Bellows Kit – Fits MerCruiser Alpha One Gen II (1991-Present) (Replaces 74639Q02, 816431A1, 18654A1, 27-94996Q2)
Bellows Kit – Fits MerCruiser Alpha One Gen II (1991-Present) (Replaces 74639Q02, 816431A1, 18654A1, 27-94996Q2) 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
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Bellows Kit – Fits MerCruiser Alpha One Gen II (1991-Present) (Repl...
Product Details
This comprehensive MerCruiser Alpha One Gen II Bellows Kit provides a complete sealing solution for MerCruiser Alpha One Generation II sterndrive systems (1991–Present). It is designed to prevent water intrusion into critical drive components, ensuring long-term reliability and performance.
This kit serves as a direct replacement, providing interchanges for MerCruiser shift cable bellows (74639Q02), U-joint bellows (816431A1), exhaust bellows (18654A1), and the bell housing gasket kit (27-94996Q2).
- Engineered for direct replacement installation.
- Constructed from durable, marine-grade rubber compounds for longevity.
- Includes all necessary stainless steel mounting hardware for a complete overhaul.
Part Number Matrix
Use this matrix to confirm equivalent references across OEM and aftermarket.
| Component | Replaces Part Numbers |
|---|---|
| Shift Cable Bellows | 74639Q02, 74639A2, 74369, 31659 |
| U-Joint Bellows | 816431A1, 60932A1, 60932A4 |
| Exhaust Bellows | 18654A1, 8M0124227, 32734A3, 32734 |
| Bell Housing Gasket Kit | 27-94996Q2, 27-94996A1, 27-94996T2, 27-64818A3 |
Engine & Model Compatibility
Confirm your engine model/year in the table below.
This kit is designed primarily for MerCruiser Alpha One Gen II models produced from 1991 to the present. Please verify your serial number for pre-1998 models.
| Brand | Model | Rated HP | Stroke | Years | OEM Part No. | Notes |
|---|---|---|---|---|---|---|
| MerCruiser | 3.0L | 135 HP | 4-Stroke | 1999–2016 | 74639Q02, 816431A1, 18654A1, 27-94996Q2 | Serial Number Ranges: 0D469859-0F679999 (1991-1995), 0F680000-0K999999 (1996-1997), 0L100040+ (1998 & Up) |
| MerCruiser | 4.3L | 190–220 HP | 4-Stroke | 1991–Present | 74639Q02, 816431A1, 18654A1, 27-94996Q2 | V6 Engine |
| MerCruiser | 5.0L | 220–260 HP | 4-Stroke | 1991–Present | 74639Q02, 816431A1, 18654A1, 27-94996Q2 | V8 Engine |
| MerCruiser | 5.7L | 250–300 HP | 4-Stroke | 1991–Present | 74639Q02, 816431A1, 18654A1, 27-94996Q2 | V8 Engine |
| MerCruiser | 350 Mag | 300 HP | 4-Stroke | 1991–Present | 74639Q02, 816431A1, 18654A1, 27-94996Q2 | 5.7L V8 Engine |
Compatibility with older MerCruiser R/MR series (1983–1990) requires a serial number of 6225577 or higher.
| Brand | Model | Rated HP | Stroke | Years | OEM Part No. | Notes |
|---|---|---|---|---|---|---|
| MerCruiser | 2.5L | 165 HP | 4-Stroke | 1983–1990 | 74639Q02, 816431A1, 18654A1, 27-94996Q2 | Serial Number 6225577 and higher only |
| MerCruiser | 3.7L | 170 HP | 4-Stroke | 1983–1990 | 74639Q02, 816431A1, 18654A1, 27-94996Q2 | Serial Number 6225577 and higher only |
| MerCruiser | 4.3L | 190 HP | 4-Stroke | 1983–1990 | 74639Q02, 816431A1, 18654A1, 27-94996Q2 | Serial Number 6225577 and higher only |
| MerCruiser | 5.7L | 260 HP | 4-Stroke | 1983–1990 | 74639Q02, 816431A1, 18654A1, 27-94996Q2 | Serial Number 6225577 and higher only |
Technical Specs
- Product Type
- Complete Bellows Maintenance Kit
- Installation
- Direct Replacement
- Housing Material
- Marine-Grade Rubber Compounds
- Connection
- OEM-Compatible Mounting Flanges
- Dimensions
- Varies by Component (OEM Specifications)
- Weight
- 1.1 kg (2.43 lbs)
- Operating Temperature
- Suitable for Marine Environment (-20°C to 60°C)
- Warranty
- 1-Year Against Manufacturing Defects
- Other Technical Attributes
- Includes Stainless Steel Mounting Hardware
What’s in the Box
- 1 x Shift Cable Bellows Assembly (74639Q02) with 2 Stainless Steel Hose Clamps
- 1 x U-Joint Bellows Assembly (816431A1) with Grounding Straps and Clamps
- 1 x Exhaust Bellows Assembly (18654A1/8M0124227) with 2 Stainless Steel Hose Clamps
- 1 x Bell Housing Installation Gasket Kit (27-94996Q2) (6-piece set)
Installation Notes
- Ensure the engine is off and the battery is disconnected for safety.
- Raise the sterndrive to the full "trailer" position to access the bellows assemblies.
- Carefully remove the old bellows and their clamps. Note the orientation of each component.
- Thoroughly clean all mating surfaces on the bell housing and gimbal ring, removing any old sealant or debris.
- Install the new gaskets from the bell housing kit onto the clean, dry surfaces.
- Fit the new U-joint, exhaust, and shift cable bellows. Secure them tightly with the provided stainless steel clamps.
- Ensure all connections are secure and properly seated. Reconnect any grounding straps.
- Lower the sterndrive and check for proper movement and sealing before operating the vessel in water.
Troubleshooting & FAQ
How do I know if this kit fits my MerCruiser sterndrive?
This kit is specifically for MerCruiser Alpha One Generation II drives (1991–Present). It also fits some later model R/MR drives (1983-1990) with serial number 6225577 and higher. Always verify your drive model and serial number range using the compatibility tables above.
What are the signs my old bellows are failing?
Common signs of failing bellows include visible cracks, brittleness, or holes in the rubber. The most critical symptom is water entering the bilge, which can indicate a leak in the U-joint or shift cable bellows and lead to catastrophic drive failure if not addressed.
How often should bellows be replaced?
As a preventative maintenance item, it is recommended to inspect bellows annually and replace them every 3–5 years, depending on usage (freshwater vs. saltwater) and storage conditions. If you see any signs of wear, replace them immediately.
Can I replace just one bellow, or should I do the whole kit?
While you can replace a single bellow, it is highly recommended to replace all of them at the same time. They are all made of similar materials and exposed to the same conditions, so if one has failed, the others are likely near the end of their service life.
Do I need special tools for installation?
Standard marine mechanic's tools are generally sufficient. However, a specialized bellows expander tool can make fitting the exhaust and U-joint bellows much easier. A quality clamp driver is also essential for proper tightening.
What’s the difference between OEM and this aftermarket part?
This listing is an aftermarket replacement, not an OEM component. It is built to meet or exceed OEM-level specifications with comparable high-quality materials. Our parts are manufactured in an ISO 9002 certified facility and are batch-inspected for quality and consistency.
What is the shipping speed and cost?
We ship worldwide quickly—typical transit time is 5–15 days. Standard shipping is free to most regions, with expedited options available at checkout where applicable.
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 are accepted within our standard window for unused items in their original condition. See our policy page or reach out for instructions.
Safety & Important Info
- Verify images and specifications against your original part before purchase. If anything differs—even if your model appears compatible—do not order.
- This is an aftermarket replacement part, not an OEM component. Brand names and part numbers are used for reference purposes only.
- Professional installation is strongly recommended for safety and to ensure optimal performance. Incorrect installation can lead to severe equipment 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.
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