive your return from the shipper (5 to 10 business days), the time it takes us to process your return once we receive it (3 to 5 business days), and the time it takes your bank to process our refund request (5 to 10 business days).
If you need to return an item, simply login to your account, view the order using the "Complete Orders" link under the My Account menu and click the Return Item(s) button. We'll notify you via e-mail of your refund once we've received and processed the returned item.
Delivery and Shipping
Delivery and Shipping
Free standard shipping on all orders under 1 KG
Muffler Gasket – Fits Yamaha 25-55HP 2-Stroke & 40-50HP 4-Strok...
Product Details
This aftermarket Muffler Gasket – Fits Yamaha 25-55HP 2-Stroke & 40-50HP 4-Stroke (Replaces 663-45123-00-00) provides a reliable seal for the exhaust system on a range of outboard engines. It is designed for Yamaha 2-Stroke models from 25–55 HP (1984–2009), 4-Stroke F-series engines from 40–50 HP (1999–2011), and select Mercury/Mariner 2-cylinder 2-stroke outboards from 48–60 HP.
This part directly replaces Yamaha OEM part numbers 663-45123-00-00 and 663-45123-00, as well as Mercury 27-81440M, Sierra 18-99009, and GLM 38032.
- Ensures a direct-fit installation with no modifications required.
- Made from an engineered composite/rubber compound for durability and a proper seal.
- Meets or exceeds the specifications of the original equipment version.
Part Number Matrix
Use this matrix to confirm equivalent references across OEM and aftermarket.
| Brand | Part Number |
|---|---|
| Yamaha | 663-45123-00-00 |
| Yamaha | 663-45123-00 |
| Mercury | 27-81440M |
| Sierra | 18-99009 |
| GLM | 38032 |
Engine & Model Compatibility
Confirm your engine model/year in the table below.
This gasket fits various Yamaha 2-stroke and 4-stroke outboards. Please verify your specific model is listed.
This gasket also fits certain 2-cylinder Mercury and Mariner outboards. Confirm your OEM part number is 27-81440M.
| Brand | Model | Rated HP | Stroke | Years | OEM Part No. | Notes |
|---|---|---|---|---|---|---|
| Yamaha | 25QEO | 25 | 2-Stroke | 663-45123-00-00 | ||
| Yamaha | 40H/N | 40 | 2-Stroke | 663-45123-00-00 | ||
| Yamaha | F40 | 40 | 4-Stroke | 663-45123-00-00 | ||
| Yamaha | F45 | 45 | 4-Stroke | 663-45123-00-00 | ||
| Yamaha | F50 | 50 | 4-Stroke | 663-45123-00-00 | ||
| Yamaha | 50ETN | 50 | 2-Stroke | 663-45123-00-00 | ||
| Yamaha | T50 | 50 | 2-Stroke | 663-45123-00-00 | ||
| Yamaha | 55B | 55 | 2-Stroke | 663-45123-00-00 | ||
| Yamaha | E55CM | 55 | 2-Stroke | 663-45123-00-00 | ||
| Mercury | 48 | 48 | 2-Stroke | 27-81440M | ||
| Mercury | 55 | 55 | 2-Stroke | 27-81440M | ||
| Mercury | W-48 | 48 | 2-Stroke | 27-81440M | ||
| Mercury | W-55 | 55 | 2-Stroke | 27-81440M | ||
| Mercury | 60 (2 cyl) | 60 | 2-Stroke | 27-81440M | 2-cylinder models only |
Technical Specs
- Product Type
- Muffler Gasket
- Installation
- Direct fit
- Material
- Engineered composite/rubber compound
- Dimensions
- 1.0" H x 4.0" W x 4.0" L
- Weight
- Approx. 0.06 lb (0.027 kg)
- Warranty
- 30-day return policy (retailer dependent)
- Country of Origin
- Original equipment version manufactured in Japan; aftermarket version meets equivalent standards.
What’s in the Box
- 1 x Gasket, Muffler (Replaces 663-45123-00-00)
Installation Notes
- Ensure the engine is off and cool to the touch. Disconnect the battery for safety.
- Locate the muffler cover or relevant exhaust component. You may need to remove other parts for access.
- Carefully unbolt and remove the component to expose the old gasket.
- Remove the old gasket entirely and discard it.
- Thoroughly clean both mating surfaces. Ensure they are free of old material, carbon, and corrosion for a proper seal.
- Position the new gasket correctly, aligning it with the bolt holes. Do not use sealant unless specified by your service manual.
- Reinstall the cover plate, tightening bolts to the manufacturer's recommended torque in a crisscross pattern.
- Reconnect the battery, start the engine, and check for any exhaust leaks around the newly sealed area.
Troubleshooting & FAQ
How do I know if my muffler gasket needs replacing?
Common signs of a failed gasket include a hissing or popping sound from the engine cowling, visible soot or black streaks around the exhaust joint, a noticeable exhaust smell, or a loss of engine performance.
Can I reuse my old muffler gasket?
No. Muffler gaskets are designed for single use. They compress and deform to create a seal and will not seal properly if re-installed.
Do I need to apply any sealant to this gasket?
This gasket is typically designed for a dry installation. Applying sealant can sometimes interfere with a proper seal. Always consult your engine's service manual for model-specific recommendations.
What happens if I don't replace a leaking muffler gasket?
A leaking gasket can lead to poor engine performance, increased fuel consumption, and potential damage to surrounding components from hot exhaust gases. It can also allow water to enter the engine, leading to severe internal damage.
The part number in my manual is 663-45123-00. Will this work?
Yes, this part is a direct replacement for 663-45123-00. The extra digits (-00-00) often signify packaging or minor revisions that do not affect the part's fit or function.
Will this fit a Mercury 60 HP 4-cylinder engine?
No. This gasket is specified to fit 2-cylinder Mercury 60 HP models only. Always verify part compatibility by the OEM part number, not just by horsepower.
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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