Lower Unit Gasket and Seal Kit for Mercury/Mariner 25–30 HP 2-Stroke Outboards, 1984–1991 – Replaces 27-8M0089639 and 95220A1

Product Details

This lower unit gasket and seal kit is intended for selected Mercury and Mariner 2-stroke outboard engines, including 25 HP, 30 HP, and 25 Jet models from the 1984–1991 model years. It is used when servicing the gearcase and replacing worn or damaged gaskets, seals, and O-rings that can allow water intrusion or gear-oil leakage.

The kit is listed as an aftermarket replacement for Mercury/Mariner references including 27-8M0089639, 95220A1, 804908A01, 27-8M0089636, 41899M, and 27-41899M. Listed Yamaha cross-reference numbers are 689-W0001-22-00, 689-W0001-21-00, 689-W0001-C1-00, and 689-W0001-C2-00.

• For servicing the lower unit or gearcase.
• Includes a set of gaskets, seals, and O-rings for the applicable service configuration.
• Useful for routine maintenance, leak repair, or lower-unit rebuilding.
• Verify the engine model, year, serial-number range, and original part before ordering.

Part Number Matrix

The following references are listed for identification and cross-reference purposes. They should be compared with the number on the original component and the engine application before installation.

Engine and Model Compatibility

The applications below describe the listed compatibility range. Model codes, production variations, shaft configuration, and serial-number breaks may affect fitment. Confirm the exact model identification and original part number before purchase.

Technical Specifications

Product Type

Lower unit gasket and seal kit

Application

Lower unit / gearcase service

Engine Type

Selected Mercury and Mariner 2-stroke outboards

Listed Horsepower Range

25–30 HP, including selected 25 Jet models

Listed Model Years

1984–1991

Component Types

Gaskets, seals, and O-rings

Installation Notes

1. Place a drain pan beneath the gearcase. Remove the upper vent and lower drain screws and drain the gear lubricant.
2. Remove the fasteners securing the lower unit to the engine midsection.
3. Lower and detach the gearcase carefully. Disconnect the shift-shaft linkage first if required by the specific model.
4. Disassemble the lower unit only as far as necessary to access the applicable gaskets, seals, and O-rings.
5. Clean all mating surfaces and remove old gasket material and sealant residue without damaging the aluminum surfaces.
6. Compare each replacement component with the removed part, then install the applicable new gaskets, seals, and O-rings. Lubricate seals as appropriate for the installation.
7. Reassemble the gearcase and torque fasteners according to the engine manufacturer's service information.
8. Reinstall the lower unit, confirming correct alignment of the driveshaft, water tube, and shift shaft.
9. Refill the gearcase through the lower drain opening until lubricant reaches the upper vent opening.
10. Install the vent screw, then remove the fill pump and install the lower drain screw. Use the correct new drain-screw washers where required.

Troubleshooting and FAQ

Safety and Important Information

• Drain gear lubricant safely and dispose of used lubricant according to local regulations.
• Use the service manual for correct disassembly, seal orientation, fastener torque, and lubricant specifications.
• Do not force a component into place or reuse damaged sealing hardware.
• Confirm the parts and dimensions against the original components before installation.
• Professional installation is recommended when specialized gearcase tools or internal repairs are required.

About Sea Sierra

• Marine replacement parts — Parts selected for maintenance and repair applications across a range of marine engines.
• Application-focused listings — Model and part-number information is provided to help customers compare replacement components.
• Service support — Always verify the exact engine identification and original part before installation.