Transom Seal Bellows Kit – Fits MerCruiser Alpha One Gen 2 (Replaces 30-803099T1)
Transom Seal Bellows Kit – Fits MerCruiser Alpha One Gen 2 (Replaces 30-803099T1) is backordered and will ship as soon as it is back in stock.
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Delivery and Shipping
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Transom Seal Bellows Kit – Fits MerCruiser Alpha One Gen 2 (Replace...
Product Details
This complete Transom Seal Bellows Kit – Fits MerCruiser Alpha One Gen 2 Stern Drives (Replaces 803099T1) is designed for MerCruiser Alpha One Generation 2 stern drives manufactured from 1991 and up (serial numbers 0D469859 and higher). It provides all the necessary components to seal the transom opening, protecting critical drive components from water intrusion.
This kit serves as a direct replacement for Mercury/MerCruiser 30-803099T1, Sierra 18-8206-1 / 18-8218, Mallory 9-72900 / 9-72904 / 9-72906, and Red Rhino MR-907.
- Installation: Mounts externally on the transom and gimbal housing.
- Housing Material: Made from durable neoprene rubber.
- Key Components: Includes drive, exhaust, and shift bellows, plus a gimbal bearing and gaskets.
Part Number Matrix
Use this matrix to confirm equivalent references across OEM and aftermarket.
| Brand | Part Number |
|---|---|
| Mercury/MerCruiser | 30-803099T1 |
| Mercury/MerCruiser | 803099T1 |
| Sierra | 18-8206-1 |
| Sierra | 18-8218 |
| Mallory | 9-72900 |
| Mallory | 9-72904 |
| Mallory | 9-72906 |
| Red Rhino | MR-907 |
Engine & Model Compatibility
Confirm your engine model/year in the table below.
| Brand | Model | Rated HP | Stroke | Years | OEM Part No. | Notes |
|---|---|---|---|---|---|---|
| MerCruiser | Alpha One Gen 2 | Various | 4-Stroke | 1991 and up | 803099T1/30-803099T1 | Serial numbers 0D469859 and up |
Technical Specs
- Product Type
- Transom Seal/Bellows Kit
- Installation
- External/Transom Mounted
- Connection
- Direct Mount to Transom/Gimbal Housing
- Housing Material
- Neoprene (Rubber)
- Housing Color
- Black
- Dimensions
- 12.32 × 7.44 × 6.18 inches (312.9 × 189 × 157 mm)
- Weight
- 4.4 pounds (2 kg)
- Fitting Type
- Mechanical Clamp
- Warranty
- Standard Manufacturer Warranty
- Other Technical Attributes
- Seals the transom opening between the boat and stern drive
What’s in the Box
- 1 × Drive Shaft Bellows (816431A1)
- 1 × Exhaust Bellows Assembly (18654A1/8M0124227)
- 1 × Shift Cable Bellows Assembly (74639A2)
- 1 × Gimbal Bearing (879194A02/30-879194A01/30-862540A3)
- 1 × Water Hose 3/4" (32-41725/32-8M0062309/8M0215001)
- 2 × Bell Housing Gasket Kit (27-94996T2/27-94996Q2/8M0091545)
- 1 × Gimbal Housing Oil Seal (26-88416)
- 1 × Gimbal Housing Seal (41802)
- 1 × Bell Housing Shaft Lever (45518A3)
- 1 × Shift Cable Guide (43433)
- 1 × Shift Cable Insert (14705)
- 1 × Shift Cable Wrapping (38473)
Installation Notes
- Safety first: Disconnect the boat's battery and ensure the stern drive is in the fully trimmed down position.
- Remove the stern drive assembly from the gimbal housing according to the manufacturer's service manual.
- Carefully remove the old bellows, gimbal bearing, and all associated seals and gaskets.
- Thoroughly clean all mating surfaces on the transom and gimbal housing, removing any old sealant or debris.
- Install the new gimbal bearing using an appropriate driver tool. Ensure it is seated correctly.
- Install the new drive shaft, exhaust, and shift cable bellows. Secure all clamps tightly.
- Install the new water hose and all included gaskets and seals.
- Reinstall the stern drive assembly, torquing all fasteners to the specified values.
- After reinstallation, check for proper shift and steering operation.
- Once the boat is in the water, check for any water leaks around the transom assembly.
Troubleshooting & FAQ
How do I know this kit fits my MerCruiser drive?
This kit is specifically for MerCruiser Alpha One Generation 2 stern drives made from 1991 onwards. The key identifier is the serial number, which must be 0D469859 or higher. Check your drive's serial number plate to confirm compatibility.
What are the signs that my transom bellows need replacing?
Common symptoms of failing bellows include visible cracks or dry rot on the rubber, water inside the boat bilge area (especially after use), and a grinding or roaring noise from the transom, which often indicates a failed gimbal bearing due to water intrusion.
What is the difference between Sierra 18-8206 and 18-8206-1?
While both are transom seal kits, the Sierra 18-8206-1 part number typically includes a greasable gimbal bearing, whereas the 18-8206 may include a non-greasable bearing. This kit is built to the specification of the greasable-bearing version for easier maintenance.
How often should these components be replaced?
As a general maintenance guideline, transom bellows should be inspected annually for cracks or damage and typically replaced every 3-5 years, depending on usage (freshwater vs. saltwater) and storage conditions.
Can I replace just one of the bellows instead of the whole kit?
While possible, it is highly recommended to replace all bellows and the gimbal bearing at the same time. The components are exposed to the same conditions and age at a similar rate. Replacing the full kit is a preventative measure that saves significant labor and cost down the line.
OEM vs. Aftermarket?
This listing is an aftermarket replacement (not OEM). Built to OEM-level specifications with comparable materials. Manufactured in an ISO 9002 facility, batch-inspected for consistency.
Shipping speed & cost
We ship worldwide quickly—typical transit 5–15 days. Standard shipping is free; expedited options appear at checkout where available.
Warranty & returns
Covered by a 1-year warranty against manufacturing defects under normal use. If issues arise, contact support with your order details. Returns are accepted within our standard window (unused & in original condition). See our policy page or reach out for instructions.
Safety & Important Info
- Verify images/specifications vs your original part. If anything differs—even if your model appears compatible—do not purchase.
- This is an aftermarket replacement, not an OEM component.
- Professional installation is recommended for safety and performance.
About Sea Sierra
- Pro-Grade Standards — We supply marine parts engineered to OEM-level tolerances and tested for real-world conditions.
- Fast Global Fulfillment — Free standard delivery to most regions in 5–15 days.
- Manufacturer-Direct Value — Fair pricing without compromising on materials or QC.
Payment & Security
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