The upper main bearing in Mercury 2.0L, 2.4L, and 2.5L V6 two-stroke outboards is one of the most important components of the crankshaft support system. It provides stability at the top end of the block, helping control crankshaft deflection and vibration at high RPM. 
 
This upper main bearing is designed for performance and rebuild applications where accurate crank support is critical. With a race outside diameter of 2.065" and fitment for a 1 1/2" upper crank journal, it matches the specifications required for a wide range of Mercury V6 race and high-performance configurations that call for OEM 16520, 74248, or 74248T.
 
Fitment Across Outboard Models
This bearing is used across many Mercury V6 two-stroke platforms in the 2.0L, 2.4L, and 2.5L families, including high-performance and racing applications. If your engine’s parts list references 16520, 74248, or 74248T, this bearing is the correct upper main service replacement for that configuration.
 
Because high-performance builds and mixed-year powerheads are common in the Mercury world, always confirm part number and journal sizing during teardown—especially when working with modified blocks, aftermarket cranks, or racing midsections.
 
Engineering Considerations
The upper main bearing plays a crucial role in keeping the crankshaft running true at wide-open throttle. At elevated RPM, loads on the upper journal are significant, and a worn or incorrect bearing can allow the shaft to deflect. This leads to increased vibration, uneven oil distribution, and accelerated wear on both the crankshaft and block.
 
In performance and racing models that are run hard and at sustained top-end speed, the upper main bearing is under constant stress. Choosing the right bearing with the correct sizing helps maintain smoother operation, reduces wear, and supports long-term reliability.
 
Removing the Bearing Race
Servicing the upper main bearing requires attention not only to the bearing itself but also to the race that seats in the top cap. This step is one of the more technical parts of a proper rebuild.
A heat gun typically does not provide enough uniform temperature to expand the aluminum cap evenly.
 
A propane torch can add heat quickly but risks localized hot spots that may distort the bore.
A safer method is controlled oven heating. By bringing the cap evenly to approximately 250–300°F (120–150°C), the aluminum expands uniformly. The race can then be removed with a proper driver tool or press without gouging or stressing the bore.
 
Reinstalling the Bearing Race
Installation follows the same thermal principle in reverse. The replacement race can be pre-cooled in a freezer (or with dry ice), while the cap is heated again to 250–300°F. This temporarily reduces the interference fit and allows the race to seat smoothly and squarely.
 
If your build procedure calls for it, apply thread locker per your preferred shop standard or manufacturer guidance. The key goal is a clean, straight, fully seated race with no distortion of the bore.
 
For Mercury 2.0L, 2.4L, and 2.5L V6 two-stroke performance and racing engines, the upper main bearing is a critical service part during any crankshaft rebuild. This bearing is built to match the required dimensions for applications that specify Mercury Racing OEM 16520, 74248, and 74248T, using a 2.065" race OD and fitment for a 1 1/2" upper crank journal.
 
For technical support, contact Mike Hill at +1-714-697-1716 or mike@buckshotracing77.com