U-Joint Bellows Kit – Fits MerCruiser Alpha One Gen II Drives (Replaces 816431A1, 18654A1, 74639Q02)
U-Joint Bellows Kit – Fits MerCruiser Alpha One Gen II Drives (Replaces 816431A1, 18654A1, 74639Q02) is backordered and will ship as soon as it is back in stock.
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Worry-free returns
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Delivery and Shipping
Delivery and Shipping
Free standard shipping on all orders under 1 KG
U-Joint Bellows Kit – Fits MerCruiser Alpha One Gen II Drives (Repl...
Product Details
This U-Joint Bellows Kit provides the essential components for servicing the transom assembly on MerCruiser Alpha One Gen II sterndrive units (1991–present). It is engineered to protect critical drivetrain components from water intrusion, ensuring long-lasting performance.
It serves as a direct replacement for MerCruiser part numbers 816431A1, 18654A1, and 74639Q02, as well as aftermarket equivalents including Sierra 18-2747, SBU 8M0124227, and GdlEpi GdlEpi63214.
- Made from durable, marine-grade rubber resistant to oil, gasoline, and saltwater.
- Kit includes U-joint, exhaust, and a shift bellows for a complete service.
- Engineered for a direct, OEM-style fit to simplify installation.
Part Number Matrix
Use this matrix to confirm equivalent references across OEM and aftermarket suppliers.
| Brand | Part Number |
|---|---|
| MerCruiser | 816431A1 |
| MerCruiser | 18654A1 |
| MerCruiser | 74639Q02 |
| Sierra | 18-2747 |
| SBU | 8M0124227 |
| GdlEpi | GdlEpi63214 |
Engine & Model Compatibility
Confirm your engine model and year in the table below to ensure correct fitment.
| Brand | Model | Rated HP | Stroke | Years | OEM Part No. | Notes |
|---|---|---|---|---|---|---|
| MerCruiser | Alpha One Gen II | All | 4-Stroke | 1991–Present | 816431A1 | For all Alpha One Gen II sterndrive applications |
Technical Specs
- Product Type
- U-Joint Bellows Kit
- Installation
- Direct replacement for specified MerCruiser drives
- Connection
- Secured with included stainless steel hose clamps
- Housing Material
- Marine-grade rubber
- Housing Color
- Black
- Dimensions
- 12.0 × 12.0 × 16.5 inches
- Weight
- 1.76 ounces (49.9 g)
- Fitting Type
- Direct OEM-style fit
- Other Technical Attributes
- Resistant to oil, grease, gasoline and water when installed with recommended adhesive
What’s in the Box
- 1 x Shift Bellows (74639Q02)
- 1 x Exhaust Bellows (18654A1)
- 1 x Universal Joint Bellows (816431A1)
- 1 x Sealing Gasket Kit (27-94996Q2)
Installation Notes
- Disconnect the battery and ensure the engine is off and cool before beginning work.
- Trim the sterndrive unit to the full "up" or "trailer" position to access the transom assembly.
- Carefully remove the old bellows, clamps, and any residual adhesive or gasket material.
- Thoroughly clean the mounting surfaces on the bell housing and transom assembly to ensure a clean seal.
- Apply a suitable marine-grade bellows adhesive to the mounting grooves on both the drive and the new bellows.
- Install the new U-joint, exhaust, and shift bellows, ensuring each is fully seated in its respective groove.
- Secure each bellows with the new stainless steel clamps provided, tightening them to the manufacturer's recommended torque specification.
- After installation, lower the sterndrive and inspect for proper alignment and a secure seal before operating the boat.
Troubleshooting & FAQ
Will this fit my MerCruiser Alpha One Gen I drive?
No, this kit is specifically designed for Alpha One Gen II sterndrives (1991–present). The components are not interchangeable with Gen I models.
What are the signs that my old bellows are failing?
Common signs include visible cracks, tears, or brittleness in the rubber. The most critical symptom of a failed U-joint bellows is finding water in the boat's bilge, which can lead to severe damage to the gimbal bearing and U-joints.
How often should I replace my sterndrive bellows?
As a crucial part of preventative maintenance, bellows should be inspected annually for any signs of wear or damage. It is recommended to replace them every 3–5 years, depending on usage and environmental conditions (saltwater vs. freshwater).
Is special adhesive required for installation?
Yes, using a high-quality marine bellows adhesive is essential to create a durable, waterproof seal. Not using the correct adhesive can lead to premature failure and water leaks.
Does this kit include a gimbal bearing or other hardware?
No, this kit contains the U-joint, exhaust, and shift bellows with their respective gaskets and clamps. The gimbal bearing and other transom service components must be purchased separately.
Can I just replace the one bellows that is leaking?
While technically possible, it is strongly recommended to replace all three bellows (U-joint, exhaust, shift) at the same time. They are exposed to the same conditions and have similar service lives, and the labor required to replace one is nearly the same as replacing all of them.
What’s the difference between OEM and aftermarket parts?
This listing is for an aftermarket replacement component, not an OEM part. It is built to meet or exceed OEM-level specifications with comparable materials and manufacturing standards. Our parts are produced in an ISO 9002 facility and are batch-inspected for quality and consistency.
How fast is shipping?
We ship worldwide, and typical transit time is 5–15 days for most regions. Standard shipping is free. Expedited shipping options, if available for your location, will be presented at checkout.
What is the warranty and return policy?
This product is covered by a 1-year warranty against manufacturing defects under normal use. If you encounter any issues, please contact our support team with your order details. Returns of unused items in their original condition are accepted within our standard return window.
Safety & Important Info
- Verify images and specifications against your original part before purchase. Do not install if anything differs, even if your model is listed as compatible.
- This is an aftermarket replacement part, not an original equipment manufacturer (OEM) component.
- Professional installation by a qualified marine mechanic is highly recommended for safety, performance, and to prevent damage.
About Sea Sierra
- Pro-Grade Standards — We supply marine parts engineered to OEM-level tolerances and rigorously tested for real-world conditions.
- Fast Global Fulfillment — We offer free standard delivery to most regions, with typical transit times of 5–15 days.
- Manufacturer-Direct Value — By working directly with manufacturers, we provide fair pricing without compromising on materials or quality control.
Payment & Security
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