Marine drive lower gearcase with efficient lubricant level

1. A marine drive comprising a lower gearcase with a vertical drive shaft driving a horizontal propeller shaft in a torpedo housing having a front and rear and having a propeller mounted on said propeller shaft at the rear of said torpedo housing, said torpedo housing having a top and a bottom and an internal cavity holding lubricant, said lubricant having an upper surface at a given level in said lower gearcase, a vent plug having a discharge condition to discharge lubricant from said internal cavity such that said given level of said lubricant in said lower gearcase is substantially at the top of said torpedo housing, wherein said torpedo housing houses at least one drive gear therein driven by said drive shaft, said lower gearcase has a drive shaft housing portion extending upwardly from the top of said torpedo housing, wherein said discharge of lubricant enabled by said vent plug lowers the level of lubricant in said lower gearcase to be substantially at the top of said torpedo housing and below said drive shaft housing portion, to reduce excessive lubricant churning created by said drive gear churning through lubricant, and concordantly reduce heat, power loss and foaming of lubricant otherwise caused thereby.

2. The marine drive according to claim 1 wherein said vent plug is at the rear of said torpedo housing proximate the top thereof.

3. The marine drive according to claim 2 wherein said torpedo housing has an exterior hydrodynamic surface along which water flows, and said vent plug is mounted to said torpedo housing at a location away from said hydrodynamic surface to prevent cavitation burns.

4. The marine drive according to claim 3 wherein said torpedo housing has an outer perimeter hydrodynamic surface along which water flows rearwardly, and wherein said vent plug is spaced laterally inwardly of said outer perimeter hydrodynamic surface.

5. The marine drive according to claim 4 wherein said vent plug is mounted at the rear of said torpedo housing between said propeller shaft and said outer perimeter hydrodynamic surface, and forward of said propeller.

6. The marine drive according to claim 5 wherein said torpedo housing includes a bearing carrier mounted therein and supporting said propeller shaft for rotation, and said vent plug engages said bearing carrier in threaded relation at the rear thereof.

7. A marine drive comprising a lower gearcase with a vertical drive shaft driving a horizontal propeller shaft in a to torpedo housing having a front and rear and having a propeller mounted on said propeller shaft at the rear of said torpedo housing, said torpedo housing having a top and a bottom and an internal cavity holding lubricant, said lubricant having an upper surface at a given level in said lower gearcase, a vent plug having a discharge condition to discharge lubricant from said internal cavity such that said given level of said lubricant in said lower gearcase is substantially at the top of said torpedo housing, wherein:

said torpedo housing houses at least one drive gear therein driven by said drive shaft;

said lower gearcase has a drive shaft housing portion extending upwardly from the top of said torpedo housing;

said discharge of lubricant enabled by said vent plug lowers the level of lubricant in said gearcase to be substantially at the top of said torpedo housing and below said drive shaft housing portion, to reduce excessive lubricant churning created by said drive gear churning through lubricant, and concordantly reduce heat, power loss and foaming of lubricant otherwise caused thereby;

said vent plug is at the rear of said torpedo housing proximate the top thereof;

said torpedo housing has an outer perimeter hydrodynamic surface along which water flows rearwardly;

said vent plug is mounted to said torpedo housing at a location away from said outer perimeter hydrodynamic surface to prevent cavitation burns;

said vent plug is spaced laterally inwardly of said outer perimeter hydrodynamic surface;

said vent plug is mounted at the rear of said torpedo housing between said propeller shaft and said outer perimeter hydrodynamic surface, and forward of said propeller.

8. A marine drive comprising a lower gearcase with a vertical drive shaft driving a horizontal propeller shaft in a torpedo housing having a front and a rear 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 lubricant having an upper surface at a given level in said lower gearcase, said torpedo housing having an exterior hydrodynamic surface along which water flows, a removable drain plug mounted to said torpedo housing at a location away from said hydrodynamic surface to prevent cavitation burns, removal of said drain plug permitting draining of said lubricant, a vent plug having a discharge condition to discharge lubricant from said internal cavity such that said given level of lubricant in said lower gearcase is substantially at the top of said torpedo housing, said vent plug being located at said torpedo housing, wherein said drain plug and said vent plug are at the rear of said torpedo housing and are distally opposite each other.

9. The marine drive according to claim 8 wherein:

said torpedo housing has a top and a bottom;

said drain plug is proximate the bottom of said torpedo housing; and

said vent plug is proximate the top of said torpedo housing.

10. A method for reducing heat, power loss and foaming of lubricant in a marine drive having a lower gearcase with a vertical drive shaft driving a horizontal propeller shaft in a torpedo housing having a front and a rear and having a propeller mounted on said propeller shaft at the rear of said torpedo housing, said torpedo housing having a top and a bottom and an internal cavity holding lubricant, said lubricant having an upper surface at a given level in said lower gearcase, said lower gearcase having a drive shaft housing portion extending upwardly from the top of said torpedo housing, said method comprising providing a vent plug having a discharge condition to discharge lubricant from said internal cavity such that said given level of lubricant in said lower gearcase is substantially at the top of said torpedo housing, and locating said vent plug at said torpedo housing.

11. The method according to claim 10 comprising locating said vent plug at the rear of said torpedo housing proximate the top thereof to lower the level of lubricant in said gearcase to be substantially at the top of said torpedo housing and below said drive shaft housing portion.

12. The method according to claim 11 wherein said torpedo housing has an exterior hydrodynamic surface along which water flows, and comprising locating said vent plug at the rear of said torpedo housing proximate the top thereof and at a location away from said hydrodynamic surface to prevent cavitation burns.

13. A method for filling a torpedo housing of a marine drive with lubricant, said torpedo housing having a front and a rear, said marine drive having a lower gearcase with a vertical drive shaft driving a horizontal propeller shaft in said torpedo housing and having a propeller mounted on said propeller shaft at the rear of said torpedo housing, said torpedo housing having a top and a bottom and an internal cavity for holding lubricant, said lower gearcase having a drive shaft housing portion extending upwardly from the top of said torpedo housing, said torpedo housing having a drain plug and a vent plug, said method comprising removing both said drain plug and said vent plug leaving respective exposed drain and vent ports in said torpedo housing, introducing lubricant through said drain port into said internal cavity in said torpedo housing and filling said torpedo housing with lubricant until the lubricant flows out of said vent port and without filling said drive shaft housing portion with said lubricant.

14. The method according to claim 13 wherein said drain plug is proximate the bottom of said torpedo housing, and said vent plug is proximate the top of said torpedo housing.

15. The method according to claim 13 wherein said torpedo housing includes a bearing carrier mounted therein and supporting said propeller shaft for rotation, and each of said drain plug and said vent plug engages said bearing carrier in threaded relation at the rear thereof, and comprising removing said drain plug by turning said drain plug out of said threaded engagement with said bearing carrier, and removing said vent plug by turning said vent plug out of said threaded engagement with said bearing carrier.