26-85090A1 Lower Unit Seal Kit for Mercury 2 Cyl 18 2 Cyl 2.562 Bore 25 | JLM Marine

Lower Unit Seal Kit for Mercury 2 Cyl 18 / 2 Cyl 2.562 Bore 25 HP Outboards

This comprehensive lower unit seal kit is engineered for Mercury 2-cylinder outboard motors, specifically the 18 HP (1979-1987) and 25 HP 2.562 bore (1980-1983) models. Designed to restore proper sealing and prevent fluid leaks in your lower unit gearcase, this kit ensures reliable performance and extends the life of your outboard's drive system.

This aftermarket replacement kit directly replaces Mercury OEM part numbers 26-85090A1 and 18-2629, delivering the same fit and function at exceptional value. Whether you're performing routine maintenance or addressing a leak, this complete seal kit provides all the components you need for a thorough lower unit rebuild.

• Complete seal kit with all necessary gaskets, seals, and O-rings for lower unit service
• Prevents water intrusion and gear oil leakage for optimal gearcase protection
• Direct-fit replacement for Mercury lower units—no modification required

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 Mercury owners, here's a guide to help you identify your engine's serial/model: Mercury Serial Number Guide. You can also review exploded diagrams to verify part numbers: Mercury Parts Diagrams & Catalog.

Technical Specifications

Package Contents

This complete lower unit seal kit includes:

• 1x Lower Unit Seal Kit
• The package contains all the parts shown in the product images

Installation Guide

1. Disconnect the battery and remove the lower unit from the outboard following your service manual. Drain all gear oil completely and inspect for metal particles or contamination.
2. Clean all mating surfaces thoroughly, removing old gasket material and sealant residue. Inspect housings for cracks or damage.
3. Remove the old propeller shaft seals, input shaft seals, and all O-rings from their respective housings. Note the orientation of lip seals during removal.
4. Lubricate new seals with gear oil before installation. Install new propeller shaft seals with lips facing inward to retain oil.
5. Install new input shaft seals, ensuring proper seating in the bore. Use a seal driver or appropriate socket to avoid damage.
6. Replace all O-rings in shift shaft, water tube, and drain/fill plug locations. Lightly coat O-rings with gear oil for easier assembly.
7. Apply marine-grade gasket sealant to housing gaskets as needed per manufacturer specifications. Install gaskets carefully to align all bolt holes.
8. Reassemble the lower unit components, torquing all fasteners to factory specifications in the correct sequence. Follow your service manual's torque values.
9. Reinstall the lower unit onto the outboard, ensuring proper alignment of shift linkage and water tube. Secure all mounting bolts evenly.
10. Refill the lower unit with the proper grade and quantity of gear oil. Use the bottom drain plug to fill until oil appears at the upper vent hole.
11. Install and torque both drain and vent plugs with new crush washers if applicable. Wipe exterior clean and check for leaks.
12. Run the engine in a test tank or on the water, then recheck fluid level and inspect all seal areas for leakage after initial operation.

Troubleshooting & FAQ

Q: How do I know if my lower unit seals need replacement?
A: Common signs include gear oil leaking from the propeller shaft area, milky or contaminated gear oil (indicating water intrusion), excessive oil consumption, or visible oil residue around the lower unit housing. If you notice any of these symptoms, inspect and replace seals promptly to prevent internal damage.

Q: How often should I replace lower unit seals?
A: Lower unit seals should be inspected annually and replaced every 2-3 years or whenever you notice leakage or water contamination. If you frequently operate in saltwater or harsh conditions, more frequent replacement may be necessary. Always replace seals during any lower unit rebuild or gearcase repair.

Q: Can I reuse any of the old seals or gaskets?
A: No, always replace all seals, gaskets, and O-rings when servicing the lower unit. Reusing old seals can result in leaks, water intrusion, and potential gear damage. This kit provides all necessary components for a complete, leak-free rebuild.

Q: What's the difference between this aftermarket kit and the OEM Mercury 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.