Mercury Quicksilver Cotter Pin 18-54929 | Gimbal Ring & Lower Swivel Pin Retainer – MerCruiser Alpha One Gen II & Bravo

Gimbal Ring & Lower Swivel Pin Cotter Pin for MerCruiser Sterndrives

The Mercury Quicksilver 18-54929 is an OEM split cotter pin used to lock the gimbal ring, hinge pin, and lower swivel pin hardware in place on select MerCruiser Alpha One Generation II and Bravo series sterndrive transom assemblies. Once installed and bent, it prevents the related pivot hardware from backing out under steering load and engine vibration.

Cotter pins are single-use fasteners. They deform during installation and cannot be straightened and reused without losing their locking effectiveness. A new pin should be installed any time the related hardware is disturbed — this is a safety-critical retainer in the sterndrive steering and pivot system.

Part Information

• Part Number: 18-54929
• Short Reference: 54929
• Brand: Mercury / Quicksilver
• Official Product Type: Cotter Pin (Split Pin Retainer)
• Barcode / UPC: 745061159587
• Supersedes: 18-34212, 34212, 34159, 24552, 49324
• Approximate Dimensions: 3.00" L × 0.50" W × 0.25" H
• Approximate Weight: 0.01 kg

Compatible Applications

• MerCruiser Alpha One Generation II sterndrive – gimbal ring and lower swivel pin locations
• MerCruiser Bravo I sterndrive – gimbal ring and hinge pin locations
• MerCruiser Bravo II sterndrive – gimbal ring and hinge pin locations
• MerCruiser Bravo III sterndrive – gimbal ring and hinge pin locations
• Any MerCruiser transom assembly where the parts diagram specifies 18-54929 or a superseded reference (18-34212, 34159, 24552, 49324) at the gimbal ring or swivel pin location

Fitment Note: Verify by drive or transom serial number and the Mercury parts diagram before ordering. Cotter pin size and location can vary by drive generation, gimbal housing design, swivel shaft hardware, and production range.

System & Diagram Position

This cotter pin is part of the transom assembly / sterndrive pivot and steering system. In the Mercury parts diagram it appears in the transom assembly section at the gimbal ring pin, lower swivel pin, and hinge pin locations — wherever a split pin retainer is shown securing a pivot bolt or shaft. It is the final locking element in the hardware stack at those locations, installed after the pin or bolt is fully seated.

Dimensions

• Approximate Length: 3.00"
• Approximate Width: 0.50"
• Approximate Height: 0.25"
• Type: Split cotter pin (single-use)

When to Replace

• Any time the cotter pin is removed from its location — it is a single-use fastener
• Pin is bent, corroded, cracked, or missing
• During any gimbal ring removal, lower swivel pin service, or transom assembly disassembly
• During bellows replacement or transom reseal when the gimbal ring is disturbed

Service Interval

Cotter pins at gimbal ring and swivel pin locations should be inspected during annual sterndrive service and replaced any time the related hardware is removed. They are a standard replacement item during bellows service, transom reseal, and gimbal ring removal.

Installation Notes

• Install a new cotter pin — never reuse a previously bent pin
• Ensure the related pivot pin or bolt is fully seated and at the correct torque before installing the cotter pin
• Insert the pin through the hole in the shaft or bolt, then bend the legs securely in opposite directions per the Mercury service procedure
• Legs should be bent enough to prevent the pin from backing out, but not so sharply that the pin body is stressed or cracked
• Inspect the installation visually before returning the drive to service

Related Parts

• Mercury MerCruiser Gimbal Bearing Kit 879194A02 – Alpha One Sterndrive
• Mercury MerCruiser Gimbal Bearing Kit 879194A01 – Alpha One Sterndrive
• Mercury MerCruiser Gimbal Housing Bushing Kit 805041A2
• Mercury Quicksilver Gimbal Housing Lock Nut 11-34087
• Mercury MerCruiser Quicksilver Gimbal Housing Washer 21900

Technical FAQ

Q: Can I reuse this cotter pin after removing the gimbal ring?
A: No. Cotter pins are single-use fasteners. Once bent, the metal is work-hardened at the bend point and will not return to its original geometry. A reused pin may not seat correctly or provide adequate retention. Always install a new pin.

Q: What superseded part numbers does 18-54929 replace?
A: This part replaces 18-34212, 34212, 34159, 24552, and 49324. If you have an older parts list showing any of these numbers, 18-54929 is the current OEM replacement.

Q: How many cotter pins does my transom assembly require?
A: The quantity varies by drive model and the number of pivot pin locations in your specific transom assembly. Check the Mercury parts diagram for your drive serial number to confirm the total quantity needed before ordering.

Q: Is this pin used on both Alpha One Gen II and Bravo drives?
A: Yes — this part number appears across Alpha One Gen II and Bravo I/II/III transom assemblies, but always verify against the diagram for your specific drive serial number before ordering.

Parts Desk Insights

Best use case: This cotter pin is the right part for any gimbal ring removal, lower swivel pin service, or transom disassembly on a compatible MerCruiser sterndrive. At this price, order a few extras before starting a transom job — they are easy to lose during disassembly and you will need a fresh one for every pin location that is disturbed.

Common issues: The most common issue is reusing the old pin after reassembly. A previously bent cotter pin looks usable but no longer provides reliable retention — in a steering and pivot application, that is a safety concern. A second common issue is ordering only one when the transom assembly has multiple pin locations — check the diagram for your drive before ordering to confirm the full quantity needed at each location.