SIERRA 18-1117 Pinion Bearing 31-42647A1 Qty.

( Brand: Sierra ), ( Manufacturer Part Number: 18-1117 ), ( Part Type: Pinion Bearing ), ( Country Of Origin: United States )

Review SIERRA Mercury Pinion Bearing Qty. Part fits MARINE

The **Mercury Marine Pinion Bearing (Part Number: 31-42647A1)** from the **Sierra 18** outboard engine series is a precision-engineered component designed to ensure smooth, reliable, and long-lasting performance in demanding marine applications. This high-quality bearing is a critical part of the outboard s transmission system, specifically serving as the pinion bearing within the gearcase, where it supports the pinion gear an essential component that transfers power from the engine s output shaft to the propeller. Crafted from durable, heat-resistant materials, this bearing is engineered to withstand the intense stresses of high torque, constant vibration, and exposure to saltwater corrosion, which can accelerate wear in marine environments. Its robust construction minimizes friction and wear, reducing the risk of premature failure and extending the operational lifespan of the entire drive system. The pinion bearing operates under extreme conditions, including rapid acceleration, deceleration, and sustained load-bearing during cruising, fishing, or towing, making its reliability indispensable for maintaining optimal engine efficiency and power delivery. Whether used in recreational boats, fishing vessels, or utility crafts, this bearing ensures that the Sierra 18 s outboard delivers the torque and responsiveness expected from a Mercury Marine engine, known for its durability and performance. Proper installation and regular maintenance, such as checking for excessive play or unusual noise, are recommended to preserve the bearing s integrity and prevent costly repairs.

**Pros and Cons of buying a Mercury Marine Pinion Bearing (Part Number: 31-42647A1) for a Sierra 18 Outboard Motor**

### **Pros**

1. **Compatibility and Fit**: This part is specifically designed for the Mercury 4.6L V8 outboard engines, including the Sierra 18 series. It ensures a proper fit, reducing the risk of installation issues or premature wear.

2. **Performance Reliability**: Pinion bearings are critical components that support the drive shaft and transfer power from the engine to the propeller. A high-quality bearing like this one helps maintain smooth operation, reducing vibration and potential damage to other engine components.

3. **Durability**: Mercury Marine parts are known for their durability and resistance to wear, especially in marine environments where exposure to saltwater, moisture, and varying temperatures can accelerate degradation. This bearing is likely built to withstand these conditions.

4. **Ease of Installation**: Since it is an OEM (Original Equipment Manufacturer) part, it should be straightforward to install, assuming the user has basic mechanical skills or access to a professional mechanic. Replacement is often a relatively simple procedure compared to major engine overhauls.

5. **Warranty Coverage**: Purchasing directly from Mercury or an authorized dealer may include warranty protection, offering peace of mind in case of defects or premature failure.

6. **Preventative Maintenance**: Replacing a worn pinion bearing as part of routine maintenance can prevent catastrophic engine failure, which can be costly and time-consuming to repair.

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### **Cons**

1. **Cost**: Replacement parts for marine engines, especially OEM components, can be expensive. The pinion bearing itself may not be the most costly part of the job, but labor costs for installation could add up if professional help is required.

2. **Labor-Intensive Replacement**: While not overly complex, replacing a pinion bearing often requires removing the lower unit (the part of the outboard that houses the drive shaft and propeller), which can be labor-intensive. This may involve draining fluids, disconnecting components, and ensuring proper alignment.

3. **Potential for Counterfeit Parts**: If purchasing from a non-authorized seller, there is a risk of receiving a counterfeit or low-quality part. Counterfeit parts may fail prematurely or not fit correctly, leading to further damage or safety hazards.

4. **Additional Wear Indicators**: If the pinion bearing is failing, it may be accompanied by other worn components (e.g., gears, seals, or the lower unit housing). Replacing just the bearing might not fully resolve underlying issues, and additional repairs could be necessary.

5. **Time and Downtime**: Replacing the bearing requires removing the outboard from the boat, which means the boat may be out of commission for several hours or even days, depending on the complexity of the job and whether other repairs are needed.

6. **Skill Dependency**: If the user lacks mechanical experience, attempting the replacement themselves could lead to mistakes, such as improper lubrication, misalignment, or damage to surrounding components. In such cases, hiring a professional may be necessary, increasing costs.

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### **Conclusion**

The Mercury Marine pinion bearing (31-42647A1) is a high-quality, reliable component that is essential for the smooth and efficient operation of your Sierra 18 outboard engine. Its compatibility, durability, and role in preventative maintenance make it a worthwhile investment for maintaining engine health. However, the cost, labor requirements, and potential for additional underlying issues must be considered. If the bearing is failing or showing signs of wear (e.g., unusual noise, vibration, or difficulty shifting), replacing it promptly is advisable to avoid more extensive damage.

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### **Recommendation**

1. **Verify the Need**: Confirm that the pinion bearing is indeed the source of the problem. Symptoms like grinding noises, difficulty shifting, or excessive vibration may indicate other issues (e.g., worn gears, lower unit damage, or misalignment). Consult a marine mechanic if unsure.

2. **Purchase from Authorized Sources**: Buy the part directly from Mercury Marine, an authorized dealer, or a reputable marine parts supplier to ensure authenticity and warranty coverage.

3. **Budget for Labor**: If you are not experienced with outboard repairs, factor in the cost of professional installation. Many marine mechanics charge by the hour, and the job may take 2-4 hours depending on the complexity.

4. **Consider a Full Lower Unit Inspection**: If replacing the pinion bearing, take the opportunity to inspect other components in the lower unit (e.g., gears, seals, and bearings) for wear. Addressing these issues proactively can extend the life of your engine.

5. **Follow Maintenance Guidelines**: After replacement, follow Mercury Marine s maintenance recommendations, including regular oil changes, fluid checks, and inspections. Proper lubrication and care will help ensure the new bearing lasts as long as possible.

6. **Document the Repair**: Keep records of the replacement, including the part number, date, and any work performed. This documentation can be useful for warranty claims or future troubleshooting.

**Final Verdict**: If the pinion bearing is confirmed to be faulty and you prioritize the longevity and reliability of your Sierra 18 outboard, replacing it with the Mercury Marine OEM part is a sound decision. However, weigh the costs and effort against the benefits, and consider whether addressing other potential issues simultaneously would be more cost-effective in the long run.

Details:

1 Make: SIERRA Part #: 31-42647A1 18-1117, This is a band new part in factory packaging.

part #: 181117 prices

• $41.39-$449.99

specifications ouboaen:

• for models: Marine
• for makes: Mercury
• brand: Sierra
• mpn: 18-1117
• part type: Pinion Bearing
• country of origin: United States

returns ouboaen:

• time: 30 Days
• policy: Returns Accepted
• paid by: Seller

payments ouboaen:

• credit card: Diners-club
• wallet: Apple-pay
• other

offer ouboaen:

• best offers: True
• options: Ship-to-home
• quantity: 1
• availability: In Stock
• sold: 0
• started: April 19, 2026

seller ouboaen:

• rating: 98.6%
• # reviews: 2777
• city: Sale Creek, Tennessee

shipping ouboaen:

• class: Standard
• service: USPS First Class, FedEx Ground / FedEx Home Delivery, UPS Ground
• type: Fixed
• carrier: USPS, FedEx, UPS
• transit: 5-11 Days
• cost: $7.95

general ouboaen:

• Boat Parts > Outboard Engines Components > Other
• condition: New

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