The Mercury Racing Water Jacket Cover, OEM part number 847950-4, is a genuine Mercury / Quicksilver component used on select Mercury Racing 2.4L and 2.5L high-performance two-stroke outboards. This cover is part of the gearcase cooling water passage system used on Sportmaster and 4-Holes CLE (Crescent Leading Edge) lower units.
 
The water jacket cover helps seal the external water passage on the lower unit and supports proper cooling water routing through the gearcase. On high-performance Mercury Racing lower units, proper water sealing is critical because these gearcases are often run at elevated engine heights, high speeds, and demanding load conditions.
 
Designed for Sportmaster and Big Window CLE Gearcases
 
This OEM water jacket cover is commonly used on Mercury Sportmaster and 4-Hole CLE (with the Larger Window measuring 7 3/8" x 2 1/8") gearcases found behind Mercury Racing 2.5L 245 HP Carb, 260 EFI, 260 Offshore, 280 ROS, and 300 Drag outboards, as well as earlier 2.4L Bridgeport and 2.4L Mod-VP applications.
 
Sportmaster and CLE lower units were designed for performance applications where water pickup efficiency, gearcase strength, and high-speed stability are important. Maintaining the water jacket cover and sealing O-ring helps preserve the intended cooling water path through the gearcase.
 
Why the Cover and O-Ring Matter
 
Because the water jacket cover is exposed to water pressure, vibration, corrosion, and repeated gearcase service, the cover and sealing O-ring should be inspected whenever the lower unit is being maintained.
 
A damaged cover, corroded sealing surface, or flattened O-ring can allow water leakage around the jacket area and may reduce cooling system efficiency. In high-performance applications, any cooling water loss or restriction should be addressed before further operation.
 
The correct sealing O-ring for this cover is Mercury OEM part number 25-34776, also referenced as 34776.
 
Service Recommendations
 
Whenever the water jacket cover is removed, the O-ring should be inspected carefully and replaced if it shows signs of flattening, cracking, swelling, cutting, or hardening. Proper sealing surface preparation is also important before reassembly.
 
This is especially important on Sportmaster and CLE gearcases used in racing, offshore, lake-race, or surfacing-propeller applications where cooling water delivery is critical.
 
Correct Mercury Racing Fitment
 
This genuine Mercury / Quicksilver water jacket cover fits select Sportmaster and CLE lower units used with Mercury Racing and High Performance Mercury outboards including the 2.4L Bridgeport, 2.4L Mod-VP, 2.5L 245 Carb, 260 EFI, 260 Offshore, 280 ROS, and 300 Drag race outboards.
 
The Mercury Racing OEM 847950-4 Water Jacket Cover and optional 25-34776 O-ring are small but important service components for maintaining proper water passage sealing on Mercury Sportmaster and CLE gearcases.
 
Whether servicing a Mercury Racing 260 EFI, 280 ROS, 300 Drag, Bridgeport, Mod-VP, or Offshore gearcase, replacing worn covers and O-rings during lower-unit maintenance helps maintain cooling system reliability and long-term gearcase performance.
 
Genuine Mercury / Quicksilver OEM Water Jacket Cover: 847950-4
Optional Genuine Mercury OEM O-Ring: 25-34776 / 34776