Sight glass for observing lubricant in the lower gearcase of marine engines

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.

BACKGROUND AND SUMMARY OF THE INVENTION 
The present invention relates to marine engines having a lower gearcase 
which normally operates partially submerged in water and provides an 
improvement in my invention set forth in my U.S. patent application Ser. 
No. 144,329 now U.S. Pat. No. 4,757,710. 
A major source of trouble occurring with such marine engines is the entry 
of water into the lower gearcase, especially when the engines are operated 
in salt water. Water leaking into the gearcase mixes with the liquid 
lubricant within the gearcase and drastically reduces the lubricant's 
effectiveness. The water also tends to pit the surfaces of the moving 
metal parts of the power train and these effects eventually cause failure 
of the power train and costly repair and replacement of damaged parts. 
Up to now the only way to guard against damages caused by the entry of 
water into the lower gearcase of marine engines has been to periodically 
take the marine engine out of the water, drain the lubricant and thus 
determine whether or not the lubricant has been contaminated with water. 
Such procedure conventionally recommended by the manufacturers of most 
marine engines, is both costly and time consuming. To take a medium sized 
sport fishing boat out of the water and check the condition of its 
outboard marine engine, most marinas charge in excess of $100 plus the 
cost of materials and supplies used. 
My invention provides a sight glass or window in the side of the lower 
gearcase of a marine engine. The presence of even a few cubic centimeters 
of water mixed into the conventional liquid lubricant contained within the 
lower gearcase of a small outboard engine will turn the lubricant from its 
normally dark brown color to a milky-off white. 
Thus by use of my invention the boat's owner or operator can look into the 
sight glass in the side of the gearcase and immediately determine by 
observing the color of the lubricant within the gearcase whether or not 
water has leaked into the lower gearcase. My sight glass permits frequent 
inspection of the interior of the gearcase without cost or removal of the 
boat from the water. It also permits prompt corrective action to be taken 
in the event water has entered the gearcase, thus saving expensive repairs 
or replacement which would have resulted if the water had remained in the 
gearcase for an extended period of time. 
My present invention is especially designed for use by the manufacturers of 
marine engines. I recommend that the lower gearcase housing be cast with a 
circular opening having a thickness about double the usual thickness of 
the housing in the side of the casing. The outer edge of this hole can 
then be machined and threaded to accept the three elements of my sight 
glass assembly. 
My sight glass assembly includes an O-ring, a disc-shaped sight glass and a 
window cover which is threaded to fit into the internally threaded 
circular opening in the gearcase housing. The opening in the gearcase 
housing contains an axially concentric groove into which is fitted the 
O-ring of resilient waterproof material. Then the preferably flat circular 
transparent sight glass is pressed against the O-ring and firmly locked 
into waterproof connection with the O-ring by the window cover which is 
pressed against the outer edge of the sight glass opposite to the outer 
edge of the sight glass which is pressed against the O-ring. 
The window cover is threadedly joined to the gearcase housing and 
preferably locked into place by a lock screw threaded into a hole located 
in the adjoining outer edges of the gearcase housing and the window cover. 
I have found the foregoing sight glass assembly to be absolutely waterproof 
in tests with no leakage of water into the engine's gearcase.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION 
Referring to the attached drawing, FIG. 1 shows a preferred embodiment of 
my sight glass assembly 11 mounted on the side of the lower gearcase 10 of 
an outboard marine engine. 
The component parts of assembly 11 are best shown in FIGS. 2, 3 and 4. 
Gearcase housing 10 is an aluminum casting with wall thickness of 0.15 
inches except for that portion adjacent to the circular opening shown in 
FIG. 2 which has a wall thickness of 0.30 inches. The stepped circular 
hole which has been cast into the gearcase is machined to provide three 
concentric segments. The first stepped segment 10b of the opening has the 
largest diameter preferably about 1.20 inches which is internally 
threaded. The second or central segment has a diameter of about 0.88 
inches and the third segment has a diameter of about 0.50 inches. An 
annular groove 10a having an outer diameter of about 0.87 inches is 
machined into the surface between the second and third segments of the 
opening as best shown in FIG. 2. 
Annular groove 10a is sized to receive an O-ring 16 made of resilient water 
proof material. Then a disc-shaped transparent light glass 14 is inserted 
into the center segment of the opening in gearcase housing 10. Sight glass 
14 has a diameter of about 0.87 inches and a thickness of about 0.18 
inches so that one outer edge of the sight glass can be pressed against 
O-ring 16 positioned within annular groove 10a. 
Ring-shaped window cover 13 has external threads which are designed to 
screw into the internal threads 10b in the opening in gearcase housing as 
best shown in FIG. 2. Window cover 13 has a flat annular inner face which 
is firmly pressed against the outer edge of sight glass 14 as window cover 
13 is screwed into the opening in gearcase housing 10 to provide a 
waterproof seal of sight glass 14 within the gearcase. 
A two-pin wrench is used to firmly position window cover 13 against sight 
glass 14 and to accommodate the two-pin wrench (not shown) two holes 13a 
are bored along a diameter of the outer face of window cover 13 as shown 
in FIG. 3. 
Various means may be employed to lock window cover 13 into place. However, 
in this preferred embodiment a threaded hole is tapped into the adjoining 
edges of gearcase 10 and window cover 13 and a lock screw 17 as best shown 
in FIG. 3 is screwed into the threaded hole to maintain the two elements 
in fixed position. 
The foregoing preferred embodiment of my invention can also be mounted on 
the lower gearcase of an inboard marine engine as well as on an outboard 
engine as shown in the drawings. 
Use of my unique sight glass assembly on a marine engine, whether inboard 
or outboard, will substantially eliminate the damage caused to the marine 
engine by the entry of water into the lower gearcase, will reduce the cost 
of operation of marine engines and increase the enjoyment of owners of 
boats which employ marine engines. 
While I have described and illustrated a preferred embodiment of my sight 
glass assembly and have described various modifications thereof, it should 
be understood that these descriptions are merely illustrative of my 
invention and are not restrictive, since the scope of my invention is 
limited only by the appended claims.