18-2684 Lower Unit Seal Kit for Johnson Evinrude | JLM Marine

Lower Unit Seal Kit – Fits Johnson/Evinrude 18–25 HP Outboards (1958–1978)

This comprehensive lower unit seal kit is engineered for Johnson and Evinrude outboard engines ranging from 18 to 25 HP, covering model years 1958 through 1978. Designed specifically for 2-cylinder 3.000 bore crossflow configurations and 25 HP gear cases, this kit delivers reliable sealing performance to protect your lower unit gearcase from water intrusion and maintain proper lubrication.

This aftermarket replacement kit directly replaces OEM part numbers 18-2684, 87606, and 9-74105, providing a cost-effective solution for rebuilding or servicing your lower unit without compromising on quality.

• Complete seal kit for lower unit gearcase maintenance and rebuild
• Fits multiple Johnson/Evinrude HP ratings across a 20-year production span
• All seals and components required for proper lower unit service included

Part Number Cross-Reference

Use this table to confirm equivalent part numbers across OEM and aftermarket brands:

Compatible Engine Models

Confirm your engine model/year in the table below. For Johnson/Evinrude owners, here's a guide to help you identify your engine's serial/model: Johnson/Evinrude Serial Number Guide.

Technical Specifications

Package Contents

This complete seal kit includes:

• 1 × Seal Kit Lower Unit Gearcase
• The package contains all the seals and components shown in the product images.

Installation Guide

1. Drain the lower unit: Remove the drain and vent plugs and allow all gearcase oil to drain completely into a suitable container.
2. Remove the lower unit: Disconnect the shift linkage and unbolt the lower unit from the midsection following your engine's service manual.
3. Disassemble the gearcase: Carefully remove the propeller shaft, drive shaft, and associated gears, taking note of shim locations and orientation.
4. Remove old seals: Use a seal puller or pick to carefully extract all worn seals from the gearcase housing without damaging sealing surfaces.
5. Clean all surfaces: Thoroughly clean seal bores and mating surfaces, removing all old sealant, debris, and corrosion.
6. Install new seals: Lubricate new seals with gearcase oil and press them squarely into place using appropriate seal drivers or sockets.
7. Reassemble the gearcase: Install gears, shafts, and shims in reverse order, ensuring proper mesh and end play per factory specifications.
8. Reinstall the lower unit: Align the drive shaft splines and shift linkage, then bolt the lower unit securely to the midsection.
9. Refill with gearcase oil: Use the recommended marine gear oil and fill through the lower plug until oil appears at the vent hole.
10. Check for leaks: Run the engine in a test tank or on the water and inspect all seal areas for signs of oil leakage.

Troubleshooting & FAQ

Q: How do I know if this seal kit fits my specific Johnson or Evinrude outboard?
A: Cross-reference your engine's HP rating and year with the compatibility table above. This kit fits 18–25 HP models from 1958–1978, specifically 2-cylinder 3.000 bore crossflow engines and 25 HP gear cases. Verify your OEM part number matches 18-2684, 87606, or 9-74105.

Q: How often should I replace the lower unit seals?
A: Lower unit seals should be inspected annually and replaced every 2–3 years or whenever you notice milky oil (indicating water intrusion), oil leaks, or during any lower unit rebuild or repair.

Q: What are the signs that my lower unit seals are failing?
A: Common symptoms include gearcase oil that appears milky or contaminated with water, visible oil leaks around the propeller shaft or lower unit, difficulty shifting, or unusual noise from the lower unit during operation.

Q: Can I install this seal kit myself or do I need a professional?
A: While experienced DIY mechanics can perform this work, lower unit service requires specialized tools (seal drivers, bearing pullers), torque specifications, and careful attention to shim placement and gear timing. Professional installation is recommended if you lack experience with lower unit rebuilds.

Q: What's the difference between this aftermarket kit and the OEM Johnson/Evinrude kit?
A: This listing is an aftermarket replacement part (not an OEM component). We build to OEM specifications using comparable-grade materials. Production is done in an ISO9002-certified facility, and each batch is inspected for consistent performance.

Q: How fast do you ship and how much does it cost?
A: We offer fast global shipping—typically 5–15 days worldwide—and standard shipping is free. Expedited options are available at checkout depending on your location.

Q: What is your warranty and return policy?
A: This product includes a 1-year warranty against manufacturing defects under normal use. If something goes wrong, contact our support team with your order details. Returns are accepted within our standard return window (unused & in original condition); please see our policy page or reach out for instructions.

Important Notes

• Verify that the product images and specifications match your original part. If discrepancies exist—even if your model is listed—do not proceed with the purchase.
• This product is an aftermarket replacement part and is not an OEM component.
• Professional installation is recommended to ensure safety and optimal performance.

Why Choose JLM MARINE?

• Quality Assured: As a trusted manufacturer for over 20 years, we supply top marine brands globally.
• Fast Global Shipping: Free delivery worldwide in 5–15 days.
• Direct from Manufacturer: Competitive pricing without compromising quality.