Powerhead Base Gasket – Fits Mercury/Mariner 6-15 HP Outboards (Replaces 27-191861)

$7.65 $12.00

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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Mercury	19186	Superseded/Previous Part Number
Mercury	423701	Superseded/Previous Part Number
Mercury	423702	Superseded/Previous Part Number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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