26-88397A1 Upper Gearcase Seal Kit for Mercruiser Alpha One Gen II | JLM Marine

Upper Gearcase Seal Kit for Mercruiser Alpha One Gen II – 26-88397A1

This comprehensive upper gearcase seal kit is engineered to fit Mercruiser Alpha One Gen II stern drives from 1991 and up. Designed to restore proper sealing and prevent gear oil leaks, this kit provides all the essential seals, o-rings, and gaskets needed for a complete upper gearcase service.

This aftermarket replacement kit directly replaces OEM part number 26-88397A1 and cross-references with Sierra 18-2644, GLM 87501, and Mallory 9-74302, ensuring broad compatibility and reliable performance.

• Complete seal and gasket kit for Alpha One Gen II drive shaft housing
• Includes oil seals, o-rings, check valve kit, and drain/fill gaskets
• Fits serial number ranges 0D469859 through 0L100040 and up (1991-1998+)

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.

Technical Specifications

Package Contents

This complete seal kit includes the following components:

• (1) 18-2003 Oil Seal
• (2) 18-2056 Oil Seal
• (1) 18-2715 Check Valve Kit
• (1) 18-2944 Seal Ring Gasket
• (1) 18-2945 Drain Screw Gasket
• (1) 18-3289 Double Lip Seal
• (2) 18-7103 O-Ring
• (1) 18-7117 O-Ring
• (1) 18-7161 O-Ring
• (1) 18-7169 O-Ring
• (1) 18-7188 O-Ring
• (2) 18-7420 O-Ring

Installation Guide

1. Preparation: Remove the stern drive unit from the boat following manufacturer service manual procedures. Drain all gear oil completely and clean the external surfaces.
2. Disassembly: Separate the upper gearcase from the lower unit. Remove the drive shaft and inspect for wear or damage.
3. Remove Old Seals: Carefully extract all old seals, o-rings, and gaskets from the drive shaft housing. Clean all sealing surfaces thoroughly with solvent and inspect for scoring or corrosion.
4. Install New Seals: Lubricate new oil seals with gear oil before installation. Press seals into their housings squarely using the appropriate seal driver tool to avoid distortion.
5. Install O-Rings: Install new o-rings in their respective grooves, ensuring they are not twisted or pinched. Lightly coat with gear oil for easier assembly.
6. Install Gaskets: Place the new seal ring gasket and drain screw gasket in their correct positions. Do not use additional sealant unless specified by the service manual.
7. Install Check Valve: Install the check valve kit according to manufacturer specifications, ensuring proper orientation and seating.
8. Reassembly: Carefully reassemble the drive shaft housing, ensuring all components are properly aligned. Torque all fasteners to factory specifications.
9. Reinstall Drive: Mount the stern drive back onto the transom assembly. Reconnect all shift and throttle linkages according to service manual.
10. Fill with Gear Oil: Fill the gearcase with the correct type and quantity of marine gear oil. Check for proper oil level at both drain and vent holes.
11. Leak Check: Run the engine in a test tank or on the water and inspect for any oil leaks around seal areas. Re-torque drain plug if necessary.
12. Final Inspection: After initial operation, recheck oil level and inspect again for leaks. Monitor gear oil condition after the first few hours of use.

Troubleshooting & FAQ

Q: How do I confirm this kit fits my specific Alpha One Gen II drive?
A: Verify your stern drive serial number against the compatibility table above. Serial numbers 0D469859 through 0L100040 and up (1991-1998+) are compatible. The serial number plate is typically located on the transom assembly.

Q: What are the signs that my upper gearcase seals need replacement?
A: Common indicators include gear oil leaking from the upper drive shaft housing, milky or contaminated gear oil (indicating water intrusion), low gear oil levels between services, or visible oil residue around seals during inspection.

Q: How often should I replace the upper gearcase seals?
A: Replacement intervals vary based on usage, but most manufacturers recommend inspecting seals annually and replacing them every 3-5 years or whenever disassembling the drive for service. Replace immediately if leaks or damage are detected.

Q: Can I reuse any of the old seals or o-rings during reassembly?
A: No, always replace all seals, o-rings, and gaskets when servicing the upper gearcase. Reusing old seals can result in oil leaks and water contamination, leading to costly internal damage.

Important Notes

• Verify that the product images and specifications match your original part. If discrepancies exist, 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.