Abstract: Apparatus for providing a sight glass in the lower gearcase of a marine engine wherein the gearcase has a circular opening in its side. The circular opening has three concentric segments, the outermost segment has the largest diameter and is internally threaded. The center segment is sized to accomodate a disc-shaped transparent sight glass. The innermost segment has a diameter less than the center segment and the surface between the center and innermost segments contains an annular groove. An O-ring or resilient waterproof material fits into the annular groove and the disc-shaped sight glass is fitted into the center segment of the opening in the grearcase with its outer edge pressed against the O-ring. A ring-shaped window cover is then threadedly fitted into the outermost segment of the opening in the gearcase and firmly pressed against the sight glass and locked in place by a lock nut screwed into a threaded hole in the adjoining edges of the window cover and the gearcase.

Abstract: A sight glass assembly for observing the lubricant in the lower gearcase of a marine engine. The assembly is designed to be bonded into a circular hole in the lower gearcase housing and includes a window retaining ring which is bonded to the gearcase housing and a lock ring located inside the gearcase, an annular O-ring of resilient water proof material fitted into an annular groove in the retaining ring, a cylindrical disc-shaped transparent sight glass one of whose two outer edges is pressed against the O-ring, and a window cover having a central void and an annular face which is pressed against the second outer edge of the sight glass. The window cover is threadedly joined to the window retaining ring and is preferably locked into place by a lock screw threaded into a hole in the adjoining edges of the window retaining ring and the window cover.