Piston Ring Kit – Fits MerCruiser & Tohatsu M25/M30 (Replaces 39-16054A5, 346-00011-0)

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Piston Ring Kit – Fits MerCruiser & Tohatsu M25/M30 (Replaces 39-16054A5, 346-00011-0) is backordered and will ship as soon as it is back in stock.

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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.).

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Delivery and Shipping

Free standard shipping on all orders under 1 KG

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 Ring Kit is designed for select MerCruiser 2-cylinder marine inboard engines (2000s–present) and Tohatsu M25C3 and M30A4 2-cylinder outboard engines (2000s–present). It serves as a crucial component for engine rebuilds and maintenance, ensuring proper cylinder sealing and compression.

It directly replaces MerCruiser part numbers 39-16054A5, 39-8M0080349, and 8M0080349, as well as Tohatsu part number 346-00011-0.

Installation Type: Engine Service Part
Engine Type: For 2-Cylinder Gasoline Engines
Package includes one complete piston ring set.

Part Number Matrix

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

Brand	Part Number	Superseded By	Notes
MerCruiser	39-16054A5	39-8M0080349	Original part number.
MerCruiser	39-8M0080349	8M0080349	First supersession.
MerCruiser	8M0080349		Current part number.
Tohatsu	346-00011-0

Engine & Model Compatibility

Confirm your engine model/year in the table below.

For MerCruiser, this kit fits various 2-cylinder inboard engines manufactured from the 2000s to the present.

For Tohatsu, this kit is confirmed for M25C3 and M30A4 2-cylinder models.

Brand	Model	Rated HP	Stroke	OEM Part No.	Notes
MerCruiser	2-cylinder inboard engines		4-Stroke	39-16054A5	Superseded by 39-8M0080349, then 8M0080349
Tohatsu	M25C3	25	4-Stroke	346-00011-0	2-cylinder model
Tohatsu	M30A4	30	4-Stroke	346-00011-0	2-cylinder model

Technical Specs

Product Type: Piston Ring Kit
Installation: Engine Service Part
Fuel Type: Gasoline
Housing Material: Metal (Steel/Cast Iron)
Housing Color: Silver/Metallic
Dimensions: 7.5" L x 7.2" W x 1.0" H
Weight: 0.01 kg (0.022 lb)
Other Technical Attributes: For 2-cylinder engines
Warranty: Manufacturer standard warranty

What’s in the Box

1 x Piston Ring Set (Replaces 39-16054A5/39-8M0080349/8M0080349 or 346-00011-0)

Installation Notes

Disconnect the battery and ensure the engine is cool. Drain engine oil and coolant.
Remove the cylinder head, cylinder block, and other components to access the pistons.
Carefully remove the old piston from the connecting rod.
Using a ring expansion tool, remove the old piston rings.
Thoroughly clean the piston, paying special attention to the ring grooves.
Install the new rings onto the piston, ensuring they are in the correct order and orientation (check for markings).
Lubricate the piston, rings, and cylinder bore with fresh engine oil.
Use a ring compressor tool to carefully install the piston assembly back into the cylinder.
Reassemble the engine components according to the manufacturer's service manual, tightening all bolts to their specified torque.
Refill engine oil and coolant. Reconnect the battery and check for leaks before starting the engine.

Troubleshooting & FAQ

How do I know if my piston rings need replacing?

Common signs of failing piston rings include excessive blue or white smoke from the exhaust, high oil consumption between changes, and a noticeable loss of engine power or compression. A cylinder compression test can help diagnose the issue definitively.

Will this kit fit engine models not listed here?

We can only guarantee fitment for the models explicitly listed in the compatibility table. Using this kit on other models is not recommended, as even minor differences in engine design can lead to improper fit and engine damage.

Is a special tool required for installation?

Yes, professional installation is recommended. Specialized tools such as a piston ring expander (to safely remove and install rings without damaging them) and a piston ring compressor (to correctly insert the piston into the cylinder bore) are required.

Do these rings need to be gapped?

These rings are manufactured to standard OEM specifications. However, it is always best practice for the installer to verify the ring end-gap with a feeler gauge and file to fit if necessary, following the specific engine's service manual tolerances.

Do these rings have a specific orientation?

Yes. Piston rings often have a top and bottom side, indicated by a small dot, letter, or bevel on the ring's surface. The marking almost always faces up towards the top of the piston. Installing them upside down will lead to increased oil consumption and poor sealing.

Is there a break-in procedure after installation?

Yes. After a rebuild, it is crucial to follow a proper engine break-in procedure. This typically involves running the engine at varied, moderate RPMs without subjecting it to heavy loads for the first several hours of operation to allow the new rings to seat properly against the cylinder walls.

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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