Operation

The marine transmission is not directly connected to the engine flywheel. A flexible coupling is used from the engine flywheel to the input shaft of the marine transmission. The full power of the engine goes through the marine transmission to the propeller. The propeller turns at a slower rpm than the rpm of the engine flywheel, the coupling and the input shaft of the marine transmission.

The pressure of the oil from the hydraulic pump, on the front of the marine transmission, is used to engage either the astern clutch or the ahead clutch.

SCHEMATIC OF MARINE TRANSMISSION IN NEUTRAL
1. Output shaft. 2. Pinion (from ahead clutch). 3. Pinion (from astern clutch). 4. Gear (for astern clutch). 5. Gear (on output shaft). 6. Gear (for ahead clutch). 7. Gear (on input shaft). 8. Input shaft.

NOTE: The reference to the two clutches in the marine transmission is astern clutch, for output shaft (1) clockwise rotation (reverse) and ahead clutch for output shaft counterclockwise rotation as seen from the stern (back) toward the prow (front) of the vessel.

MARINE TRANSMISSION
1. Output shaft. 8. Input shaft. 9. Control Valve. 10. Hydraulic pump.

When the engine is running and the lever on the control valve for the marine transmission is in the NEUTRAL position, the oil from the hydraulic pump does not go to either the astern or the ahead clutch. With no hydraulic oil in the oil clutches, springs keep the hydraulic oil activated pistons away from the plates and discs and the clutches are not engaged. The engine flywheel turns input shaft (8) and gear (7). Gear (7) turns gear (6), for the ahead clutch, and gear (6) turns gear (4), for the astern clutch. When the clutches are not engaged neither pinions (2) and (3) or gear (5) on output shaft (1) can be turned by the engine flywheel.

MARINE TRANSMISSION CUTAWAY
1. Output shaft. 3. Pinion (from astern clutch). 4. Gear (for astern clutch). 5. Gear (on output shaft). 7. Gear (on input shaft). 8. Input shaft (to coupling on engine flywheel).

SCHEMATIC OF MARINE TRANSMISSION IN REVERSE
1. Output shaft. 2. Pinion (from ahead clutch). 3. Pinion (from astern clutch). 4. Gear (for astern clutch). 5. Gear (on output shaft). 6. Gear (for ahead clutch). 7. Gear (on output shaft). 8. Output shaft.

Move the control valve lever to the ASTERN (reverse) position and pump oil goes from the control valve to the astern clutch. The pump oil, in the astern clutch, engages the clutch. With the astern clutch engaged, gear (4) turns pinion (3). Pinion (3) turns gear (5) on output shaft (1) in a clockwise direction. The output shaft is connected to and turns the propeller to move the vessel in the (astern) reverse direction (when the propeller pitch is for pull with clockwise rotation).

When the astern clutch is engaged, all of the gears in the marine gear turn when the engine is running. Pinion (2) is turned by gear (5), but the pinion turns in a direction opposite to the direction gear (6) is turned.

Move the control valve lever to the AHEAD (forward) position and pump oil goes from the control valve to the ahead clutch. With the ahead clutch engaged, gear (6) turns pinion (2) and pinion (2) turns gear (5) and output shaft (1) in a counterclockwise direction. The output shaft is connected to and turns the propeller to move the vessel ahead (forward) (when the propeller pitch is for push with counterclockwise direction).

SCHEMATIC OF MARINE TRANSMISSION IN AHEAD
1. Output shaft. 2. Pinion (from ahead clutch). 3. Pinion (from astern clutch). 4. Gear (for astern clutch). 5. Gear (on output shaft). 6. Gear (for ahead clutch). 7. Gear (on output shaft). 8. Output shaft.

When the ahead clutch is engaged, pinion (3) is turned by gear (5), but it turns in a direction opposite to the direction gear (4) is turned.

Hydraulic System

The oil for the hydraulic system is also the lubricant for the marine transmission. The oil is in chambers (oil sump) in the bottom of the transmission housing.

The vane-type pump for the oil systems is on the front of the transmission housing. The pump is driven by the gear for the ahead clutch. The pump gets oil from the sump through a strainer and goes out through a line with a shut-off valve. The oil from the pump also goes out through another line to a passage in the transmission housing. The pump oil goes through the passage, through the oil filter and into the control valve for the marine transmission.

MARINE TRANSMISSION
1. Pump. 2. Strainer. 3. Control valve.

The oil filter housing has an oil bypass valve. The difference between the pressure of the oil to the filter element and the oil from the element is the control for the bypass valve. When the difference between the pressure of the inlet and outlet oil is too much, caused by a filter element that is full of dirt, the bypass valve opens. When the bypass valve is open, the pump oil, in the passage in the housing, goes directly to the control valve for the marine transmission.

Two plugs, one in the side of the oil strainer and the other in the right side of the transmission housing and a shut-off valve in the line from the oil strainer to the transmission oil pump are used only if there is an emergency. The oil lines to and from a pump, with a separate drive for the pump, can be connected to where each plug is removed. The valve in the line to the transmission pump is shut-off when the emergency oil pump is in operation.

Control Valve

Neutral Position

The control valve is on the right side of the marine transmission. All of the oil from the pump, when the engine is running, goes into the control valve. The lever on the control valve has three positions which are: AHEAD, (forward), ASTERN (reverse) and NEUTRAL.

CONTROL VALVE IN NEUTRAL POSITION (Engine Running)
1. Control valve body. 2. Control valve spool. 3. Springs (bypass valve). 4. Outlet passage (to oil cooler). 5. Inlet passage (from filter and pump). 6. Bypass valve. 7. Braking (damping) valve.

The NEUTRAL position of the control lever keeps valve spool (2) in a position where the pump oil through inlet passage (5), and a passage in valve body (1), goes to a chamber with no outlet to the clutches. The pump oil also goes through a passage in bypass valve (6) and is stopped by valve (7). With no outlet for the pump oil in the control valve, the pressure of the pump oil increases. Pump oil pressure of 50 to 60 psi (345 to 415 kPa) opens valve (7) and goes into the valve chamber in bypass valve (6). The pump oil in valve (7) chamber has more force than springs (3), in bypass valve (6), and the oil moves the bypass valve. Now the pump oil goes through outlet passage (4), through the oil cooler and through the lubricant passages in the transmission.

AHEAED Position

The AHEAD (forward) position of the control lever keeps valve spool (6), in a position where the pump oil through inlet passage (14), and a passage in valve body (1), goes through passage (13) to the ahead clutch. The pressure of the pump oil must increase to engage the clutch. The pump oil in passage (13) also moves ball (11), goes into check valve (5) and moves the check valve against stop (3). The pump oil in the check valve goes through four orifices (4) and then moves load piston (2). When the load piston moves, it increases the force of springs (10) in bypass valve (16). The pressure of the pump oil through passage (13), to engage the ahead clutch, must increase to 300 psi (2050 kPa) before bypass valve (16) opens. As the pump oil slowly goes through orifices (4), in check valve (5), to move load piston (2), the clutch engages with modulation.

Move the control lever and it moves valve spool (6) to a position in valve body (1), to let the oil from the ahead clutch go from passage (13) through outlet (15) to the transmission case. With no pressure oil in the ahead clutch springs move the clutch piston away from the clutch plates and discs and the clutch is not engaged.

CONTROL VALVE IN AHEAD POSITION
1. Control valve body. 2. Load piston. 3. Stop. 4. Orifices (four). 5. Check valve. 6. Control valve spool. 7. Outlet (for oil to transmission housing). 8. Outlet (for oil to transmission housing). 9. Passage (for astern clutch). 10. Springs (bypass valve). 11. Ball. 12. Outlet passage (to oil cooler). 13. Passage (for ahead clutch). 14. Inlet passage (from filter and pump). 15. Outlet (for oil to transmission housing). 16. Bypass valve.

ASTERN Position

The ASTERN (reverse) position of the control lever keeps valve spool (6) in a position where pump oil through inlet (14), and a passage in valve body (1), goes through passage (9) to the astern clutch. The pressure of the pump oil must increase to engage the clutch. The pump oil in passage (9) moves ball (11), goes into check valve (5) and moves the check valve against stop (3). The pump oil in the check valve goes slowly through orifices (4) and moves load piston (2). The movement of the load piston increases the force of springs (10) in bypass valve (16). The pressure of the pump oil through passage (9), to engage the astern clutch must increase to 300 psi (2050 kPa) before bypass valve (16) opens. The pressure of the pump oil keeps the clutch engaged.

CONTROL VALVE IN ASTERN POSITION
1. Control valve body. 2. Load piston. 3. Stop. 4. Orifices (four). 5. Check valve. 6. Control valve spool. 7. Outlet (for oil to transmission housing). 8. Outlet (for oil to transmission housing). 9. Passage (for astern clutch). 10. Springs (bypass valve). 11. Ball. 12. Outlet passage (to oil cooler). 13. Passage (for ahead clutch). 14. Inlet passage (from filter and pump). 15. Outlet (for oil to transmission housing). 16. Bypass valve.

Clutches

Gear (4), for the ahead clutch, is a left hand gear and the gear like it for the astern clutch is a right hand gear. All of the other parts in the two clutches use parts with the same part numbers.

Long studs in end plate (1) go through drive ring (2) and gear (4). Drive plates and driven discs (3) are the friction parts of the clutch. The six metal plates, each plate between two of the seven lined discs, have teeth that fit into the teeth in the bore of drive ring (2). The lined discs have teeth in the bore that fit on the teeth of shaft (8). The twelve bolts and springs (7) keep piston (5) against gear (4). Nuts on the eight studs from end plate (1) keep the gear and clutch together. Bolts through gear (4) connect the clutch to shaft (9).

When the engine is running, shaft (9) and all of the clutch parts except the seven lined discs turn at one half the rpm of the engine. When the lever for the control valve is moved to the AHEAD (forward) position, pump oil goes through a passage in the center of shaft (9) and through passage (11) into the chamber between piston (5) and gear (4). The pressure of the pump oil in the chamber increases and moves piston (4) against a stationary lined disc. As the piston is moved farther, there is more and more friction until the plates turn the lined discs and shaft (8) at the same rpm as the plates and gear (4).

When shaft (8) turns, the oil from lubricant passage (10) is thrown away from the center and goes through the lubricant passages for plates and discs (3) to cool the clutch.

ONE-HALF OF A CLUTCH (CROSS SECTION)
1. End plate of clutch. 2. Drive ring. 3. Drive plates and driven discs. 4. Gear (for the clutch). 5. Piston. 6. Bearing cap (part of housing). 7. Springs. 8. Shaft (with pinion to drive final gear). 9. Shaft. 10. Passage for lubricant. 11. Passage for pump oil.

Lubrication

The lubricant (oil) for the bearings and gears in the marine transmission is the oil from the pump for the hydraulic system. The oil from the pump goes to the control valve for ahead (forward) and astern (reverse) direction of the vessel and then enough oil goes through the bypass valve in the control valve for the lubrication system of the transmission. An oil cooler with a bypass valve, that is controlled by heat, is in the system between the control valve and the oil manifold in the transmission housing.

The oil to the taper-roller bearings, on the shafts in the transmission, goes through oil passages and lines at approximately 30 psi (205 kPa). The lubrication for the other type roller bearings (five) flows on to the bearings from open oil passages and from oil that runs off the gears as they turn (splash lubrication).

Oil Cooler

OIL COOLER GROUP
1. Line to oil manifold in housing. 2. Electric switch (temperature controlled). 3. Line (from control valve). 4. Valve (thermostat). 5. Line (oil cooler bypass). 6. Oil cooler. 7. Coolant inlet and outlet lines.

The oil cooler group is on the right side of the transmission housing.

When the engine is running, oil from the pump for the transmission, comes from the control valve through line (3). When the temperature of the oil through line (3) is below 155° to 170°F (69° to 77°C), it can not go through oil cooler (6) because valve (4) (thermostat) is closed. The cool oil from the control valve must go through line (5), valve (4) and through line (1) into the oil manifold in the transmission housing. When the temperature of the oil through line (3) is hot, valve (4) thermostat opens and the oil goes through oil cooler (6). The cooled oil from oil cooler (6) goes through open valve (4) and through line (1) into the manifold in the transmission housing.

Electric switch (2) is a normally open (N.O.) switch that closes when the temperature of the oil from the pump through line (3) gets to 210°F (99°C). The closed switch turns ON a warning. The warning is either a horn, a bell or a light.