Head Gasket – Fits Johnson Evinrude 25-35 HP (Replaces OMC 319633, 777428, 35840, Sierra 18-2954, GLM 35840)
Head Gasket – Fits Johnson Evinrude 25-35 HP (Replaces OMC 319633, 777428, 35840, Sierra 18-2954, GLM 35840) is backordered and will ship as soon as it is back in stock.
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Worry-free returns
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.).
You should expect to receive your refund within four weeks of giving your package to the return shipper, however, in many cases you will receive a refund more quickly. This time period includes the transit time for us to receive your return from the shipper (5 to 10 business days), the time it takes us to process your return once we receive it (3 to 5 business days), and the time it takes your bank to process our refund request (5 to 10 business days).
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Delivery and Shipping
Delivery and Shipping
Free standard shipping on all orders under 1 KG
Head Gasket – Fits Johnson Evinrude 25-35 HP (Replaces OMC 319633, ...
Product Details
This aftermarket Head Gasket – Fits Johnson Evinrude 25-35 HP is engineered to restore a reliable seal for 2-stroke outboard engines from 1976–1978. It is designed for specific 25 HP and 35 HP models, ensuring proper fit and function for 2-cylinder applications.
It serves as a direct replacement for OMC part numbers 319633, 777428, and 35840, and interchanges with Sierra 18-2954 and GLM 35840.
- Designed for 2-cylinder engines
Part Number Matrix
Use this matrix to confirm equivalent references across OEM and aftermarket.
| Brand | Part Number |
|---|---|
| OMC | 319633 |
| OMC | 777428 |
| OMC | 35840 |
| Sierra | 18-2954 |
| GLM | 35840 |
Engine & Model Compatibility
Confirm your engine model/year in the table below.
For Johnson and Evinrude owners, please verify your engine's horsepower, stroke, and year fall within the ranges listed. Comparing your original part number is the best way to guarantee fitment.
| Brand | Model | Rated HP | Stroke | Years | OEM Part No. | Notes |
|---|---|---|---|---|---|---|
| Johnson/Evinrude | All | 25 | 2-Stroke | 1977–1978 | 319633 | |
| Johnson/Evinrude | All | 35 | 2-Stroke | 1976–1978 | 319633 | |
| Johnson/Evinrude | 25RL78C | 25 | 2-Stroke | 1978 | 319633 | |
| Johnson/Evinrude | 25E78C | 25 | 2-Stroke | 1978 | 319633 | |
| Johnson/Evinrude | 35RL78R | 35 | 2-Stroke | 1978 | 319633 | |
| Johnson/Evinrude | 35652G | 35 | 2-Stroke | 1978 | 319633 |
Technical Specs
- Product Type
- Head Gasket
- Designed For
- 2-cylinder engines
- Dimensions
- Height: 5.5 in; Width: 11.0 in; Length: 1.13 in
What’s in the Box
- 1 x Gasket for Outboard (Replaces 319633)
Installation Notes
- Disconnect the battery and spark plug wires for safety.
- Drain the engine coolant completely.
- Carefully remove the cylinder head cover and any connected components.
- Remove the old head gasket and thoroughly clean both the engine block and cylinder head surfaces. Ensure they are free of old gasket material, oil, and debris.
- Position the new head gasket correctly, confirming alignment with all bolt holes and passages. Do not use sealant unless specified by your engine's service manual.
- Reinstall the cylinder head and torque the bolts to the manufacturer's specifications in the correct sequence.
- Reconnect all components, refill the coolant, and re-attach the battery and spark plug wires.
- Start the engine and check for any leaks.
Troubleshooting & FAQ
How do I know if this head gasket fits my engine?
The best way to ensure correct fitment is to match the OEM part number from your old gasket to one of the numbers in our Part Number Matrix (e.g., 319633). Also, check your engine's model, horsepower, and year against the compatibility table provided.
Is this for 2-cylinder or 3-cylinder engines?
This head gasket is specifically designed for 2-cylinder Johnson/Evinrude engines. While some online listings may mention "3-Cylinder," our data confirms it fits the 2-cylinder models produced in the specified horsepower and year ranges.
What are the signs of a failed outboard head gasket?
Common symptoms include loss of engine compression, a milky or foamy appearance in the engine oil (indicating water intrusion), engine overheating, and visible water leaking from the cylinder head joint.
Do I need to apply sealant when installing this gasket?
Most modern head gaskets are designed to be installed dry without any additional sealant. Applying sealant can interfere with the gasket's ability to create a proper seal. Always follow the specific instructions in your engine's official service manual.
How often should a head gasket be replaced?
Head gaskets are not a routine maintenance item. They are typically replaced only when they fail or during a complete engine overhaul or rebuild.
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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