Transmits power from the driving unit to the driven unit.
A MARINE PROPULSION UNIT
Terms used to describe gear type mechanisms.
Speed Ratio and Gear Ratio
_____ are determined by dividing the number of teeth on the driven gear by the number of teeth on the driving gear.
Ratios
Force that causes a rotational movement of a object.
Torque
The ____ of an engine supplies the rotation to the gears and shafts that transmit power to the driven unit.
crankshaft
What increases and decreases torque?
GEARS, the higher the gears ratio, the greater the torque difference
A drive mechanism that changes speed and torque and is common in marine engine installations.
INDIRECT DRIVE
______ are commonly used where engines furnish power for auxiliaries.
DIRECT DRIVES
MECHANICAL DRIVES affect the driven unit by:
- Reducing shaft speed
- Reversing the direction of shaft rotation
- Permitting quick-disconnect of the driving unit
_____ operate most efficiently in a relatively low RPM range.
Propellers
Designs for efficient diesel engines operate at a relatively _____ rpm range.
High rpm range
In order to reduce speed of engine shaft to the propeller, many drive mechanisms consist of:
- REDUCTION GEAR
- REVERSE GEAR
- CLUTCH
- TRANSMISSION
Allows both the engine and propeller to operate efficiently and used to obtain low propeller shaft speed with a high engine speed.
REDUCTION GEAR
Most commonly used method for backing down power; accomplished by reversing the direction of the propeller shaft rotation.
REVERSE GEAR
Used in mechanical drives to disconnect the engine from the propeller shaft.
CLUTCH
Arrangement of the drive mechanism components.
TRANSMISSION
The reduction gear consist of three major subassemblies:
- Forward clutch group
- Reverse clutch group
- Output shaft group
- Externally mounted valve selector
- Five spur tooth gears and pinions
- 10 gpm oil pump
- Drive spider group
- Oil strainer
- Oil breather assembly
- Oil gauge
- Gear pan
- Instruction plate
Components found on a reduction gear
Two gears with identical ratios mounted on the right or left hand side rotation engines with one gear forward and the other gear in reverse to obtain opposite rotation of propellers.
TWINNING
The Twin Disc is completely hydraulic; all bearings are oil lubricated, both clutches rae engaged by high-pressure oil and both clutches are cooled and lubricated by low pressure oil. A mechanical lockup or _____ is provided for clutch engagement in the event emergency perations are necessary.
COME-HOME FEATURE
The MANIFOLD is a multipurpose component that provides a mounting surface for:
- SELECTOR VALVE
- OIL PUMP
- TROLLING VALVE ASSEMBLIES
- PROTECTIVE COVER FOR CLUTCHES
- COME-HOME ACCESS PIPE PLUGS
- OIL RETURN PIPE ASSEMBLY
The ____ group has a short, rigid shaft straddle-mounted on antifriction bearings.
OUTPUT SHAFT GROUP
Connecting output member of the reduction gear.
OUTPUT FLANGE
Two ____ are installed on the bearing retainer and seal around the flange hub.
OUTPUT FLANGE OIL SEALS
Spur-tooth gear that meshes with both the forward and reverse pinions.
OUTPUT SHAFT GEAR
The largest bearing in the reduction gear.
TAPERED ROLLER BEARING
- FORWARD PINION
- FORWARD PINION ROLLER BEARING
- CLUTCH SPIDER
- CLUTCH SPIDER BALL BEARING
- FORWARD CLUTCH SHAFT
- CLUTCH PLATES
- CLUTCH PISTON
- PISTON CARRIER
- HUB AND BACK PLATE
- REVERSE DRIVING GEAR ROLLER BEARING
- REVERSE DRIVING GEAR
Parts that make up the forward clutch assembly
Gear and sleeve that fits around the forward/reverse clutch shaft but doesn’t make contact with the shaft.
FORWARD PINION
Internal gear teeth that mesh with the sintered-metal clutch plates.
CLUTCH SPIDER
Installed on the hub of the CLUTCH SPIDER.
CLUTCH SPIDER BALL BEARING
Input end is spline-connected to the spider. The reverse driving gear is keyed to a tapered area of the shaft is at this end.
FORWARD CLUTCH SHAFT
Mounted on the manifold end of the forward clutch shaft and held in position by the lock plate.
FORWARD CLUTCH SHAFT BALL BEARING
Seven steel clutch plates with internal gear teeth are the driving plates of the clutch.
CLUTCH PLATES
Mounted on the piston carrier and installed so the piston is in direct contact with the clutch plates.
CLUTCH PISTON
The stationary member of the clutch and installed ion the forward/reverse clutch shaft.
PISTON CARRIER
Keyed in position on a tapered area of the forward/reverse clutch shaft.
HUD AND BACK PLATE
Installed on the reverse driving gear for the FORWARD CLUTCH ASSEMBLY or the reverse driven gear for the REVERSE CLUTCH ASSEMBLY.
REVERSING DRIVING GEAR ROLLER BEARING
Keyed to a taper on the forward/reverse clutch shaft.
REVERSE DRIVING GEAR
- REVERSE PINION
- REVERSE PINION ROLLER BEARING
- CLUTCH SPIDER
- CLUTCH SPIDER BALL BEARING
- REVERSE CLUTCH SHAFT BALL BEARING
- CLUTCH PLATES
- CLUCTH PISTON
- PISTON CARRIER
- HUB AND BACK PLATE
- REVERSE DRIVEN GEAR
Parts that make up the REVERSE CLUTCH ASSEMBLY
Mounted on the manifold end of the REVERSE CLUTCH SHAFT and held in position by the shroud nut.
REVERSE CLUTCH SHAFT BALL BEARING
Input end is tapered and keyed to the reverse driven gear.
RESERVE CLUTCH SHAFT
- SELECTOR VALVE BODY
- SELECTOR VALVE STEM
- SELECTOR VALVE BALL BEARING
- O-RING SEAL
- SELECTOR VALVE LEVER
- PRESSURE REGULATOR PISTON
- PRESSURE RATE CONTROL PISTON
- PISTON SPRINGS
- ORIFICE PLATE
- STEEL BALL AND SPRING
- INDEXING DETENT
SELECTOR VALVE ASSEMBLY
High-quality casting that contains four drilled holes for installation on the manifold.
SELECTOR VALVE BODY
Designed with channels and ports that alignwith siimilar ones in the SELECTOR VALVE BODY.
SELECTOR VALVE STEM
Installed on the SELECTOR VALVE STEM.
SELECTOR VALVE STEM BALL BEARING
Installed on the SELECTOR VALVE STEM, between the SELECTOR VALVE STEM BALL BEARING and the SELECTOR VALVE STEM cover. The seal prevents leakage from the SELECTOR VALVE.
O-RING SEAL
It may be operated manually at the reduction gear location or from a remote location by the installation of linkage.
SELECTOR VALVE LEVER
- Largest hole - Entry port for pressurized oil to the pressure rate control piston.
- Meduim hole - Seat for the steel ball in the valve.
- Smallest hole - Orifice for metering pressurized oil to the piston.
THREE HOLES OF THE ORIFICE PLATE
Contains passages and ports for the transmission and direction of pressurized oil within the hydraulic system.
SELECTOR VALVE ASSEMBLY
Its function is to reduce the propeller rpm while permitting the high engine rpm require for operation of engine accessaries.
TROLLING VALVE ASSEMBLY
- Trolling valve body assembly
- Trolling valve stem
- Trolling valve piston and spring
- Trolling valve lever
- Oil seals
- Detent
TROLLING VALVE ASSEMBLY PARTS
A rotary gear type unit mounted on the manifold and driven by by splined drive sleeve on the reverse clutch shaft. The shaft rotates at all times at engine speed and anti-engine direction.
OIL PUMP ASSEMBLY
Maintains the oil in the sump of the reduction gear at the proper temperature.
HEAT EXCHANGER or MARINE GEAR COOLER
What happens if there is to little oil in the reduction gear?
Bearings run hot
What happens if there is to much oil in the reduction gear?
Excessive pressure causes leak at oil seals
What happens if oil is too cold in the Red Gear?
Results in insufficient oil flow
What happens if oil is too hot in the Red Gear?
Some lubricating capacity is lost.
Abnormal noises and vibrations must be _____.
investigated and corrected immediately
What engine oil is recommended to use in reduction gears?
SAE-API service class CD engine oil which is certified to pass TO-2 or C-3 test specifications
Another approved oil for reduction gears is _____.
CC engine oil and MIL-L2104B
DO NOT use ______ multiviscosity oils in twin disc transmissions.
10W-40 etc….
What must happen if there is too much oil in the sump?
Engines must be slowed or stopped until excess oil is removed and normal condition restored.
When should the reduction gear be overhauled?
At the same time the engine is overhauled
How often should you conduct an oil and strainer change on a reduction gear.
Every 1000 hrs
How often should you check the oil level of a reduction gear?
Daily with an oil gauge
How often should you remove OIL BREATHER ASSEMBLY and flush with clean diesel fuel?
Every 500 hrs and with oil changes
Maintenance of gears and bearings requires the lubricating oil to be clean and free of:
- WATER
- METAL
- DIRT
Under normal operating conditions, lubricating oil strainers perform satisfactorily. However, they cannot trap particles of metal and dirt that are fine enough to pass through the mesh. Once through the mesh, these particles may:
- Become imbedded in the bearing metal
- Cause wear on the bearings and journal
- Remove metal from teeth
What must happen at the first sign of emulsion?
Stop the plant and change the oil
The following is a list of periodic inspections that should be performed:
- Reduction gear mounting parts
- Heat exchanger connecting lines
- Rubber blocks
- Pressure gauge assembly
- Zinc electrodes
CAUSES OF LOW OIL PRESSURE
Partially clogged oil strainer
Remedy: Remove and clean oil strainer
CAUSES OF LOW OIL PRESSURE
Stuck pressure regulation piston in selector valve assembly
Remedy: Remove selector valve assembly, then disassemble the valve and clean the piston
CAUSES OF LOW OIL PRESSURE
Broken piston rings in clutches
Remedy: Remove the manifold and disassemble the clutch. Replace the broken piston
CAUSES OF LOW OIL PRESSURE
Come-home setscrew loose or missing
Remedy: Remove the come-home access pipe plugs and tighten loose setscrew by turning countwise or replace missing setscrew.
CAUSES OF LOW OIL PRESSURE
Damaged or worn oil pump.
Remedy: Replace damaged or worn oil pump assembly
CAUSES OF LOW OIL PRESSURE
Incorrect linkage installed on selector valve assembly
Remedy: Adjust the linkage so that the selector valve stem is indexed properly by detent
CAUSES OF LOW OIL PRESSURE
Clogged or plugged orifice in orifice plate of selector valve assembly.
Remedy: Remove the four hex screws that secure the orifice plate cover,plate cover gasket, the orifice plate and the orifice gasket to the selector valve body.
CAUSES OF NO OIL PRESSURE
Low oil level or empty sump.
Remedy: Check for leakage and repair, then refill with oil
CAUSES OF NO OIL PRESSURE
Fully clogged oil strainer.
Remove and clean oil strainer
CAUSES OF NO OIL PRESSURE
Damaged or worn oil pump assembly.
Remedy: Replace damaged or worn oil pump assembly
Steel ball in selector valve not seated properly
CAUSE OF HARSH ENGAGEMENT
CAUSES OF HIGH OIL PRESSURE
Stuck pressure regulation piston in selector valve assembly
Remedy: Remove slector valve assmbly , disassemble the valve and clean the psiton
CAUSES OF OVERHEATING
Insufficient heat exchanger capacity
Remedy: Install heat exchanger of sufficient capacity
- insufficient cooling water flow
- clutch slipping
- oil level too high
- improper oil in oil sump
- trolling at too high an engine speed
- clutch plates being warped
CAUSES OF OVERHEATING
- worn splines between reverse driving and driven gears and clutch shafts
- bearing failure
- worn or damaged rubber blocks
CAUSES OF EXCESSIVE NOISE
Clutch plates warped
CAUSE OF NO NUETRAL
The following are potential cause of propulsion gear failure:
- Poor teeth contact
- Inadequate lubrication
- Foreign objects
______ can result from errors in parallelism between the mating gears which may be caused by an incorrectly supported gearcase or a failed bearing.
POOR TEETH CONTACT
Spotting gear teeth is done by coating the teeth with ______ and then jacking the gear in its ahead direction or rotation.
PRUSSIAN BLUE
A satisfactory ____ has been obtained when at least 80% of the axial length of the working surface of each tooth is contact, distributed over approximately 100% of the face width.
Tooth Bearing
INADEQUATE LUBRICATION is a common cause of scoring or wear and may result from the following conditions:
- Low lube oil pressure
- Restrcited or misdirected oil spray
- Water in the gearcase oil
First, a normal operating temperature should be established for a bearing by taking ______.
Periodic Readings
What is the best indicator of bearing health?
The running temperature of the bearing
- Bearing is running hotter or noisier than normal
- Evidence of bearing material in the L/O filter
- Necessary to investigate or correct poor tooth contact
- Refitting bearings cleanliness is essential
- Conducting a gear tooth mesh check
- Fitting a new bearing
Bearing inspections at other than scheduled intervals
These bearings must be completely removed for inspection.
SLEEVE BEARINGS
