Transom Bellows Seal Kit – Fits MerCruiser Alpha One Gen II (Replaces 30-803099T1, 803099T1)

Transom Bellows Seal Kit – Fits MerCruiser Alpha One Gen II

This transom bellows seal kit is designed for MerCruiser Alpha One Gen II stern drives manufactured from 1991 and newer, specifically fitting serial numbers 0D469859 and up. It serves as a comprehensive service kit to replace essential components that prevent water from entering the vessel through the transom assembly.

This kit is a direct replacement for several OEM and aftermarket part numbers, ensuring compatibility and a proper fit for your sterndrive maintenance needs.

• Complete Kit: Includes U-joint, exhaust, and shift bellows, along with a gimbal bearing, water hose, and necessary hardware.
• Direct Replacement: Engineered to replace Quicksilver 30-803099T1, Sierra 18-8206-1, and others.
• Installation Note: The installation process requires the removal of the outdrive.

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. For Mercury owners, here’s a guide to help you identify your engine’s serial/model: Mercury Serial Number Guide. You can also review exploded diagrams to verify part numbers: Mercury Parts Diagrams & Catalog.

Technical Specifications

Package Contents

• 1 x U-Joint Bellows
• 1 x Exhaust Bellows
• 1 x Shift Cable Bellows
• 1 x Gimbal Bearing (Available with Greasable or Sealed bearing)
• 1 x Water Hose (3/4" ID)
• Multiple x Stainless Steel Hose Clamps
• 1 x Mounting Gasket
• Multiple x Mounting O-Rings
• Note: This kit does not include the gimbal bearing seal, which is recommended and should be purchased separately.
• Note: Bellows adhesive is required for installation but is not included in this kit.

Installation Guide

1. Safety First: Disconnect the boat's battery before beginning any work.
2. Remove the Outdrive: Shift the unit into forward gear. Remove the trim ram bolts and the six mounting nuts to detach the outdrive from the transom assembly.
3. Remove Old Bellows: Carefully cut and remove the old U-joint, exhaust, and shift cable bellows. Remove the hose clamps holding them in place.
4. Remove Gimbal Bearing: Use a slide hammer and bearing puller attachment to remove the existing gimbal bearing from the housing.
5. Clean Surfaces: Thoroughly clean the bell housing and transom assembly surfaces where the new bellows and gasket will sit.
6. Install Gimbal Bearing: Use a gimbal bearing installation tool to drive the new bearing into place, ensuring it is properly aligned.
7. Install Bellows: Apply bellows adhesive to the mounting surfaces. Install the new shift cable, exhaust, and U-joint bellows.
8. Secure Bellows: Secure each bellows with the new stainless steel hose clamps provided, ensuring a tight fit.
9. Install Water Hose: Replace the raw water intake hose.
10. Reinstall Outdrive: Apply a new gasket and reconnect the outdrive to the transom assembly, tightening the six nuts to the manufacturer's torque specifications. Reattach the trim rams.

Troubleshooting & FAQ

Q: How do I confirm this fits my engine?
A: This kit is specifically for MerCruiser Alpha One Gen II sterndrives made from 1991 onwards. The most important factor is the serial number, which must be 0D469859 or higher. Please verify your serial number before purchasing.

Q: What is the difference between the Sierra 18-8206-1 and 18-8218 kits?
A: The primary difference is the type of gimbal bearing included. The Sierra 18-8206-1 kit comes with a greasable gimbal bearing, which has a grease fitting allowing for periodic maintenance. The Sierra 18-8218 kit contains a sealed gimbal bearing that does not require greasing.

Q: Are there any common issues I should be aware of during installation?
A: Some users have reported that the aftermarket U-joint bellows can be thicker than the OEM version, occasionally making it difficult to reinstall the outdrive. Additionally, please note that this kit does not include bellows adhesive or a gimbal bearing seal, which are required for a complete installation and should be sourced separately.

Q: What are the signs that my transom bellows need to be replaced?
A: The most common signs of failing bellows are visible cracks in the rubber, brittleness, or water leaking into the bilge area. A faulty U-joint bellow can lead to catastrophic failure of the gimbal bearing and U-joints if water intrudes.

Q: OEM vs. Aftermarket?
A: This listing is an aftermarket replacement part (not an OEM component). We build to OEM specifications using comparable-grade materials. Production is done in an ISO9002-certified facility, and each batch is inspected for consistent performance.

Q: How fast do you ship and how much does it cost?
A: We offer fast global shipping—typically 5–15 days worldwide—and standard shipping is free. Expedited options are available at checkout depending on your location.

Q: What is your warranty and return policy?
A: This product includes a 1-year warranty against manufacturing defects under normal use. If something goes wrong, contact our support team with your order details. Returns are accepted within our standard return window (unused & in original condition); please see our policy page or reach out for instructions.

Important Notes

• Verify that the product images and specifications match your original part. If discrepancies exist—even if your model is listed—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.

Why Choose JLM MARINE?

• Quality Assured: As a trusted manufacturer for over 20 years, we supply top marine brands globally.
• Fast Global Shipping: Free delivery worldwide in 5–15 days.
• Direct from Manufacturer: Competitive pricing without compromising quality.