Lower Unit Gearcase Seal Kit for Johnson/Evinrude 18–25 HP 2-Cylinder Outboards – Replaces Sierra 18-2684, GLM 87606, Mallory 9-74105
Lower Unit Gearcase Seal Kit for Johnson/Evinrude 18–25 HP 2-Cylinder Outboards – Replaces Sierra 18-2684, GLM 87606, Mallory 9-74105 is backordered and will ship as soon as it is back in stock.
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Delivery and Shipping
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Lower Unit Gearcase Seal Kit for Johnson/Evinrude 18–25 HP 2-Cylind...
Lower Unit Gearcase Seal Kit for Johnson/Evinrude 18–25 HP 2-Cylinder Outboards – Replaces Sierra 18-2684, GLM 87606, Mallory 9-74105 is backordered and will ship as soon as it is back in stock.
Product Details
This lower unit gearcase seal kit is designed for Johnson/Evinrude 2-cylinder, 18–25 HP outboard engines from 1958 through 1978. It provides the seals, gasket, O-rings, and drain/fill plug washers specified for servicing the lower unit gearcase.
The kit is an aftermarket replacement for Sierra 18-2684, GLM 87606, Mallory 9-74105, and EMP 26-01728. Johnson/Evinrude reference numbers associated with the included components are 304764, 321787, and 321788.
- For 1958–1978 Johnson/Evinrude 2-cylinder 18–25 HP outboards.
- Includes lower unit gearcase sealing components for a service or reseal procedure.
- Suitable for experienced DIY and professional marine repair work.
Part Number Matrix
Use these manufacturer and aftermarket references to compare the replacement kit with your existing part information.
| Brand or Source | Part Number | Reference Type |
|---|---|---|
| Sierra | 18-2684 | Aftermarket replacement reference |
| GLM | 87606 | Aftermarket replacement reference |
| Mallory | 9-74105 | Aftermarket replacement reference |
| EMP | 26-01728 | Aftermarket replacement reference |
| Johnson/Evinrude | 304764, 321787, 321788 | Component reference numbers |
Engine & Model Compatibility
Company fitment identifies this kit for Johnson/Evinrude 2-cylinder, 18–25 HP outboard engines manufactured from 1958 through 1978. Confirm the engine brand, cylinder configuration, horsepower, model year, and gearcase design before ordering.
| Brand | Engine Configuration | Rated HP | Stroke | Years | Application |
|---|---|---|---|---|---|
| Johnson/Evinrude | 2-cylinder outboard | 18–25 HP | Not specified in company fitment | 1958–1978 | Lower unit gearcase seal service |
Important: The available company fitment does not provide individual model numbers, serial-number ranges, shaft length, or a complete stroke breakdown. Match the complete engine and gearcase details rather than relying on horsepower alone.
Technical Specs
- Product Type
- Lower unit gearcase seal kit
- Application
- Johnson/Evinrude 2-cylinder 18–25 HP outboards, 1958–1978
- Installation
- DIY by an experienced installer or professional marine technician
- Product Classification
- Aftermarket replacement
What’s in the Box
- 1 × Shift rod gasket — Johnson/Evinrude reference 304764; aftermarket reference 18-0882
- 1 × Oil seal — Johnson/Evinrude reference 321788; aftermarket reference 18-2032
- 2 × Drain/fill plug washer — reference 311598; aftermarket reference 18-4248
- 1 × O-ring — reference 301877; aftermarket reference 18-7100
- 1 × O-ring — reference 307853; aftermarket reference 18-7120
- 1 × Oil seal — Johnson/Evinrude reference 321787; aftermarket reference 18-2031
- 1 × Spaghetti seal — reference 309044; aftermarket reference 18-2534
- 1 × O-ring — reference 321921; aftermarket reference 18-7411
- 1 × O-ring — reference 302493; aftermarket reference 18-7112
Quantities and component references above follow the company package listing. Compare the included components with your gearcase before beginning disassembly.
Installation Notes
- Place a suitable drain pan beneath the lower unit and drain the gear lubricant according to the engine service procedure.
- Remove the propeller and disconnect the shift linkage as required. Support the gearcase before removing the mounting hardware.
- Disassemble only the gearcase components necessary to access the seals, O-rings, gasket, and washers being replaced.
- Remove the old sealing components carefully and clean all mating and sealing surfaces.
- Compare each replacement component with the removed part and confirm its orientation before installation.
- Lubricate and install the new seals and O-rings using appropriate marine lubricant and seal-installation tools. Do not damage the sealing lips or housings.
- Reassemble the gearcase, reinstall the lower unit, reconnect the shift linkage, and tighten hardware to the applicable manufacturer service specifications.
- Refill the gearcase with the specified lubricant and install the drain/fill plugs with the supplied replacement washers.
- After operation, inspect the gearcase for lubricant leaks and check the lubricant for signs of water intrusion.
Always use the service manual for the specific engine model when setting shift linkage, torque values, seal orientation, and lubricant specifications.
Troubleshooting & FAQ
What are common signs of lower unit seal failure?
Water-contaminated gear lubricant may appear milky or cloudy. Lubricant around the propeller shaft, drain/fill plugs, or other gearcase sealing areas can also indicate a leak. Inspect the gearcase and follow the engine service procedure before replacing components.
How can I confirm that this kit fits my engine?
Confirm that your engine is a Johnson/Evinrude 2-cylinder outboard rated at 18–25 HP and within the 1958–1978 application range. Also compare the gearcase design and the component references with your existing parts. Individual model and serial-number coverage is not provided in the company fitment record.
Does this kit include every possible lower unit seal?
This kit includes the components listed in the “What’s in the Box” section. Gearcase designs and service requirements can vary, so compare the listed parts with your unit before disassembly. Additional components may be needed for a complete overhaul.
Is this an OEM kit?
No. This is an aftermarket replacement kit. The listed Johnson/Evinrude numbers identify component references, while Sierra, GLM, Mallory, and EMP numbers are aftermarket comparison references.
Should a professional install the kit?
Professional installation is recommended if you are not familiar with lower unit disassembly, seal installation, shift linkage adjustment, and gearcase lubricant service.
Safety & Important Information
- Verify the complete engine application and gearcase configuration before ordering.
- Do not rely on horsepower alone; model year, 2-cylinder configuration, and gearcase design must match.
- Use appropriate lifting, support, drain, and seal-installation procedures when working on the lower unit.
- This is an aftermarket replacement and is not manufactured by Johnson, Evinrude, Sierra, GLM, Mallory, or EMP.
About Sea Sierra
Sea Sierra supplies aftermarket marine replacement parts for maintenance and repair applications. Verify fitment and component references against your engine and the parts being replaced before installation.
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