Transom Bellows Seal Kit – Fits MerCruiser Alpha One Gen II (Replaces 30-803099T1, 803099T1)
Transom Bellows Seal Kit – Fits MerCruiser Alpha One Gen II (Replaces 30-803099T1, 803099T1) is backordered and will ship as soon as it is back in stock.
Couldn't load pickup availability
Worry-free returns
Worry-free returns
You may return most new, unopened items within 7 days of delivery for a full refund. We'll also pay the return shipping costs if the return is a result of our error (you received an incorrect or defective item, etc.).
You should expect to receive your refund within four weeks of giving your package to the return shipper, however, in many cases you will receive a refund more quickly. This time period includes the transit time for us to receive your return from the shipper (5 to 10 business days), the time it takes us to process your return once we receive it (3 to 5 business days), and the time it takes your bank to process our refund request (5 to 10 business days).
If you need to return an item, simply login to your account, view the order using the "Complete Orders" link under the My Account menu and click the Return Item(s) button. We'll notify you via e-mail of your refund once we've received and processed the returned item.
Delivery and Shipping
Delivery and Shipping
Free standard shipping on all orders under 1 KG
Transom Bellows Seal Kit – Fits MerCruiser Alpha One Gen II (Replac...
Product Details
This Transom Bellows Seal Kit is designed for MerCruiser Alpha One Gen II stern drives manufactured from 1991 to the present (serial numbers 0D469859 and up). It provides the essential components needed to replace worn or damaged bellows, protecting your gimbal bearing and U-joints from water intrusion.
This kit serves as a direct replacement for Quicksilver part numbers 30-803099T1 and 803099T1, Sierra 18-8206-1 and 18-8218, and Mallory 9-72900 and 9-72906.
- Installation requires the removal of the outdrive assembly for access.
- Components are made from marine-grade rubber with stainless steel hose clamps for corrosion resistance.
- Note that bellows adhesive is required for installation but is not included with this kit.
Part Number Matrix
Use this matrix to confirm equivalent references across OEM and aftermarket.
| Brand | Part Number | Notes |
|---|---|---|
| Quicksilver | 30-803099T1 / 803099T1 | OEM Reference |
| Sierra | 18-8206-1 | Includes greasable gimbal bearing |
| Sierra | 18-8218 | Includes sealed gimbal bearing |
| Mallory | 9-72900 / 9-72906 |
Engine & Model Compatibility
Confirm your engine model/year in the table below.
For MerCruiser applications, it is critical to ensure your drive's serial number is 0D469859 or newer, in addition to matching the model and year range.
| Brand | Model | Rated HP | Stroke | Years | OEM Part No. | Notes |
|---|---|---|---|---|---|---|
| MerCruiser | Alpha One Gen II | All | 4-Stroke | 1991–Present | 30-803099T1/803099T1 | Serial numbers 0D469859 and up |
Technical Specs
- Product Type
- Transom Seal Kit / Bellows Kit
- Installation
- Direct replacement, requires removal of outdrive
- Housing Material
- Marine-grade rubber bellows with stainless steel hose clamps
- Housing Color
- Black
- Dimensions
- Varies by component
- Weight
- 2.2 kg (4.9 lbs)
- Warranty
- Limited lifetime (Sierra), Manufacturer warranty (Quicksilver)
- Other Technical Attributes
- California Prop 65 Warning applies
What’s in the Box
- 1 x U-Joint Bellows
- 1 x Exhaust Bellows
- 1 x Shift Cable Bellows
- 1 x Gimbal Bearing (Note: Greasable in Sierra 18-8206-1, Sealed in Sierra 18-8218)
- 1 x Water Hose (3/4" ID)
- Multiple x Stainless Steel Hose Clamps
- 1 x Mounting Gasket
- Multiple x Mounting O-Rings
Installation Notes
- Disconnect the vessel's battery and safely remove the outdrive assembly according to your manufacturer's service manual.
- Carefully cut and remove the old U-joint, exhaust, and shift cable bellows. Remove the old gimbal bearing.
- Thoroughly clean all mating surfaces on the transom and bell housing, removing any old adhesive or sealant residue.
- Press the new gimbal bearing into the gimbal housing, ensuring correct alignment for grease passage if applicable.
- Apply a suitable bellows adhesive (not included) to the mounting rings and install the new U-joint, exhaust, and shift bellows. Secure all connections with the provided clamps.
- Install the new water hose, mounting gasket, and O-rings.
- Carefully reinstall the outdrive assembly, checking for proper alignment and ensuring the U-joint shaft engages correctly.
- Before operating the vessel, perform a leak check by lowering the drive into the water and inspecting the bilge for any water intrusion.
Note: Bellows adhesive and gimbal bearing sealant are required for proper installation but are not included in this kit. Professional installation is highly recommended.
Troubleshooting & FAQ
Will this kit fit my MerCruiser Alpha One Gen II?
This kit is specifically designed for MerCruiser Alpha One Gen II stern drives manufactured from 1991 onwards. It is critical that you also verify your drive's serial number is 0D469859 or higher, as fitment depends on this range.
Is this a complete kit? What else will I need?
This kit contains all the necessary bellows, a gimbal bearing, gaskets, O-rings, and clamps. However, please note that bellows adhesive is required for a secure installation and is not included. Additionally, based on customer reports, the gimbal bearing seal is not included and is a recommended separate purchase.
What is the difference between the Sierra part numbers (18-8206-1 vs. 18-8218)?
The primary difference is the type of gimbal bearing included. Sierra kit 18-8206-1 contains a greasable gimbal bearing, which allows for periodic maintenance. Kit 18-8218 includes a sealed, non-greasable bearing. Your choice depends on your preference for a serviceable or maintenance-free component.
How do I know if my transom bellows are failing?
The most common signs of failure are visible cracks, splits, or dry rot on the rubber bellows during a visual inspection. A critical symptom is water leaking into your boat's bilge from the transom area, which indicates a breach and requires immediate attention to prevent severe damage to the U-joints and gimbal bearing.
Is this an original OEM part?
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.
What are the shipping speed & cost?
We ship worldwide quickly—typical transit 5–15 days. Standard shipping is free; expedited options appear at checkout where available.
What is the warranty and return policy?
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
Payment methods
Your payment information is processed securely. We do not store credit card details nor have access to your credit card information.
