Lower Unit Seal Kit for Select Mercury 9.9–25 HP Outboards — Replaces Mercury 26-85090A2
Lower Unit Seal Kit for Select Mercury 9.9–25 HP Outboards — Replaces Mercury 26-85090A2 is backordered and will ship as soon as it is back in stock.
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Lower Unit Seal Kit for Select Mercury 9.9–25 HP Outboards — Replac...
Lower Unit Seal Kit for Select Mercury 9.9–25 HP Outboards — Replaces Mercury 26-85090A2 is backordered and will ship as soon as it is back in stock.
Product Details
This aftermarket lower unit seal kit is designed to service the gear housing and propeller-shaft sealing areas on select Mercury outboard engines. It helps replace worn seals and restore protection against gear-lube leaks and water intrusion during lower-unit service.
The kit replaces Mercury OEM part 26-85090A2. The aftermarket reference Sierra 18-2624 is also commonly associated with this seal-kit application.
- Replacement seal kit for the lower unit, gear housing, and propeller-shaft service areas.
- Applicable to selected Mercury 9.9 HP, 15 HP, 20 HP, and 25 HP outboards listed below.
- Use the OEM part number, engine model, gear ratio, and serial-number range to confirm compatibility before ordering.
- Aftermarket replacement part; not manufactured by Mercury.
Part Number Matrix
These references identify the replacement part and an aftermarket cross-reference. Part-number correspondence does not replace verification of the engine serial-number range.
| Brand | Part Number | Role |
|---|---|---|
| Mercury | 26-85090A2 | OEM replacement reference |
| Sierra | 18-2624 | Aftermarket cross-reference |
Verified Mercury Catalog Applications
Mercury parts-catalog occurrences identify part 26-85090A2 as a seal kit in the following gear-housing and propeller-shaft diagrams. The listed serial ranges and gear-ratio conditions must remain together when checking fitment.
| Engine | Model / Configuration | Stroke | Serial Range | Gear Ratio / Diagram Condition | OEM Part No. |
|---|---|---|---|---|---|
| Mercury 9.9 HP | 9.9 4-Stroke, 323 cc | 4-Stroke | 0G760300 through 1B226999 | 2.42:1 gear ratio | 26-85090A2 |
| Mercury 9.9 HP | 9.9 4-Stroke, 323 cc | 4-Stroke | 0P075166 through 0P400999 | 2.42:1 gear ratio | 26-85090A2 |
| Mercury 15 HP | 15 4-Stroke | 4-Stroke | 0G590000 through 0G760299 | 2.42:1 gear ratio | 26-85090A2 |
| Mercury 15 HP | 15 4-Stroke | 4-Stroke | 0G760300 through 1B226999 | 2.42:1 gear ratio | 26-85090A2 |
| Mercury 15 HP | 15 4-Stroke | 4-Stroke | 0P401000 and up | 2.42:1 gear ratio, BigFoot | 26-85090A2 |
| Mercury 15 HP | 15 Sea Pro (XD) | Not specified | 9927000 through 0P016999 | 2.25:1 gear ratio | 26-85090A2 |
| Mercury 15 HP | 15 Sea Pro (XD) | Not specified | 0P017000 through 0P325499 | 2.25:1 gear ratio | 26-85090A2 |
| Mercury 20 HP | 20, 2-cylinder | Not specified | 0B238464 through 0G044026 | Gear housing / propeller-shaft assembly | 26-85090A2 |
| Mercury 20 HP | 20, 2-cylinder | Not specified | 0G044027 through 0G760299 | 2.25:1 gear ratio | 26-85090A2 |
| Mercury 20 HP | 20, 2-cylinder | Not specified | 0G760300 through 0T979999 | 2.25:1 gear ratio | 26-85090A2 |
| Mercury 20 HP | 20, 2-cylinder | Not specified | 0A730007 and up | Gear housing / propeller-shaft assembly | 26-85090A2 |
| Mercury 20 HP | 20 Jet | Not specified | 0G044027 through 0G760299 | 2.25:1 gear ratio | 26-85090A2 |
| Mercury 25 HP | 25, 2-cylinder | Not specified | 0T980000 through 0T999999 | 2.25:1 gear ratio | 26-85090A2 |
| Mercury 25 HP | 25, 2-cylinder | Not specified | 1B000001 and up | 2.25:1 gear ratio | 26-85090A2 |
| Mercury 25 HP | 25, 2-cylinder | Not specified | 0P325500 and up | 2.25:1 gear ratio | 26-85090A2 |
| Mercury 25 HP | 25, 25 Sea Pro, Super 15 | Not specified | 0B238464 through 0G044026 | Gear housing / propeller-shaft assembly | 26-85090A2 |
| Mercury 25 HP | 25, 25 Sea Pro, Super 15 | Not specified | 0G044027 through 0G760299 | 2.25:1 gear ratio | 26-85090A2 |
| Mercury 25 HP | 25, 25 Sea Pro, Super 15 | Not specified | 0G760300 through 0T979999 | 2.25:1 gear ratio | 26-85090A2 |
| Mercury 25 HP | 25, 25 Sea Pro, Super 15 | Not specified | 0A730007 and up | Gear housing / propeller-shaft assembly | 26-85090A2 |
| Mercury 25 HP | 25 H.P. Lightning, 3-cylinder, international | Not specified | 0E268781 through 0E287999 | Gear-housing assembly, propeller shaft | 26-85090A2 |
| Mercury 25 HP | 25 H.P. Lightning, 3-cylinder, international | Not specified | 0E288000 and up | Gear-housing assembly, propeller shaft | 26-85090A2 |
Technical Specifications
- Product Type
- Lower unit seal kit
- Replacement Reference
- Mercury 26-85090A2
- Aftermarket Cross-Reference
- Sierra 18-2624
- Service Area
- Gear housing and propeller-shaft sealing areas
- Brand Status
- Aftermarket replacement; not an OEM Mercury part
- Year Range
- Not specified; verify by model and serial number
What's in the Box
- 1 x lower unit seal kit
- Seal components for the applicable lower-unit service identified by the replacement reference
Exact seal shapes and quantities should be compared with the original parts and the applicable service diagram before installation.
Installation Notes
- Confirm the OEM part number, engine model, gear ratio, and serial-number range before beginning work.
- Drain the gearcase lubricant completely and dispose of it according to local requirements.
- Remove the propeller and related hardware as required for access to the propeller-shaft sealing area.
- Remove the lower unit according to the engine manufacturer's service procedure.
- Disassemble only the components necessary to access the failed seals and gaskets.
- Remove old seals carefully with a suitable seal-removal tool to avoid damaging the housing, shafts, or sealing bores.
- Clean and inspect all sealing surfaces, shafts, bores, and mating components for wear or damage.
- Lightly lubricate replacement seals and O-rings with the lubricant specified by the service manual, where applicable.
- Install each replacement seal squarely and to the correct depth using an appropriate seal driver.
- Reassemble the lower unit and torque fasteners according to the manufacturer's service specifications.
- Install the correct new drain and vent washers where required, then refill the gearcase with the specified lubricant.
- Check for leaks and verify proper gearcase operation before returning the outboard to service.
Troubleshooting & FAQ
Will this kit fit every Mercury or Mariner 9.9–25 HP outboard?
No. The documented applications are specific Mercury models and serial-number ranges, and the applicable gear ratio or lower-unit configuration must also match. Do not rely on horsepower alone. Confirm that your original part is 26-85090A2 or that your service documentation identifies this part.
Are both 2-Stroke and 4-Stroke engines covered?
The catalog records explicitly identify some 4-Stroke applications, while several 20 HP and 25 HP records do not state the stroke designation. Because stroke, gear ratio, model configuration, and serial range are not interchangeable, verify your exact engine information before ordering.
Are Mariner engines confirmed by the listed applications?
The available catalog records reviewed for this listing identify Mercury applications. A Mariner engine may share components with a Mercury model, but Mariner compatibility should be confirmed by matching the OEM part number and the complete model and serial information.
What are common signs of lower-unit seal failure?
Possible signs include milky or foamy gear lubricant, water contamination, lubricant around the propeller shaft, or lubricant leakage from the gear housing. Fishing line around the propeller shaft can damage seals and should be removed promptly.
Is special equipment required?
Basic hand tools may be sufficient for some work, but a seal puller, suitable seal driver, torque wrench, and the correct service information are recommended. Lower-unit disassembly can affect critical clearances and should be performed by a qualified technician when necessary.
Is this an OEM part?
No. This is an aftermarket replacement for Mercury OEM reference 26-85090A2.
Safety & Important Information
- Verify the complete model, serial number, gear ratio, and OEM part number before purchase.
- Do not assume compatibility from horsepower, brand, or appearance alone.
- Use the manufacturer's service manual for disassembly, seal orientation, torque values, lubricant specifications, and final testing.
- Professional installation is recommended because incorrect lower-unit assembly can cause water intrusion, lubricant loss, or gearcase damage.
- This product is an aftermarket replacement and is not affiliated with or endorsed by Mercury Marine.
About Sea Sierra
- Marine Replacement Parts — We offer aftermarket components for routine service and repair applications.
- Fitment-Focused Listings — Product references and application details are provided to help customers compare their original parts and engine information.
- Service-Oriented Support — Always compare the part number and complete engine details before installation.
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