Powerhead Base Gasket – Fits Mercury/Mariner 6-15 HP Outboards (Replaces 27-191861)
Powerhead Base Gasket – Fits Mercury/Mariner 6-15 HP Outboards (Replaces 27-191861) 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
Powerhead Base Gasket – Fits Mercury/Mariner 6-15 HP Outboards (Rep...
Product Details
This replacement Powerhead Base Gasket provides a precision seal between the lower crankcase and the cylinder block. It is designed for a wide range of Mercury and Mariner 6-15 HP, 2-stroke outboards manufactured between 1986 and 2006, including Magnum, Marathon, Sea Pro, and Viking series.
It is a direct replacement for Mercury OEM part 27-191861 and also interchanges with previous part numbers 19186, 423701, and 423702.
- Installs between the lower crankcase and cylinder block to prevent leaks.
- Engineered to meet OEM specifications for dimensional accuracy and fit.
- Compatible with numerous engine serial numbers across multiple model years.
Part Number Matrix
Use this matrix to confirm equivalent references across OEM and aftermarket.
| Brand | Part Number | Notes |
|---|---|---|
| Mercury | 27-191861 | Current OEM Part Number |
| Mercury | 19186 | Superseded/Previous Part Number |
| Mercury | 423701 | Superseded/Previous Part Number |
| Mercury | 423702 | Superseded/Previous Part Number |
Engine & Model Compatibility
Confirm your engine model/year in the table below.
This gasket fits a broad range of 2-stroke outboards under the Mercury and Mariner brands from the mid-1980s through the mid-2000s.
| Brand | Model | Rated HP | Stroke | Years | OEM Part No. | Notes |
|---|---|---|---|---|---|---|
| Mercury | 6 | 6 | 2-Stroke | 1986–2006 | 27-191861 | Multiple serial number ranges |
| Mercury | 8 | 8 | 2-Stroke | 1986–2006 | 27-191861 | Multiple serial number ranges |
| Mercury | 9.9 | 9.9 | 2-Stroke | 1986–2006 | 27-191861 | Multiple serial number ranges |
| Mercury | 10 MAGNUM | 10 | 2-Stroke | 1986–1998 | 27-191861 | Various serial ranges |
| Mercury | 10 MARATHON | 10 | 2-Stroke | 1986–2006 | 27-191861 | Multiple serial ranges |
| Mercury | 10 SEA PRO | 10 | 2-Stroke | 1986–2006 | 27-191861 | Multiple serial ranges |
| Mercury | 10 VIKING | 10 | 2-Stroke | 1990–2006 | 27-191861 | Belgium production models |
| Mercury | 15 | 15 | 2-Stroke | 1986–2006 | 27-191861 | Multiple serial ranges |
| Mercury | 15 MARATHON | 15 | 2-Stroke | 1992–2006 | 27-191861 | Multiple serial ranges |
| Mercury | 15 SEA PRO | 15 | 2-Stroke | 1992–2006 | 27-191861 | Multiple serial ranges |
| Mercury | 15 VIKING | 15 | 2-Stroke | 1995–2006 | 27-191861 | Belgium production models |
| Mercury | XR10 | 10 | 2-Stroke | 1986–1998 | 27-191861 | Special performance model |
Technical Specs
- Product Type
- Powerhead Base Gasket
- Installation Location
- Between lower crankcase and cylinder block
- Dimensions
- 25.5 cm × 14.5 cm × 0.1 cm
- Weight
- Approx. 34 g (1.2 oz)
- OEM Number
- 27-191861
- Previous Part Numbers
- 19186, 423701, 423702
What’s in the Box
- 1 x Powerhead Base Gasket (27-191861)
Installation Notes
- Disconnect the battery and spark plug wires to prevent accidental starting.
- Drain the engine oil and coolant completely.
- Carefully disconnect all fuel lines, electrical connections, and linkages attached to the powerhead.
- Unbolt and remove the powerhead from the midsection. This may require a hoist for heavier engines.
- Remove the old powerhead base gasket and thoroughly clean both mating surfaces of any residue.
- Position the new gasket correctly, ensuring all bolt holes line up perfectly.
- Reinstall the powerhead, torquing the bolts to the manufacturer's specified sequence and values.
- Reconnect all linkages, fuel lines, and electrical systems.
- Refill the engine with fresh oil and coolant.
- Start the engine and carefully check for any fuel, oil, or exhaust leaks around the gasket seal.
Troubleshooting & FAQ
What are the signs of a failed powerhead base gasket?
Common symptoms include external oil or water leaks between the cylinder block and crankcase, loss of crankcase compression, or evidence of water in the cylinders. An engine that runs rough or has low power can also indicate a leak.
Can I reuse my old gasket if it looks okay?
No. Gaskets are single-use components designed to crush and seal upon installation. Once the powerhead is removed, the old gasket will not provide a reliable seal and must be replaced to prevent leaks.
Does this gasket require any sealant during installation?
Generally, modern gaskets like this are designed to be installed dry. However, always consult your engine's specific service manual. Some manuals may recommend a light application of a specific sealant, especially on older engines or surfaces with minor imperfections.
How can I be sure this fits my engine if the serial number ranges are confusing?
The best method is to match the OEM part number (27-191861) from your engine's official parts diagram. If you cannot find this, visually compare your old gasket to the product images, paying close attention to the shape and bolt hole pattern.
What’s the difference between OEM and this aftermarket part?
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.
How fast is shipping and what does it cost?
We ship worldwide quickly—typical transit 5–15 days. Standard shipping is free; expedited options appear at checkout where available.
What is the warranty and return policy?
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.
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