Hinge Pin Tool – Fits Mercury Mercruiser Alpha One, Gen II & Bravo Sterndrives (Replaces 91-78310, 18-9861)
Hinge Pin Tool – Fits Mercury Mercruiser Alpha One, Gen II & Bravo Sterndrives (Replaces 91-78310, 18-9861) is backordered and will ship as soon as it is back in stock.
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Delivery and Shipping
Delivery and Shipping
Orders are typically processed within 1–2 business days.
U.S. orders usually arrive within 6–15 days, depending on stock location and destination.
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Hinge Pin Tool – Fits Mercury Mercruiser Alpha One, Gen II & Br...
Hinge Pin Tool – Fits Mercury Mercruiser Alpha One, Gen II & Bravo Sterndrives (Replaces 91-78310, 18-9861) is backordered and will ship as soon as it is back in stock.
Product Details
This Hinge Pin Tool is designed for the removal and installation of hinge pins on Mercury Mercruiser sterndrives, including Alpha One (Gen I & II), Bravo (I, II, & III), MC-1, R, and MR models from 1975 to the present. The tool is used on the hinge pin bolts to separate the sterndrive housing from the gimbal ring, simplifying service and maintenance.
It serves as a direct aftermarket replacement for Mercury part 91-78310, Sierra 18-9861, GLM 90200, and Mallory 9-79805.
- Engineered from hardened steel with a black oxide coating for durability.
- Features a 12-point socket for a secure fit on the hinge pin bolt.
- Designed for manual use with a standard ratchet or breaker bar.
Part Number Matrix
Use this matrix to confirm equivalent references across OEM and aftermarket.
| Brand | Part Number |
|---|---|
| Mercury | 91-78310 |
| Sierra | 18-9861 |
| GLM | 90200 |
| Mallory | 9-79805 |
Engine & Model Compatibility
Confirm your engine model/year in the table below.
For Mercury Mercruiser Sterndrives, this tool applies to the gimbal ring hinge pins on the following units.
| Model | Application | Years | OEM Part No. |
|---|---|---|---|
| Alpha One | Sterndrive Units | 1975–1990 | 91-78310 |
| Alpha One Gen II | Sterndrive Units | 1991–Present | 91-78310 |
| Bravo I | Sterndrive Units | All | 91-78310 |
| Bravo II | Sterndrive Units | All | 91-78310 |
| Bravo III | Sterndrive Units | All | 91-78310 |
| MC-1 | Sterndrive Units | All | 91-78310 |
| R | Sterndrive Units | All | 91-78310 |
| MR | Sterndrive Units | All | 91-78310 |
Technical Specs
- Product Type
- Hinge Pin Removal/Installation Tool
- Material
- Hardened Steel with Black Oxide Coating
- Connection
- 12-Point Socket End
- Function
- Removal and installation of hinge pin from drives
- Application
- Used on hinge pin bolts to separate housing from gimbal ring
- Installation
- Hand Tool - Use with Ratchet or Breaker Bar
- Dimensions
- Approx. 52 × 16 × 16 mm (2.05 × 0.63 × 0.63 in)
- Weight
- 0.06 kg (2.11 oz)
What’s in the Box
- 1 × Hinge Pin Tool (Replaces 91-78310 / 18-9861)
Installation Notes
- Ensure the engine is off and the battery is disconnected for safety.
- Trim the sterndrive to the full up position to access the hinge pins.
- Place the hinge pin tool onto the pin bolt head securely.
- Attach a standard ratchet or breaker bar to the tool.
- Apply steady, even pressure to loosen and remove the hinge pin bolt.
- Clean the threads and surrounding area before installing the new pin.
- Use the tool to carefully thread in and tighten the new hinge pin bolt.
- Torque the bolt to the manufacturer's recommended specification.
Troubleshooting & FAQ
Which Mercruiser drives is this tool specifically for?
This tool is designed for a wide range of Mercruiser sterndrives, including Alpha One (both Gen I and Gen II), all Bravo models (I, II, and III), MC-1, R, and MR drives from 1975 to the present.
How does this tool work?
The tool fits over the hinge pin bolts that connect the sterndrive housing to the gimbal ring. By attaching a ratchet or breaker bar, you can apply the necessary torque to loosen or tighten these specific bolts for removal or installation.
What is the difference between this tool and the OEM part 91-78310?
This is an aftermarket tool designed to meet or exceed the specifications of the original OEM tool. It performs the same function and is made from comparable hardened steel materials but is available at a more competitive price point.
What are the signs that my hinge pins need service?
Common symptoms include excessive play or looseness in the sterndrive, difficulty steering, or unusual noises while turning or trimming the drive. A visual inspection may also reveal corrosion or wear on the pins.
The tool isn't fitting the hinge pin bolt correctly. What could be the issue?
First, confirm you are working on a compatible Mercruiser model. Check for corrosion or damage on the bolt head that may be preventing a secure fit. Ensure the tool's 12-point socket end is clean and free of debris.
Is this tool necessary for replacing the gimbal bearing?
Yes, removing the sterndrive housing from the gimbal ring is a required step for accessing and replacing the gimbal bearing. This tool is essential for that process.
What is the difference between OEM and aftermarket parts?
This listing is an aftermarket replacement (not OEM). Built to OEM-level specifications with comparable materials. Manufactured in an ISO 9002 facility, batch-inspected for consistency.
What are the shipping speed and cost?
We ship worldwide quickly—typical transit 5–15 days. Standard shipping is free; expedited options appear at checkout where available.
What is your warranty and returns policy?
Covered by a 1-year warranty against manufacturing defects under normal use. If issues arise, contact support with your order details. Returns are accepted within our standard window (unused & in original condition). See our policy page or reach out for instructions.
Safety & Important Info
- Verify images/specifications vs your original part. If anything differs—even if your model appears compatible—do not purchase.
- This is an aftermarket replacement, not an OEM component.
- Professional installation is recommended for safety and performance.
About Sea Sierra
- Pro-Grade Standards — We supply marine parts engineered to OEM-level tolerances and tested for real-world conditions.
- Fast Global Fulfillment — Free standard delivery to most regions in 5–15 days.
- Manufacturer-Direct Value — Fair pricing without compromising on materials or QC.
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