Water Pocket Gasket – Fits MerCruiser Alpha One Sterndrive (Replaces 27-558101)

$2.65

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Product Details

This Water Pocket Gasket is designed for Mercury MerCruiser R, MR, and Alpha One sterndrives and transom assemblies manufactured between 1983 and 1990. It provides a crucial seal between the water pocket cover and the drive shaft housing to prevent leaks and ensure proper cooling system function.

It serves as a direct replacement for Mercury/Quicksilver part number 27-558101, Mercury 27-55810, and Sierra 18-0894.

Installs between the water pocket cover and the drive shaft housing.
Made from a durable paper/fiber composite to ensure a reliable, long-lasting seal.
Essential for maintaining the integrity of the sterndrive's water cooling pathways.

Part Number Matrix

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

Brand	Part Number	Notes
Mercury / Quicksilver	27-558101	Current OEM Part Number
Mercury	27-55810	Superseded by 27-558101
Sierra	18-0894	Aftermarket Cross-Reference

Engine & Model Compatibility

Confirm your engine model/year in the table below.

This part is verified to fit the following Mercury MerCruiser models:

Brand	Model	Rated HP	Stroke	Years	OEM Part No.	Notes
MerCruiser	R/MR/Alpha One Sterndrive	Various	4-Stroke	1983–1990	27-558101	Serial #6225577 through 0F386995
MerCruiser	R/MR/Alpha One Transom Assembly	Various	4-Stroke	1983–1990	27-558101	Serial #6216687 through 0F386995
MerCruiser	165 Sterndrive	165	4-Stroke	1970–1977	27-558101	Used with water pocket cover assembly
MerCruiser	470 Sterndrive	Various	4-Stroke	1976–1977	27-558101	Used with water pocket cover assembly

Technical Specs

Product Type: Gasket
Application: Water pocket cover
Installation Location: Between water pocket cover and drive shaft housing
Material: Paper/Fiber
Dimensions: 4.0" H x 5.13" W x 1.06" L
Function: Used to seal water pocket cover to drive shaft housing

What’s in the Box

1 x Water Pocket Gasket (27-558101)

Installation Notes

Ensure the engine is off and cool, and disconnect the battery for safety.
Locate and unbolt the water pocket cover from the sterndrive's drive shaft housing.
Carefully remove the old gasket. Thoroughly clean both mating surfaces to remove any old gasket material, sealant, or corrosion.
Position the new gasket correctly on the drive shaft housing, aligning it with the bolt holes.
Reinstall the water pocket cover and tighten the bolts in a crisscross pattern to the manufacturer's specified torque. Do not overtighten.
After reassembly, reconnect the battery and check for leaks around the cover once the engine is running with a water supply.

Troubleshooting & FAQ

How do I know if this gasket will fit my MerCruiser engine?

Verify your engine model, year, and serial number against the compatibility table. This gasket is specifically for MerCruiser R, MR, Alpha One, 165, and 470 sterndrive models within the specified year and serial number ranges.

What are the signs of a failing water pocket gasket?

Symptoms of a bad gasket include visible water leaks around the water pocket cover (especially when the engine is running), engine overheating due to water pressure loss in the cooling system, and visible degradation or corrosion on the gasket itself during inspection.

Can I reuse the old gasket or use a sealant with this one?

No. Gaskets like this are designed for one-time use and should be replaced whenever the component is disassembled. Do not use sealants unless explicitly specified by the engine manufacturer, as it can interfere with proper seating and cause future leaks.

What is the purpose of the water pocket cover?

The water pocket cover is part of the sterndrive's cooling system. This gasket seals the cover to the drive shaft housing, maintaining the necessary water pressure and flow to cool the engine effectively.

When should this gasket be replaced?

This gasket should be replaced any time the water pocket cover is removed for service or inspection. It is also a critical part to replace if you are diagnosing and repairing an issue with engine overheating or water leaks in that area.

Is there a difference between part numbers 27-55810 and 27-558101?

Part number 27-55810 has been superseded by 27-558101, which is the current OEM part number. Both refer to the same part, and this aftermarket gasket is a direct replacement for both.

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

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