Head Gasket – Fits Johnson/Evinrude 5–6 HP Outboards (Replaces OMC 329103, 306204)

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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

Sierra's 18-2961 head gasket is designed for use in Johnson and Evinrude outboard motors. It specifically fits 5, 5.5, and 6 HP engines manufactured from 1960 to 1979.

This part offers a direct interchange for Sierra 18-2961, GLM 33830, and Johnson/Evinrude OEM part numbers 306204 and 329103.

Designed for direct-fit installation.
Engineered to meet or exceed OEM specifications.
Suitable for gasoline-powered marine engines.

Part Number Matrix

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

Brand	Part Number
Sierra	18-2961
GLM	33830
Johnson/Evinrude	329103
Johnson/Evinrude	306204

Engine & Model Compatibility

Confirm your engine model/year in the table below.

For Johnson/Evinrude owners: This part fits a range of 2-stroke models produced from 1960–1979. Please verify your engine's horsepower and year to ensure compatibility.

Brand	Model	Rated HP	Stroke	Years	OEM Part No.
Johnson/Evinrude	Various	5	2-Stroke	1960–1979	329103, 306204
Johnson/Evinrude	Various	5.5	2-Stroke	1960–1979	329103, 306204
Johnson/Evinrude	Various	6	2-Stroke	1960–1979	329103, 306204

Technical Specs

Product Type: Cylinder Head Gasket
Installation: Direct replacement
Fuel Type: Gasoline
Housing Color: White
Dimensions: 18.0 x 14.0 x 0.3 inches
Weight: 1.28 ounces (36.3 g)
Warranty: Manufacturer's warranty
Other Technical Attributes: Meets or exceeds OEM specifications

What’s in the Box

1 x Head Gasket (329103, 306204)

Installation Notes

Ensure the engine is cool. Disconnect the battery and drain the cooling system as needed.
Remove the engine cover and any components that obstruct access to the cylinder head.
Following the manufacturer's service manual, loosen and remove the cylinder head bolts in the specified sequence to prevent warping the head.
Carefully lift the cylinder head off the engine block and remove the old head gasket.
Thoroughly clean both the cylinder head and engine block mating surfaces. Ensure all old gasket material and carbon deposits are removed.
Position the new head gasket correctly on the engine block. Do not use sealant unless explicitly required by your service manual.
Reinstall the cylinder head, then tighten the bolts to the proper torque specifications in the correct sequence.
Reassemble all previously removed components and reconnect the battery.
Start the engine and carefully check for any coolant or compression leaks around the head.

Troubleshooting & FAQ

How can I confirm this gasket fits my engine?

This gasket fits specific Johnson/Evinrude 5, 5.5, and 6 HP outboard models from 1960–1979. The best way to ensure fitment is to match your engine's original part number to one of the cross-references: Sierra 18-2961, GLM 33830, or OEM 329103 / 306204.

What are the signs of a failed head gasket on an outboard?

Common symptoms of a blown head gasket include a noticeable loss of power, white smoke from the exhaust, milky or frothy engine oil, water in the cylinders, or engine overheating. Performing a compression test is a reliable diagnostic step.

Should I use sealant with this replacement gasket?

In most cases, this head gasket is designed to be installed dry. Always consult your engine’s service manual for the manufacturer-recommended procedure, as some models may have unique requirements.

When should a head gasket be replaced?

A head gasket is not a routine maintenance part and should only be replaced when it fails. Its lifespan is influenced by engine condition, operating hours, and cooling system efficiency. Proper maintenance can help prevent premature failure.

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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