The lower main ball bearing is one of the most critical rotating components inside a Mercury or OMC outboard motor. It supports the crankshaft at the base of the block, carrying both the vertical load of the piston assembly and the radial forces generated at high speed.
 
Our recommended bearing is manufactured in Japan by Koyo JTEKT, a world leader in precision bearing technology. Built under ISO 9001 and ISO/TS16949 certified systems, each bearing meets exacting Japanese Industrial Standards (JIS) and ABEC classifications, ensuring perfect dimensional accuracy, long fatigue life, and stable performance even at extreme engine speeds.
 
Unlike generic alternatives, the Koyo JTEKT lower main bearing has been validated for use in both stock and high-performance racing motors. With proper lubrication, the oil-fed design is rated for continuous operation over 12,000 RPM, making it well-suited not only for production outboards but also for racing engines such as the Mercury 260 EFI, 280 EFI, 300 Drag, and S3000 Champ. The superior metallurgy and cage design resist thermal growth and distortion, allowing the crankshaft to remain precisely aligned at wide-open throttle.
 
This bearing replaces several OEM part numbers, including the aftermarket 18-1345, 18-1396, Mercury 21623, 330854, 390641, 41421, 67923, 67923T, 9-51204, and OCM 93306-308U0-00, making it a versatile solution for a wide range of Mercury and OMC products. Its fitment stretches across nearly three decades of outboard production, covering engines from the mid-1970s through the early 2000s.
 
In Mercury applications, this bearing is found in the full lineup of 2.0L, 2.4L, 2.5L, and 3.0L V6 outboards. That includes popular fishing and recreational motors such as the V-135, V-150, V-175, V-200, V-220, and V-225, along with heavy-duty workhorse engines like the Marathon, SeaPro, and Offshore series.
 
It is equally at home in the performance range, where models like the XR2, XR4, XR6 Magnum, Pro Max, Laser XRi, and Super Mag pushed Mercury Racing’s technology into the recreational market. At the highest levels of competition, this same bearing design supports the crankshafts of the 245 Carb, 260 EFI, 280 EFI, 300 Drag, SST-120, and S3000 race engines, where engines regularly operate well above 9,000 RPM.
 
Mercury’s larger displacement 3.0L V6 family, including the 200 EFI, 225 Carb, 225 EFI, and 250 EFI, also relies on this same bearing design, further proving its adaptability across both consumer and racing product lines. The engineering consistency ensures that whether used in a fishing boat, offshore application, or tunnel-hull raceboat, the bearing maintains the same level of reliability and smooth rotation.
 
This bearing also crosses over to Johnson and Evinrude V4 and V6 outboards in the 120 to 300 horsepower range. OEM numbers such as 330854, 390641, and 41421 confirm its role as a direct replacement, allowing OMC owners from the late 1970s through the 1990s to benefit from the same Japanese-manufactured precision.
 
The combination of high-speed capability, oil lubrication tolerance, and certified Japanese quality makes this Koyo JTEKT lower main bearing the definitive solution for restoring or upgrading Mercury and OMC outboards. From everyday use to full competition, it delivers the precision, strength, and durability required by engines that must perform under relentless load and extreme RPM.
 
For technical support, contact Mike Hill at +1-714-697-1716 or mike@buckshotracing77.com