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30-803097T1 Transom Seal Kit for MerCruiser Alpha One Gen I | JLM Marine
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Part Number Cross-Reference
- Mercury / MerCruiser OEM: 30-803097T1, 30-803097A2, 30803097T1, 803097T1
- Sierra Marine: 18-2601, 18-2601-1, 18-8213
- GLM: 21950
- SEI Marine: 9A-108
- Mallory Marine: 9-72902, 9-72904
- Engineered Marine Products (EMP): 61-08397
- Pro Marine: 68397
- OBR Red Rhino: MR-902
- WSM: 576-210
Important Fitment Exclusions
- Does NOT fit MerCruiser Alpha One Gen II drives (1991 and newer, serial numbers 0D469859 and up). Gen II drives require kit 30-803099T1.
- Does NOT fit Bravo drives (I, II, III) or Blackhawk drives.
- Does NOT fit units configured with an exhaust tube instead of exhaust bellows (different kit required).
- Does NOT fit older models prior to 1983 (serial numbers below 6225577).
Tip: If your drive has a plastic U-joint shaft cover, if the upper and lower housings are fastened together with through bolts rather than studs, or if the trim cylinders are mounted with C-clips instead of nuts, it is likely a Gen II — this kit will not fit. Gen II drives are also physically larger with a different shift shaft and larger water pump.
Quick Fitment Check: This complete transom seal kit is commonly listed for MerCruiser R, MR, Alpha One Gen I, and Alpha One SS sterndrives (approx. 1983–1990, serial number 6225577 & up) equipped with exhaust bellows. Replaces OEM 30-803097T1 and Sierra 18-2601-1.
Compatibility Guide
Use this compatibility guide as a reference only. Compatibility may vary by engine model, drive type, and serial number. Always verify your drive serial number before ordering.
| Drive Family | Years (Approx.) | Serial Number Range | Notes |
|---|---|---|---|
| MerCruiser R / MR | 1983 – 1990 | 6225577 & Up | With exhaust bellows |
| MerCruiser Alpha One Gen I | 1983 – 1990 | 6225577 & Up | With exhaust bellows |
| MerCruiser Alpha One SS | 1986 – 1989 | 0A545004 & Up | With exhaust bellows |
What's Included & Specifications
Kit Contents
- 1 x U-Joint Bellows Assembly (replaces 60932A4)
- 1 x Exhaust Bellows (replaces 18654A1 / 32734A3)
- 1 x Shift Cable Bellows (replaces 74639 / 74639A2)
- 1 x Gimbal Bearing — Greasable (replaces 30-60794A4 / 30-60794A2)
- 1 x 3/4" Water Intake Hose (replaces 32-32461)
- 1 x 5/8" Water Intake Hose (replaces 32-41725-33)
- 1 x Transom Bell Housing Gasket Set (replaces 27-94996A1 / 27-94996T2)
- Stainless Steel Hose Clamps and Mounting O-Rings
Package contents may vary slightly; please confirm with product photos.
Specifications
- Drive Type: MerCruiser R, MR, Alpha One Gen I, Alpha One SS
- Exhaust Configuration: With Exhaust Bellows
- Bearing Type: Greasable (zerk fitting compatible)
- Material: Marine-Grade Rubber / Stainless Steel
- Hose Sizes: 3/4" and 5/8" included
- Weight: Approx. 5.4 lbs
- Condition: Brand New — Aftermarket
Product Overview
Transom bellows are the primary barrier keeping water out of your boat's hull and engine compartment. They naturally degrade from UV exposure, marine growth, heat cycling, and constant flexing during trim and steering operations. A cracked U-joint bellows is one of the most common — and most expensive — failures on MerCruiser sterndrives.
What happens if you don't replace it? Water enters through the compromised seal, rapidly corroding the gimbal bearing and U-joints. Left unchecked, this leads to catastrophic water intrusion. The cost of replacing rusted U-joints, a seized gimbal bearing, and repairing water damage can easily exceed $2,000–$3,000 in parts and labor.
Replacing the complete transom seal kit during routine maintenance (typically every 3–5 years, or sooner if you notice any cracking) is a fraction of the cost of emergency repairs. This comprehensive service kit includes all essential components for a complete transom rebuild, saving you time and multiple shipping costs.
Top Features / Key Benefits
- Marine-Grade Rubber Construction: Engineered to resist UV degradation, saltwater exposure, and heat cycling — helping prevent the costly water intrusion that destroys U-joints and engine compartments.
- Complete Service Kit: Includes all bellows, hoses, bearing, gaskets, and clamps — no need to source parts individually, saving you time and multiple shipping costs.
- Universal Hose Fitment: Includes both 5/8" and 3/4" water intake hoses to ensure proper fitment regardless of your specific engine configuration.
- Direct Replacement: Designed as a direct replacement for OEM part 30-803097T1 and listed aftermarket equivalents, suitable for routine marine maintenance.
- Greasable Gimbal Bearing: Allows routine lubrication via zerk fitting, extending bearing life and reducing long-term maintenance costs.
- Stainless Steel Hardware: All included hose clamps are stainless steel for corrosion resistance in saltwater environments.
Installation Notes
- Difficulty Level: Advanced — requires removing the outdrive unit and specialized tools. Typical installation time is 2–6 hours depending on experience.
- Required Tools: Bellows expansion tool (e.g., 91-45497A1), hinge pin tool, engine alignment tool, slide hammer kit (for gimbal bearing removal), and a 1/4" wobble extension with 1/4" or 5/16" socket.
- Pro Tip: Apply marine-grade bellows adhesive (like Quicksilver 92-86166Q1 or Sierra #18-9031) to the U-joint, shift cable, and exhaust bellows to prevent them from coming loose when the drive is tilted. Do NOT get adhesive on the teeth of the housing.
- Pro Tip: Ensure hose clamp screws are positioned correctly before tightening so they don't rub against the bellows when the drive is trimmed up.
- Recommended Co-Replacement: While the sterndrive is removed, consider replacing the lower shift cable, water pump impeller kit, trim limit switch, and trim sender to avoid repeating this labor-intensive job. Replacing all components simultaneously is highly recommended.
Frequently Asked Questions
What's the difference between the Gen I and Gen II transom seal kit?
The Gen I kit (30-803097T1) fits MerCruiser Alpha One drives manufactured approximately 1983–1990 with serial numbers 6225577 and up. The Gen II kit (30-803099T1) fits Alpha One Gen II drives from 1991 and newer (serial 0D469859 and up). The two are NOT interchangeable — the bellows dimensions, shift cable bellows design, and mounting points are different. If your drive has a plastic U-joint shaft cover, 6 transom assembly bolts instead of 4, or trim cylinders mounted with C-clips, it's likely a Gen II.
Does this kit include the exhaust bellows?
Yes. This is the complete kit with exhaust bellows included. It contains the U-joint bellows, exhaust bellows, shift cable bellows, gimbal bearing, both water intake hoses (5/8" and 3/4"), transom gasket set, and all necessary stainless steel clamps and O-rings.
How often should I replace my MerCruiser transom bellows?
Most marine mechanics recommend inspecting transom bellows every 2 years and replacing them every 3–5 years, or immediately if you notice any cracking, hardening, or signs of water intrusion. Boats stored in the water year-round or operated in saltwater may need more frequent replacement.
Can I install this transom seal kit myself, or do I need a mechanic?
This is an advanced DIY job that requires specialized tools (bellows expander, hinge pin tool, alignment tool, slide hammer) and familiarity with sterndrive removal. If you have mechanical experience and the proper tools, it's achievable in 4–6 hours. If you're unfamiliar with the process, we recommend hiring a certified marine mechanic — improper installation can lead to water leaks.
Why does this kit include two different water hoses?
The kit includes both a 5/8" and a 3/4" water intake hose because different engine and drive configurations use different hose sizes. You will only use the one that matches your current setup — check your existing hose diameter before installation.
Is the gimbal bearing in this kit greasable or sealed?
This kit includes a greasable gimbal bearing with a zerk fitting. This allows routine lubrication through the transom assembly's grease fitting, which extends bearing life significantly compared to sealed bearings that cannot be maintained.
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.
Related JLM Marine Parts
- MerCruiser Alpha One Lower Shift Cables
- MerCruiser Alpha One Water Pump Impeller Kits
- Bellows Adhesive & Marine Lubricants
- Bellows Expansion Tools & Hinge Pin Tools
- All MerCruiser Alpha One Gen I Parts
Fitment Disclaimer: Compatibility may vary by engine model, drive type, and serial number. We strongly recommend verifying your engine/drive serial number against the OEM part numbers listed above before ordering. When in doubt, compare with your original part or consult your service manual.
We can ship to virtually any address in the world with free shipping available for most regions.
For our typical US and Canadian customers , our shipping timeframes are as follows:
- Amazon FBA: orders will be delivered within 1-5 business days after placing the order (during certain special periods such as major promotions, Christmas, etc., the delivery time of Amazon FBA may be affected).
- US warehouse shipment: orders will be delivered within 5 days after placing the order.
- China warehouse shipment: orders will be delivered about 12 days after placing the order.
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Please also note that the shipping rates for many items we sell are weight-based. The weight of any such item can be found on its detail page. To reflect the policies of the shipping companies we use, all weights will be rounded up to the next full pound.
Founded in 2002, JLM Marine has established itself as a dedicated manufacturer of high-quality marine parts, based in China. Our commitment to excellence in manufacturing has earned us the trust of top marine brands globally.
As a direct supplier, we bypass intermediaries, which allows us to offer competitive prices without compromising on quality. This approach not only supports cost-efficiency but also ensures that our customers receive the best value directly from the source.
We are excited to expand our reach through retail channels, bringing our expertise and commitment to quality directly to boat owners and enthusiasts worldwide.
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