The invention relates to marine drive lower gearcases with a vertical drive shaft driving a horizontal propeller shaft in a torpedo housing and having a propeller mounted on the propeller shaft at the rear of the torpedo housing. The invention more particularly relates to an improved location for the drain plug which upon removal permits drainage of the lubricant in the lower gearcase.

A marine drive lower gearcase includes a torpedo housing with an internal cavity holding lubricant for lubricating the gears and bearings in the gearcase. A threaded drain plug is provided in a threaded bore through the torpedo housing near the nose thereof. The bore typically includes a counter- bore to accommodate the enlarged head of a threaded member. The outer lip of the counterbore at the nose of the torpedo housing is on the exterior hydro- dynamic surface of the torpedo shape along which water flows. The outer lip of the bore is a disruption in the hydrodynamic surface and causes cavitation burns on the torpedo housing and the propeller, i.e. blis¬ tered and removed paint on the torpedo housing ex¬ terior surface just aft of the plug hole bore, and pitting of the propeller. A further objection to the noted drain plug hole is the difficulty in machining same because it is difficult to hold a location on the eliptical surface of the torpedo.

The present invention provides a marine drive comprising a lower gearcase with a vertical drive shaft driving a horizontal propeller shaft in

a torpedo housing and having a propeller mounted on said propeller shaft at the rear of said torpedo housing, said torpedo housing having an internal cavity holding lubricant, said torpedo housing having an exterior hydrodynamic surface along which water flows, and a removable drain plug mounted to said torpedo housing removal of said drain plug permitting draining of said lubricant, characterized by said drain plug being located at a location away from said hydrodynamic surface to prevent cavitation burns on ^" said torpedo housing and said propeller otherwise caused by mounting said drain plug at said hydro- dynamic surface.

In the drawings: Figure 1 is a sectional view of a portion of a marine drive lower gearcase and torpedo housing with an internal lubricant containing cavity and drain plug location known in the prior art.

Figure 2 is a sectional view of a marine drive lower gearcase and torpedo housing with drain plug location in accordance with the invention.

Figure 3 is an enlarged view of a portion of Figure 2.

Figure 4 is a sectional view taken along line 4-4 of Figure 3.

Figure 1 shows a prior art marine drive 2 having a lower gearcase 4 with a vertical drive shaft 6 driven by an internal combustion engine (not shown) and driving a horizontal propeller shaft 8 in a torpedo housing 10. Beveled pinion gear 12, splined to the bottom of drive shaft 6, drives driven gear 14, which is splined to propeller shaft 8. Propeller shaft 8 is supported for rotation at its front end by tapered roller bearings

16, and is supported for rotation near its rear end by spool 18 and roller bearings 20. Spool 18 is mounted to the rear of the torpedo housing and retained within the torpedo housing by spool nut 22. Propeller 24 is mounted on propeller shaft 8 at the rear of the torpedo housing. Torpedo housing 10 has an internal cavity 26 holding lubricant for lubricating the gears and bearings. Spool 18 has a rear portion 28 facing propeller 24 rearwardly thereof and supporting propeller shaft 8 for rotation at tapered roller bearings 20. Spool 18 has a forward portion 30 extending forwardly into cavity 26. The spool includes an annular side wall 32 having an inner surface 34 spaced outwardly from propeller shaft 8 by an annular gap 36. Annular gap 36 is part of and communicates with internal cavity 26 to thus provide lubricant to tapered roller bearings 20.

A removable threaded drain plug 38 is provided through the torpedo housing near the nose thereof and slightly offset to the side of lower s eg 40. Drain plug 38 is received in threaded bore 42, and the enlarged head of drain plug 38 is received in counterbore 44. Plug 38 is removed by unscrewing it from the bore. The hole through the torpedo housing sidewall disrupts the exterior hydrodynamic surface 46 of the torpedo housing along which water flows. This in turn causes cavitation burns on the torpedo housing immediately downstream of the drain plug hole, and also ^"" on the propeller. This also contributes to propeller ventilation.

FIGs. 2-4 show a marine drive lower gearcase and drain plug location in accordance with the

invention, and like reference numerals are used from FIG. 1 where appropriate to facilitate clarity. Removable drain plug 50 is provided in the torpedo housing at the rear thereof for draining lubricant upon removal of the plug. The drain plug is mounted at a location away from the exterior hydrodynamic surface of the torpedo housing to prevent cavitation burns on the torpedo housing and the propeller otherwise caused by mounting the drain plug at the hydrodynamic surface as in FIG. 1. The rear portion 28 of spool 18 has a threaded bore 52, FIG. 3, extending forwardly therethrough. Drain plug 50 has a threaded shank portion 54 threaded into bore 52, and an enlarged head portion 56 bearing against O-ring seal 58 in counterbore 60. Inner surface 34 of annular side wall 32 of spool 18 has a groove 62, FIG. 4, therein axially aligned with bore 52. Drain plug 50 is removed rearwardly by unscrewing it from bore 52, permitting drainage of lubricant from cavity 26 through- annular gap 36 and along groove 62 and out through bore 52.

Water flows rearwardly along the outer perimeter hydrodynamic surface 46 of the torpedo housing.. Drain plug 50 is mounted at the rear of the torpedo housing and extends forwardly thereinto. The drain plug and its mounting bore are spaced laterally inwardly of exterior outer perimeter hydrodynamic surface 46 of the torpedo housing, to prevent cavitation burns on the torpedo housing and the propeller, and to aid in eliminating propeller ventilation. Drain plug 50 is laterally between propeller shaft 8 and outer perimeter hydrodynamic surface 46, and is forward of propeller 24.

Drain plug 50 is accessed from the rear. Propller 24 has a hub 24a with an outer perimeter having a laterally outward extent beyond drain plug 50

to cover the latter. In one embodiment, propeller 24 is removed from propeller shaft 8 to provide access to drain plug 50. In another embodiment with a propeller having a hub with through-hub exhaust passages extend¬ ing rearwardly therethrough in an annulus around the propeller shaft, for example as shown in U. S. Patents Nos. 4,178,873 and 3,871,324, drain plug 50 is accessed through one of the exhaust passages. In this latter embodiment, head 56 of drain plug 50 may have to be laterally reduced in size in order to provide clear¬ ance through the exhaust passage through the propeller hub.

It is recognized that various equivalents, alternatives and modifications are possible within the scope of the appended claims.