The Mercury 310 42647A1 Pinion Roller Bearing, also commonly referenced as 42647, is one of the most critical bearings inside a Mercury lower unit, located on the bottom of the driveshaft.
 
Located in the upper gearcase, this precision roller bearing supports the driveshaft directly above the pinion gear and helps maintain proper gear alignment, bearing preload, and gear tooth contact under load.
 
Because every horsepower produced by the engine passes through the pinion gear assembly, the condition of the pinion bearing directly affects gearcase durability, efficiency, and long-term reliability. Whether servicing a fishing motor, bass boat, offshore boat, or Mercury Racing application, this bearing plays a vital role in lower-unit  performance.
 
Why the Pinion Roller Bearing Matters
 
The pinion gear is responsible for transferring power from the driveshaft to the forward and reverse gears. To do this reliably, the pinion gear must remain properly aligned under heavy acceleration, high-speed operation, shifting loads, and propeller thrust forces.
 
A worn, contaminated, or damaged pinion bearing can contribute to improper gear contact patterns, excessive gear wear, vibration, noise, bearing failure, and in severe cases, complete gearcase damage.
 
For this reason, experienced Mercury technicians routinely inspect and often replace the pinion bearing during major lower-unit service or complete gearcase rebuilds.
 
Broad Mercury & Mercury Racing Fitment
 
The Mercury 31 42647 A1 bearing is used across a wide range of Mercury Marine and Mercury Racing lower units found behind many of the company's most popular V6 outboards.
Applications include Mercury 2.0L, 2.4L, 2.5L, 3.0L, and many 3.2L platforms utilizing compatible gearcase designs.
 
Common engines include the XR2, XR4, XR6, XRi EFI, Laser EFI, 150 HP, 175 HP, 200 HP, 220 Laser EFI, 225 HP, 225 Pro Max, 250 EFI, 250XB, 300 Pro Max, 300X, 300XS, and numerous Optimax, Pro XS, and Mercury Racing performance models.
 
The bearing is frequently used in Sportmaster, CLE (Crescent Leading Edge), Fleetmaster, TorqueMaster, and standard Mercury V6 gearcases. It is also commonly encountered during service of Mercury Racing 260 EFI, 280 ROS, 300 Drag, S3000, Formula 1, offshore racing, and lake-race applications.
 
Because Mercury used this bearing across numerous production years and gearcase configurations, serial-number verification is always recommended during parts selection.
 
Critical During Gearcase Rebuilds
 
A proper lower-unit rebuild involves more than replacing seals. Bearing condition directly affects gear life, preload settings, and gear tooth engagement.
 
Since the pinion bearing supports one of the highest-loaded areas inside the gearcase, many builders consider replacement cheap insurance whenever the gearcase is disassembled for gear replacement, driveshaft service, bearing replacement, or complete overhaul work.
 
Replacing worn bearings can help protect expensive gears, propshafts, driveshafts, and internal components while improving long-term reliability.
 
Cross Reference Information
 
This bearing is commonly identified as Mercury 42647A1 and 42647. In some Mercury parts catalogs, it may also appear as 31-42647A1, which designates the complete bearing assembly.
 
These part numbers are commonly used interchangeably when sourcing replacement pinion bearings for compatible Mercury gearcases.
 
The Mercury 42647A1 Pinion Roller Bearing is a small but essential component that helps maintain proper gear alignment and power transfer inside Mercury lower units.
Used in Sportmaster, CLE, Fleetmaster, TorqueMaster, and numerous Mercury Racing gearcases, it remains one of the most important bearings to inspect during any lower-unit rebuild.
 
Whether you're servicing an XR4, Pro Max, 260 EFI, 280 ROS, 300X, 300XS, Optimax, or offshore racing application, replacing worn pinion bearings helps protect valuable drivetrain components and ensures dependable performance on the water.
 
Mercury 42647A1 & 42647 for Sportmaster, CLE, Fleetmaster & Mercury Racing Gearcases