Piston Kit – Fits Mercury/Mariner 2-Stroke 3-Cylinder 40-50 HP (Replaces 779-96152)

$53.73 $85.00

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If you have any questions, feel free to email us at info@sierramarines.com, and we’ll get back to you within 20–36 hours.

Product Details

This aftermarket Piston Kit – Fits Mercury/Mariner 2-Stroke 3-Cylinder 40-50 HP is engineered for a range of Mercury/Mariner 40-50 HP, 2-Stroke, 3-Cylinder engines (1998–2006) and select Tohatsu 40-50 HP, 2-Stroke, 3-Cylinder models (2002–2005).

It provides a direct interchange for Mercury part number 779-96152 and Tohatsu part number 3C8-00004-0 for the standard bore size.

Manufactured from high-quality cast aluminum alloy for durability and performance.
Engineered for the standard 68mm (2.992") cylinder bore.
This complete kit includes the piston, rings, piston pin, and circlips for a full replacement.

Part Number Matrix

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

Brand	Part Number	Notes
Mercury	779-96152	Standard Bore Size
Tohatsu	3C8-00004-0	Standard Bore Size

Engine & Model Compatibility

Confirm your engine model/year in the table below.

For Mercury/Mariner engines, this kit fits 3-cylinder powerheads from 1998–2005 that utilize a 2.992" standard bore.

For Tohatsu outboards, this kit is compatible with 3-cylinder M40D2, M50D2, NS40D2, and NS50D2 models from 2002–2005.

Brand	Model	Rated HP	Stroke	Years	OEM Part No.	Notes
Mercury	40 HP LIGHTNING/XR/MXL MARATHON	40	2-Stroke	1998–2005	779-96152	3-Cylinder, 2.992" STD Bore
Mercury	50 HP	50	2-Stroke	1998–2005	779-96152	3-Cylinder, 2.992" STD Bore
Mercury	60 HP	60	2-Stroke	1998–2005	779-96152	3-Cylinder powerheads that use 2.992" bore
Tohatsu	M40D2	40	2-Stroke	2002–2005	3C8-00004-0	3-Cylinder models
Tohatsu	M50D2	50	2-Stroke	2002–2005	3C8-00004-0	3-Cylinder models
Tohatsu	NS40D2	40	2-Stroke	2002–2005	3C8-00004-0	3-Cylinder models
Tohatsu	NS50D2	50	2-Stroke	2002–2005	3C8-00004-0	3-Cylinder models

Technical Specs

Product Type: Complete Piston Kit
Material: Cast Aluminum Alloy
Bore Size: 68mm (2.992") Standard
Stroke: 2-Stroke
Cylinder Configuration: 3-Cylinder
Product Dimensions: 8.0" L x 7.5" W x 7.5" H

What’s in the Box

1 x Piston
1 x Rings set
1 x Piston pin
2 x Circlips (pin clips)

Installation Notes

Disconnect the battery and ground the spark plug leads for safety.
Drain the engine coolant and oil completely.
Carefully remove the cylinder head and gasket to access the pistons.
Rotate the crankshaft to bring the piston to a workable position and remove the old piston pin and piston assembly.
Inspect the cylinder wall for wear, scoring, or damage. Hone the cylinder as needed to ensure a proper surface for the new rings.
Thoroughly lubricate the new piston, rings, and cylinder wall with fresh 2-stroke engine oil before installation.
Install the new piston and rings, ensuring ring gaps are correctly oriented according to your engine's service manual.
Reassemble all components with new gaskets, torquing all bolts to the manufacturer's precise specifications.
After reassembly, refill all fluids, reconnect the battery, and carefully check for any leaks before starting the engine.

Troubleshooting & FAQ

How do I confirm this kit fits my engine?

Check your engine's model, horsepower, and year against the compatibility table. The most reliable method is to cross-reference the OEM part number (779-96152 for Mercury/Mariner or 3C8-00004-0 for Tohatsu) from your existing piston or service manual.

What are common signs of a worn-out piston?

Symptoms include loss of compression, excessive smoke from the exhaust, a rattling or knocking sound from the engine (piston slap), and reduced overall performance or power.

Is honing the cylinder necessary before installing a new piston?

Yes, it is highly recommended to hone the cylinder walls. This process creates a specific cross-hatch pattern that helps the new piston rings seat correctly, which is essential for achieving optimal compression and engine performance.

Should I replace all pistons in my 3-cylinder engine at the same time?

For balanced performance, even compression, and long-term engine health, it is best practice to replace all pistons and rings simultaneously, especially if the engine has high hours or if one piston has already failed.

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.

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