The CLE Inspection Window O-Ring Kit, replacing Mercury OEM part number 25-39695, from Buckshot Racing #77 is used to seal the rectangular side inspection access plates found on CLE (Crescent Leading Edge) lower units manufactured between 1985 and 1993.
These side cover plates are installed on both port and starboard sides of the gear housing and are secured using 4 bolts. The covers are removable, allowing for limited inspection and servicing of the gearcase water passage.
The O-ring is installed in a machined groove between the aluminum cover plate and the gear housing casting. Its primary function is to create a watertight seal, maintaining water pressure.
This becomes especially important in high-performance outboard applications, such as those used in Mod VP and offshore hulls, where the lower unit operates under high thermal and mechanical loads and where pressure testing is standard practice during maintenance and setup.
The O-ring is molded from oil- and fuel-resistant nitrile rubber, sized specifically for the recessed sealing channel around the inspection plate. When the cover is torqued to specification, the O-ring is evenly compressed against the machined surface, forming a uniform pressure seal. Two (2) O-rings are required per gearcase, one (1) per side, and are installed identically on both sides of the lower housing.
This O-ring is exclusive to early-model CLE units with small rectangular windows and two-hole water pickups, a configuration that was later discontinued. Mercury CLE units built after 1993 adopted a larger window design, and subsequent lower units—such as the 4-hole CLE, Sportmaster and Torquemaster—either used different sealing methods or omitted the inspection feature entirely.
Installation Notes and Service Guidelines
Proper installation begins with surface preparation. The O-ring groove should be cleaned thoroughly to remove any debris, corrosion, or residual sealant from previous use. The surface of the cover plate and the surrounding area of the gear housing must also be clean and free from pitting. To facilitate installation, a light film of marine-grade grease may be applied to the O-ring to help hold it in place during assembly.
Torque on the cover plate bolts should be applied evenly, using a crisscross pattern to prevent distortion of the plate and to ensure uniform compression of the O-ring. Over-tightening should be avoided, as this can deform the sealing surface or cut into the rubber.
In the Mercury MOD-VP parts catalog (publication #90-813062), the O-ring is listed clearly under the Gear Housing section on page 38, confirming its application for the two-hole CLE configuration.
Includes two (2) CLE Inspection Window O-Rings, replacing Mercury 25-39695
Contact Mike Hill at +1-714-697-1716 or email mike@buckshotracing77.com for technical support.