Upper Unit Seal Kit 26-88397A1 for MerCruiser Alpha One Gen II Stern Drive
Upper Unit Seal Kit 26-88397A1 for MerCruiser Alpha One Gen II Stern Drive
Product Overview
Upper unit seal kit for the MerCruiser Alpha One Gen II sterndrive, 15 sealing parts across 12 part types: 4 x oil seals, 8 x O-rings, 1 x check valve kit, 1 x seal ring gasket and 1 x drain screw washer. It replaces MerCruiser 26-88397A1 and crosses to Sierra 18-2644 and Mallory 87501, it covers the drives from 1991 to 1998 by serial number, and one kit ships at 61 g with packaging.
This is the kit for the upper housing, the section that carries the vertical driveshaft down from the engine coupler. Everything that keeps gear lube inside the top of the drive is in the bag: the seals on the driveshaft, the O-rings on the bearing carrier and the plugs, and the gasket under the seal ring.
MerCruiser is the sterndrive brand of Mercury Marine, and the seal set here is the factory one for the top of the drive rather than a generic O-ring assortment. Each size in the bag matches one bore in the housing.
Upper housing seals fail from the outside in. Water gets past the driveshaft seal on the front, the lube turns milky, and the first thing the owner notices is a drive that whines or a lube level that keeps rising. By then the upper bearings have already run on contaminated oil.
The kit is worth doing as a set because the parts come off together. Once the drive is split and the upper housing is on the bench, every seal in it is accessible, so fitting one and leaving the rest is a false economy.
Fitment is by drive serial number, not by engine model. MerCruiser built the Alpha One Gen II from 1991 and the serial ranges above tell you which production run your drive came from. Check the serial on the transom plate before ordering.
Specifications & Attributes
| Specification | Detail |
|---|---|
| Condition | New / New with tags |
| Type | Upper unit seal kit |
| MerCruiser Part Number | 26-88397A1 |
| Sierra Number | 18-2644 |
| Mallory Number | 87501 |
| Red Rhino Number | 9-74302 |
| SEI Number | 94-116-09K |
| OBR Number | MR-249 |
| Drive | MerCruiser Alpha One Gen II sterndrive |
| Fitment Method | By drive serial number |
| Years | 1991 to 1998 and later by serial |
| Parts In Kit | 15 pieces across 12 part types |
| Net Weight | 61 g including packaging |
| Packaging | Pack |
| Quantity | 1 kit |
| Warranty | 3 year |
OEM Cross Reference
| Brand | Part Numbers |
|---|---|
| MerCruiser | 26-88397A1 |
| Sierra | 18-2644 |
| Mallory | 87501 |
| Red Rhino | 9-74302 |
| SEI | 94-116-09K |
| OBR | MR-249 |
Compatible Engines
| Drive | Years | Serial Number Range |
|---|---|---|
| Alpha One Gen II | 1991 - 1995 | 0D469859 through 0F679999 |
| Alpha One Gen II | 1996 - 1997 | 0F680000 through 0K999999 |
| Alpha One Gen II | 1998 and up | 0L100040 and up |
What's Included
| Component | Detail | Qty |
|---|---|---|
| Oil seal | Driveshaft seal, upper housing | 1 |
| Oil seal | Second size in the upper housing | 2 |
| Check valve kit | For the upper housing vent | 1 |
| Seal ring gasket | Under the seal ring | 1 |
| Drain screw washer | For the drain and fill screws | 1 |
| Double lip seal | Upper housing | 1 |
| O-ring | Bearing carrier and housing joints | 2 |
| O-ring | Housing joint | 1 |
| O-ring | Housing joint | 1 |
| O-ring | Housing joint | 1 |
| O-ring | Housing joint | 1 |
| O-ring | Housing joint | 2 |
Key Features
| Feature | Detail |
|---|---|
| Complete upper seal set | 15 pieces covering the whole upper housing |
| Direct replacement | Fits in place of MerCruiser 26-88397A1 |
| Cross referenced | Sierra 18-2644, Mallory 87501, Red Rhino 9-74302 |
| Alpha One Gen II | Built for the drive from 1991 onward |
| Serial number fitment | Three ranges cover the whole production run |
| Check valve included | The vent valve comes in the kit |
Signs The Upper Seals Need Replacing
| What You See | What It Means | Action |
|---|---|---|
| Gear lube turns milky | Water getting past the driveshaft seal | Fit the kit |
| Lube level keeps rising | Water entering the upper housing | Fit the kit |
| Whine from the upper housing | Bearings running on contaminated lube | Fit the kit and inspect the bearings |
| Oil weeping at the top of the drive | Seal ring gasket or O-ring failed | Fit the kit |
| Drive being split for service | Seals are a service item | Fit the kit while it is apart |
| Lube on the transom after a run | Upper housing leaking | Fit the kit |
Fitting Notes
| Step | Action |
|---|---|
| 1 | Check the drive serial number against the table above |
| 2 | Drain the gear lube and check it for water or metal before you start |
| 3 | Take the drive off and split the upper and lower housings |
| 4 | Prise the old seals out and clean the bores without scoring them |
| 5 | Fit the new seals square, with the lip facing the lube side |
| 6 | Fit the O-rings with a light coat of gear lube so they seat without twisting |
| 7 | Refit the housing and torque the bolts to the manual figure |
| 8 | Fill with lube, run the drive and check the level and the colour again after the first trip |
Condition & Warranty
| Item | Detail |
|---|---|
| Condition | New / New with tags |
| Warranty | 3 year |
| Packaging | Pack |
Before You Buy
- Replaces MerCruiser 26-88397A1
- Crosses to Sierra 18-2644, Mallory 87501 and Red Rhino 9-74302
- Also listed as SEI 94-116-09K and OBR MR-249
- Fits the MerCruiser Alpha One Gen II sterndrive
- Fitment is by drive serial number, 1991 through 1998 and later
- 15 sealing parts across 12 part types
- One kit, gear lube not included
- 61 g with packaging
- 30-Day Easy Returns
- Free Worldwide Shipping
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Boat Owners' Review
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