The upper main bearing in a Mercury 2.0L and 2.5L V6 two-stroke outboard is one of the most important components of the crankshaft support system. It provides stability at the top end of the block, helping to control crankshaft deflection and vibration at high RPM. Without a properly functioning upper main bearing, the crankshaft cannot maintain alignment, and this can quickly lead to premature wear, bearing failure, or catastrophic engine damage.
 
Between 1990 and 2005, Mercury produced a wide range of two-stroke V6 outboards in the 2.0L and 2.5L families, covering horsepower ratings from 105 HP in jet-drive applications up through 240 HP in the SportJet series. The upper main bearing used in these engines, cross-referenced under OEM part numbers 16756, 16756A2, 16756A4, and 16756T8, is a critical service part during any major rebuild.
 
The Buckshot Racing #77 bearing is a direct replacement (for the 16756 OEM part numbers) built to the correct specifications, with an outside diameter of 2.318 inches and an inside diameter of 1-3/8 inches.
 
Fitment Across Model Years
This bearing is found in a broad range of Mercury V6 two-strokes manufactured during the 1990–2005 period. It is used in models such as the 105 and 110 Jet drives, as well as the 115, 135, and 140 HP V6 outboards.
 
It is also standard in the widely popular 150 HP V6 series, including both the Pro XS and Pro Max variants. Higher output models such as the 175 HP V6 and the 200 EFI, Carb, and XRi all share the same bearing specification, as does the 225 Pro Max.
 
Beyond consumer outboards, the same bearing is found in Mercury Racing and High Performance motors, including the SST 120 and S2000 racing engines, and in SportJet configurations ranging from 200 HP to 240 HP.
 
Engineering Considerations
The upper main bearing plays a crucial role in keeping the Mercury crankshaft running true at wide-open throttle. At elevated RPM, the loads on the crankshaft journal are significant, and a worn or inferior 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 high-performance models such as the 150 Pro Max or 200 EFI, which are often run hard and at sustained top-end speeds, the upper main bearing is under constant stress. Choosing a bearing that can withstand these loads ensures smoother operation, reduced wear, and extended engine life.
 
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 is one of the more technical steps in the rebuild process. Many mechanics attempt removal using a heat gun, but a heat gun does not provide enough energy to bring the aluminum cap up to the required temperature.
 
Others try using a propane torch, which produces more heat but applies it in a highly localized way. This risks creating hot spots in the cap, distorting the bore, or even damaging the surrounding surfaces.
 
The recommended procedure is to use controlled oven heating. By placing the top cap in an oven and bringing the temperature evenly to approximately 250–300°F (120–150°C), the aluminum expands in a uniform manner. At this point, the race can be removed smoothly using a proper driver tool or a press, without gouging or stressing the bore. The even expansion is the key to avoiding damage, something that neither a torch nor a heat gun can guarantee.
 
Reinstalling the Race
Installation follows the same thermal principle in reverse. The replacement race should be pre-cooled in a freezer or placed on dry ice, which contracts the metal and reduces its outside diameter. The cap, once again heated in an oven to 250–300°F, expands slightly in diameter. When the chilled race is set into the heated cap with some RED 271 Thread Lock , the interference fit is temporarily relieved, and the race will seat with little resistance.
 
As the two components return to room temperature, the aluminum contracts around the steel race, producing a secure and precise fit. This method ensures that the race sits true and avoids the uneven stresses that can result from forcing a cold race into a cold cap.
 
For Mercury outboards built between 1990 and 2005, the upper main bearing is an essential service part during any crankshaft rebuild or overhaul. Engines such as the 150 Pro Max, 200 EFI, and SportJet 240 rely on this component to keep their crankshafts stable under the heaviest loads.
 
With exact fitment dimensions, compatibility across a wide range of models, and direct replacement for OEM part numbers 16500, 16756A2, 16756A4, and 16756T8, the Buckshot Racing #77 bearing has become a trusted choice among marine technicians.
 
For technical support, contact Mike Hill at +1-714-697-1716 or mike@buckshotracing77.com