Maintaining the integrity of your Mercury outboard’s gearcase is essential. But when the threads where the bearing carrier nut tightens down—also commonly referred to as the retainer nut or cover nut—are damaged beyond basic cleaning, restoring those threads becomes a critical part of a successful rebuild.
 
The Thread Chaser Gear Case Repair Tool from Buckshot Racing #77 is a precision-engineered, heavy-duty solution built specifically for re-cutting and restoring damaged bearing carrier nut threads in Mercury outboard gearcases.
 
This is not just a maintenance tool—it’s a professional-grade instrument for serious marine rebuilders restoring damaged or corroded lower units to like-new condition.
 
Weighing in at 1 lb 11 oz, this robust tool features aggressive cutting teeth and is machined to 4.375"-16 UNC specifications. It perfectly matches the threading used in Mercury’s high-performance bearing carrier assemblies and is effective on 4.375-inch (4 3/8") gear housings that have suffered from wear, cross-threading, saltwater corrosion, or galling.
 
Matches Common Bearing Carrier Nut Thread Specs
 
Our tool is specifically engineered to cut thread profiles that match a wide range of OEM and aftermarket bearing carrier retainer nuts, cover nuts, and locking rings.
 
These include oem and aftermarket part numbers: Sierra 18-3751, 21120, 35912, 445-226, 509035, 52834, 775419, Mercury 79448, 8M0168577, 8M2000347, 8M2011027, 9-72155, CLE 15840, and Sportmaster 158401.
 
Whether you're restoring a corroded thread or cleaning up damaged lower unit threads, this tool ensures compatibility with these critical fasteners, making reassembly safe, secure, and precise.
 
Compatible Mercury Outboard Models
 
The Buckshot Racing #77 thread chaser is compatible with a broad range of Mercury 2.0L, 2.4L, 2.5L, and 3.0L V6 outboards, spanning 135HP to 300HP.
 
Supported models include performance and commercial applications such as the Black Max, XR2, (XR4 and XR6 with Standard size cases), XRi, Pro Max 150HP, 200HP, 225HP, 225X, 300X, and 260 EFI, 280 ROS, and 300 Drag.
 
It also fits popular EFI and carbureted models like the 200 HP, 225 HP, and 250 HP V6 EFI, as well as commercial-grade units like the Marathon, SeaPro, and DTS 6-cylinder outboards.
 
This tool is ideal for restoring threads in Mercury outboards with model designations like V-135, V-150, V-175, V-200, V-225, and V-250, whether EFI or carbureted. It supports builds used in sport, offshore, high-speed, and racing applications.
 
Additional compatible performance models include the 225 Pro XS, Bravo XR One, Bravo XR SportMaster, and Bravo XR Three, often found in tournament and offshore racing setups.
 
It’s equally at home in the shop with sterndrive builds like the Alpha One, R/MR Alpha One, and high-performance Bravo lower units.
 
How to Use the Buckshot Racing #77 Thread Chaser
 
To restore damaged gearcase threads, begin by cleaning the threaded area and applying true "cutting oil".
 
Carefully align the thread chaser tool to the housing, perpendicular to the face. Be careful, go slow, do not cross-thread!
 
Use the Bearing Carrier Retainer Nut Wrench Tool from Buckshot Racing #77 (or equivalent); Turn clockwise to allow the tool’s cutting teeth to engage and re-cut the threads.
 
Work slowly, backing out periodically to clear chips and debris.
 
Once the tool has passed completely through the thread section, clean the area and inspect for smooth, clean threads that are ready to accept the bearing carrier nut, retainer nut, or cover nut.
 
Whether you’re a marine technician, boat racer, or seasoned Mercury rebuilder working on a classic Black Max 2 Liter, a performance 2.4 CLE, Sportmaster 2.5, or a high-output V-200 EFI, the Buckshot Racing #77 Thread Chaser provides the precision, durability, and performance needed to get the job done right.
 
Contact Mike Hill with any questions at +1-714-697-1716 or mike@buckshotracing77.com