_INFORMATION SHEET

INFORMATION

A.PURPOSE OF MAIN ENGINE/REDUCTION GEAR MAINTENANCE. The maximum operational reliability and efficiency of an engineering plant requires a planned program of inspections, not only to discover parts that may fail at a critical time, but to eliminate underlying conditions such as misalignment, corrosion, erosion and improper fabrication.

1. RESPONSIBILITY OF THE ENGINEER OFFICER

a. The Engineer Officer's knowledge and supervision directly affects this program of inspections and maintenance. He/she must insure that the proper techniques were used and that the data derived from the inspections are properly interpreted.

b. Engineering maintenance is the coordination of many parts; technical knowledge, i.e. corporate knowledge and technical skills of personnel, (PMS) and of course publications and references.

c. Engineering planned preventive maintenance has been formalized but it must be understood that this program is only the minimum requirement.

d. An Engineer Officer should have an in-depth understanding of the PMS requirements and insure supplemental maintenance is accomplished to insure equipment reliability and safe operation.

e. Training should also be considered as part of a proper engineering maintenance program. The training should not only include proper maintenance procedures but also information that will insure that the equipment is operated under the proper procedures and parameters.

2. TURBINE MAINTENANCE

a. NSTM Chapter 231 Propulsion Turbines is the "bible" for all maintenance actions, inspection procedures and casualty control procedures for main turbines. Taken from the NSTM is a table showing turbine maintenance items and the purpose for each. Periodic tests and inspections have been developed that will insure the items listed are covered (see Figure 1).

MAINTENANCE ITEMS AND PURPOSE TABLE

ITEM	PURPOSE
Verification of radial and axial position of the rotor by appropriate clearance methods	Avoid internal rubs that can make equipment inoperable
A clean lube oil system and the proper lubricant quality and quantity	Avoid wiping of bearings, scoring of journals and thrust collar and chemical attack on those and other critical surfaces
Freedom of turbine controls	Avoid slow action or hag up of throttles
Check condition of oil deflectors and waste oil drains	Avoid ingress of oil into steam system
Check condition of water drains	Avoid ingress of water into lubricating systems, blade erosion and water slugging
Check cleanliness of machinery internals	Avoid ingress of foreign material through access openings or through connected piping, which restricts internal damage (mechanical or chemical)
Check condition of shaft and gland packing	Avoid blowing steam into engineroom or pulling air into turbine or condenser

Figure 1

PERIODIC TESTS AND INSPECTIONS

TESTS/INSPECTIONS	FREQUENCY
Operate LO purifier while underway	Daily
Operate and lubricate all valve operate linkages	Monthly (if secured)
Take micrometer readings on the journal bearings of the main propulsion turbines	Quarterly
Lift sentinel and relief valves by hand	Quarterly (some platforms are semi-annual)
measure main turbine thrust clearance	Annually
Inspect interior of turbine casing	Regular overhaul or if damage is suspected
Clean, inspect, interior of turbine casing	Regular overhaul cycle
Inspect main propulsion bearing journals and oil deflectors measure clearances	Annually and regular overhaul
Inspect shaft packing and journal for condition, check clearances	Regular overhaul cycle
Foundation bolt tightness	Regular overhaul
Drain and refill operating control gear boxes	Annually and regular overhaul
Remove and clean main steam strainer	Regular overhaul
Measure nozzle clearance	Regular overhaul
Test high and low pressure turbine sentinel valves	Annually or regular overhaul

Figure 2

a. The next table (see Figure 2) lists periodic tests and inspections for a turbine. This is a sampling of items and all of these items are covered under the PMS system.

b. Propulsion Turbines are basically designed machines. The dynamic loading and transient conditions applied to main turbines make the inspections and maintenance vital to safe and prolonged operation. The main engine is always in operation while underway, unless a casualty occurs. The only time preventive maintenance can be completed is inport, with the engine secured. Through proper scheduling, a majority of the required maintenance can be accomplished at the same time. This should give the Engineer Officer and MPA a "warm fuzzy", as they will be aware of the exact status of the main engines, including all of the measurements and clearances. This information can be vital to the Engineer Officer if a casualty occurs.

c. The Engineer Officer will find very few actions that ship's force can do to a main turbine. The review of operating logs and the maintenance of clean lube oil are the best things for the turbine. The actual inspection of the turbine internals and casing is performed by the Engineer Officer using the MRC. Prior to the inspection, the Engineer Officer needs to review the MRC and NSTM 231. These documents aid the Engineer Officer in the inspection and assists in the recording of the material history by using standardized terms.

d. During the inspection, the Engineer Officer is only able to see about 10-25% of the HP turbine internals and 40-60% of the LP turbine internals (see Figure 3 as a guide). Access ports allow viewing of the 1st stage area, the exhaust end of the HP and a view of the balance weights. The access ports at the steam inlet or first stage are very small and provide a limited amount of area to be seen. This is due to the casing halves being together and the turbine internals obstructing some of the view. A borescope can be useful in this area, if one is available. The access ports on the LP turbine are considerably larger and provide a more extensive look inside. The major areas that can be observed are the astern elements, the exhaust of the LP and astern elements and the diaphragms and supports.

a. Three things can be useful to the Engineer Officer during a turbine inspection: the use of Morpholine or a corrosion inhibitor when operating; reviewing of the operating logs and knowledge of where damage is most probable. Morpholine or some corrosion inhibitor is carried over in the steam supplied by the boiler. This "coats" the piping and equipment internals. These components become either a light gray or brownish in appearance. The Engineer Officer should be looking for a difference in color. Cracking, erosion or corrosion affect this protective layer and the color will appear different. The Engineer Officer should be keying in on this, as it is hard enough to see the turbine internals. He or she should be aware of this fact and how it will help them. Also, the use of corrosion inhibitors has greatly reduced the problems encountered by corroding materials and this problem is almost non-existent now.

b. The review of operating logs against design limits provided in the main engine technical manuals can help identify possible steam flow problems. Abnormal pressures and temperatures can be used to highlight suspected problem areas. If journal bearing clearances are satisfactory, there should be no problems in the turbine's steam flow. The flow design of the turbine is dependent on the alignment provided by the bearings.

c. The probability of damage or wear is greatest where the highest pressures and temperatures occur. This area is easy to find; the HP first stage and nozzle block (the small access ports allow viewing this area) and the astern elements of the LP turbine (large access ports show this). If there is no damage in these areas, it is a safe bet that the rest of the turbine is okay (as each stage of the turbine there is a pressure drop and temperature is decreased). This area should be of primary interest to the inspector.

d. Important considerations behind the requirements for turbine PMS are maintaining the design steam path clearances and insuring proper axial and radial clearances. As stated earlier, operating logs can be very useful at this point. The two components used to maintain alignment are thrust bearings and journal bearings.

e. Axial clearances are designed to allow for turbine rotor/casing expansion, contraction, and movement. This movement is limited by use of a Kingsbury type thrust bearing on most platforms. Axial clearances can be checked both during operation and when the turbine is idle by using the rotor position indicator. This reading provides a "quick look" or reference of axial alignment.

f. Radial position and alignment of a turbine is maintained by the use of journal bearings. Excessive wear or damage to journal bearings can cause extensive problems inside a turbine, much more than average problems experienced by a damaged thrust bearing. The thrust bearing's maximum clearance is only half the distance between the casing and blading, this allows some safety margin. Once the journal bearing is damaged, the shaft "drops" and rests on the internal components (gland seal and diaphragm labyrinths). This damage affects the seals and steam flow through the turbine. Watchstanders might find this by their hourly readings. If you notice an increase in gland seal steam, blow by of steam from the glands or slightly abnormal bearing temperatures, you should investigate. It is important to realize, that once the internal labyrinths are damaged there is generally little you can do. The ship's force, on most platforms can only change out or repair the outer set of labyrinths, because the turbine casing allows no access to the others. Maintaining the radial position of the turbine and reduction gear components within design limits prevents damage to:

(1) Turbine casing

(2) Turbine blading and shrouding

(3) Turbine diaphragm and packing rings

(4) Turbine oil deflector rings

(5) Reduction gears due to mis-alignment

g.. Propulsion turbines are balanced to a "T" prior to assembly in a ship. As long as all operating parameters are within specifications, the turbine will last for a long time. If something goes wrong with a turbine, sight and hearing will probably be the first indication of something wrong. Your watchstander is the first line of defense. Does he or she know this?

h. The way a turbine is operated can affect the maintenance and reliability of the turbine. A rotor should never sit still for more than 5 minutes after steam has been admitted. If a turbine in operation should suddenly vibrate, the problem could be any one of the following:

(1) Water in the turbine

(2) Bearing failure

(3) Bent or broken propeller blades

(4) Unbalance due to broken or missing rotor blades

(5) Rubbing of blading labyrinth packing or seal rings

(6) Bowed rotor

i. If you hear a rumbling sound and the turbine begins to vibrate, it is probably water or foreign material. But it is important to know that vibrations or noises from either the turbine or shaft can travel to the reduction gears. This greatly affects the watchstanders in their troubleshooting.

j. Sometimes the Engineer Officer might feel an internal inspection is needed if the noises or vibrations were excessive (prolonged operation while bowed or with an excessive vibration can be a contributing factor). A sure sign of something rubbing on the rotor will be a shiny spot on the rotor (that difference in color again). If this is noted during an inspection, immediately investigate the cause and correct it.

k. When rubbing of a turbine blade or labyrinth occurs, the cause will probably be a bowed rotor. Other causes could be:

(1) A defective thrust bearing (usually noticed in an RPI reading)

(2) A wiped journal bearing (possible problems with gland seal steam)

(3) Foreign material inside the casing (Equipment close-out sat?)

(4) Differential in the amount of expansion between the casing and the rotor (proper warm up of the turbines can prevent this)

l. A lot of these problems are preventable by operating safely in accordance with EOSS. The satisfactory operation of a turbine depends largely upon the axial and radial alignment of the rotor in the casing. During normal operations, the temperature of the oil leaving the bearing is the sole criterion available to the operator for judging the conditions of the various bearings. Oil temperature leaving a bearing will vary depending on the changes in speed, especially since all turbine and reduction gears are sliding surface contact bearings. These bearings develop a lot of heat due to friction and are dependent upon proper quantity and quality of the lubricant. Thus, keeping the lube oil quality at it's best is vital to prolonged operation. Over a period of time you should be able to chart the changes and detect any bearing that may be out of specifications (reviewing of operational logs again).

m. If it is suspected that one of the bearings is out of specifications, when the turbine is secured you can take a "quick look" at the bearings. A depth gage is the quickest and easiest means to determine the amount of wear on a journal bearing. When a bearing is first installed, make a measurement on the bearing to act as a base point. Log this reading. This is your reference point. Never make repairs to a bearing solely upon the outcome of a depth gage reading. If a depth gage reading shows up bad, then make other measurements to the bearing before trying to make repairs.

n. If other measurements are required besides a depth gage, then the bearing will need disassembly and inspection. Some journal to bearing rubbing contact is made on each start. A good bearing will show a polished area centered in the lower half of the bearing. Discoloration of bearing surfaces almost always indicate a lubrication problem. Moisture in the oil and operation under high temperatures can produce a tin oxide coating on the bearing. This coating is very hard and builds up to reduce bearing clearance.

o. If a bearing is to be replaced, ensure the spare meets all the design specifications prior to reassembly. When removing an old bearing, do not lift the rotor more than .005 inch. Lifting the rotor too much will damage the shaft packing. The new bearing must be reassembled properly. You can put a bearing in backwards. This could lead to another casualty due to lack of lubrication.

p. The easiest way to measure the axial clearance is by the installed Rotor Position Indicator. Another means would be to position a dial indicator against the rotor and jack the rotor fore and aft three times, using the average of the three. If there is an indication of a worn thrust bearing, then remove the cover to the bearing and make a feeler gage measurement of the bearing. If a bearing needs to be repaired, then repair all surfaces, make new measurements and shim the bearing to ensure it meets all specifications on oil clearances.

q. Most inspections of the turbine internals will be done through access covers. there are two times when you would remove the turbine casing. The first is when there is knowledge or suspicion of internal damage. In this case you should get technical determination of the necessity to disassemble from NAVSEA. NAVSEA will review your operating logs, take their own readings to discover what is going on with the turbine and its' internals. The second time would be three months prior to overhaul and then NAVSEA will again repeat the process to see if lifting the casing is absolutely necessary. Submit a report to the type commander about the condition of the turbine. In both situations the type commander should be aware of the condition of the turbine and will make the final authorization, after he has all the information, to lift the casings. If it is not absolutely necessary, an alternate maintenance action will take place due to the cost of lifting the turbine casing.

r. Whenever there has been a main propulsion turbine opened for repair or inspections, the work is not complete until a dock trial and post repair trial has been satisfactorily completed. The Engineer Officer of each ship will issue instructions for operating the plant during a dock or post repair trial.

s. The trial will go something like this. Install muslin bags in the lube oil strainers and determine the frequency to which these are to be changed. Once the muslin bags are found to be clean, then engage the jacking gear. Station personnel around the turbine to detect any unusual conditions or noises. If none exist, then consider the turbine ready to do a dock trial.

t. For the dock trial the Commanding Officer will determine the maximum number of RPM's he/she wants the shaft to go. The Engineer Officer determines the amount of time needed to warm up the main engines and when ready, notifies the OOD. The bridge determines the number of RPM's and slowly increases to the maximum RPM allowed. If there are no difficulties, then the turbine would be ready for a post repair trial.

B.MEASUREMENT METHODS FOR TURBINE/GEAR BEARINGS

a. Journal bearings can be measured in a few ways. these are the ways available to determine bearing clearances:

(1) The Depth Micrometer Method. This is the quickest method to get an indication of ring wear. These is no disassembly of the bearing. The turbine must be isolated and secured from rotating and the lube oil system must be secured for at least 24 hours prior to taking the measurement. NOTE: This method is only a quick check and should not be used as a final method of determining bearing clearances.

(2) The Bridge Gage Method. This method requires the component to be placed out of commission and disassembled. It is used when there is no access for a micrometer in the bearing. This requires two personnel to perform and is not as accurate. Only a few ships use as the method for taking measurements.

(3) The Crown Thickness Method. This method requires disassembly of the journal bearing. The bearing is rolled out of the component and a micrometer is used to take readings of the bearing thickness at scribed lines on the side of the bearing shell. A drill bit or round object is needed also. The micrometer has a square face and the bearing shell has a rounded shape, the drill bit allows the measurement to take place.

(4) The Leadwire/Plasti-gage Method. This method requires the component to be placed out of commission and disassembled. Leadwire/Plasti-gage method is used primarily on spring bearings which do not have a bridge gage assembly or access hole for a depth micrometer and because of the size and location of the spring bearings.

(5) The OD and ID Method. The bearing is disassembled and the inside of the bearing is measured. The outside of the shaft is measured. The clearance is the difference between the two. This method is very accurate, allowing the bearings wear pattern to be checked. It is recommended to go from a depth micrometer reading to this method as final verification of readings.

b. Thrust Bearings can be measured in few ways. The following methods are available:

(1) Rotor Position Indicator. A "Quick" method for checking rotor position without disassembly. This reading can be taken while the rotor is rotating or idle. The reading gives the relative position of the rotor and is not intended for PMS purposes. Readings are recorded hourly by watchstanders on the main turbines and cold/hot readings of the rotors are recorded during plant start-up.

(2) Thrust Bearing Oil Clearance Method. In this method the turbine must be secured and at ambient temperature. The lube oil system must have been secured for 24 hours, and the thrust bearing has to be intact. The rotor is jacked forward and aft and dial indicator readings are taken. The clearance is the total travel of the rotor.

(3) Taper Gage Method. The turbine must be secured and access to the turbine blading opened. This method is considered accurate but not as good as the oil clearance method due to the experience of the mechanic. The tape gage is inserted between the first stage nozzle and the moving blade. The gage, having been coated with prussian blue, is then taken out and the area with no blueing is read. This is known as the nozzle blade clearance.

(4) Thrust Bearing Inspection. A lengthy method where the thrust bearing is disassembled and visually inspected for wear. This inspection should only be used when one or more of the previously discussed methods indicate excessive thrust clearances.

C.SPECIAL TOOLS FOR INSPECTION AND CLEARANCE MEASUREMENT

a. Outside Micrometer. It is a precision instrument calibrated in .001 inch increments. The outside micrometer is used to measure outside diameters of rod shaped materials or the thickness of flat materials.

b. Depth Micrometer. A precision instrument calibrated in .001 inch increments and is used to measure depth of distance from a pre-described step. This reading usually requires verification from another method.

c. Reading of the Micrometer. The sleeve is marked off in .025 inch increments from 0 to 1 inch. Each numbered mark indicated is .100 inch. The thimble is divided into 25 equal units. One revolution moves the spindle a total of .025 inch.

(1) Steps in reading the micrometer:

(a) Count the "numbered lines showing on the sleeve, and multiply the total by .100 inch.

(b) Count the lines showing between the last "numbered" line and the thimble. Multiply the number of marks by .025 inch and add it to the value obtained in the first step.

(c) On the thimble, locate the line nearest to the horizontal line of the sleeve. Multiply this value by .001 inch and add it to the value obtained in the first two steps.

EXAMPLE

a) 3 x .100 in. = .300 in.

b) 2 x .025 in. = .050 in.

c) 6 x .001 in. = .006 in.

.356 in.

d. Bridge Gage. A precision instrument machined for bearing wear measurement. It is used in conjunction with an inside micrometer, reading a distance form designated landing to journal. Wear of the bearing is the difference between the reading obtained and constant stamped on the bridge.

e. Leads/Plasti-gage. Leads are wire made up of soft un-alloyed lead. It comes in various thicknesses and usually on a roll. This material is being phased out, being replaced by a plastic gage serving the same purpose and easier to interpret when taking measurements.

f. Taper Gage. A taper gage tool is a wedge shaped tool calibrated in .010 inch increments. It is used to measure clearance between blading and casing of turbine.

g. Dial Indicator. This instrument is made up of a calibrated dial (increments of .001) and several components that allow a wide variation in the attachment. This is used to check rotational, vertical and horizontal alignment.

2. BEARING TERMINOLOGY. These terms should be used when recording material history. These are the standardized terms found in the NSTM, use of these makes it easy for future personnel to understand your intent.

a. CONSTANT: A reference, or baseline depth micrometer measurement. A constant is established only upon reassembly after bearing replacement/renewal or disassembly for inspection during which the clearance has been verified to be within design specifications. The constant does not change until the bearing is again disassembled and a new constant is established.

b. CLEARANCE: The difference between the inside diameter of a bearing and the outside diameter of its associated journal. These diameters are initially determined by calculating the averages of four measurements taken on each piece.

(1) Subsequent depth micrometer measurements taken on an in-service bearing will reveal the gradual increase in clearance which occurs as the bearing wears.

(2) Proper clearance is critical to proper lubrication of a bearing.

c. WEAR: The increase in clearance which occurs during the service life of a bearing.

d. SUMMARY: The bearing constant is the reference depth micrometer measurement from the machined boss surface to the top of the journal when the clearance is known to be within design specifications. The constant and the associated clearance must be recorded.

(1) A subsequent depth micrometer measurement taken on an in-service bearing is compared with the constant to determine wear and thus the new clearance. A depth micrometer measurement taken on an in-service bearing will normally be larger than the constant. The difference between these two is the total wear, or increased in clearance, which has occurred since the constant was established. Original clearance plus total wear yields the new clearance, which must be checked against the allowable maximum. Excessive clearance requires bearing work.

(2) A decrease in clearance could be an indication of a wiped bearing, and must be investigated.

3. SETTING ROTOR POSITION INDICATORS. A rotor position indicator (RPI) is used to determine the rotor position in relation to the turbine casing. RPI's are located at the forward ends of the HP and LP turbines. When initial installation of the unit is completed, technical data is supplied which lists specific clearances at blading, casing and unit axial clearances. These readings are used to reset rotor position indicators and are crucial if thrust bearing repair or replacement occur.

a. PROCEDURE FOR SETTING ROTOR POSITION INDICATORS

(1) PERMISSION. Permission to enter turbine bearing housings must be obtained form the Engineer Officer. This authority cannot be delegated. This must be granted if accomplishing thrust bearing clearance PMS or resetting indicators if thrust bearing repair or replacement is needed.

(2) SECURITY. Tag out and de-energize all equipment in accordance with current shipboard instructions. Inventory all tools and equipment before performing maintenance. Thoroughly clean area around bearing housings. Tether and secure all objects, remove all objects from pockets, and jewelry from person. Do no leave open gear case unattended, and maintain security watch in immediate vicinity. A responsible petty officer E-5 or above is required.

(3) INITIAL INDICATOR SETTING/INDICATOR REPLACEMENT (NO CHANGE IN AXIAL POSITION OR THRUST BEARING CLEARANCE). When at ambient temperature, jack the turbine rotor fore and aft three times, measure total axial movement using a dial Indicator. Take the average of three readings to determine rotor thrust, and record. Jack the turbine rotor forward, and zero the rotor position indicator. No further adjustments are needed and the rotor position can be determined directly by pressing the plunger on the indicator.

(4) SETTING INDICATOR IN ACCORDANCE WITH THRUST BEARING REPAIR OR REPLACEMENT. If the thrust bearing measurement is out of clearance, repair or replace in accordance with MRC or applicable technical manual. Measure thrust bearing clearance in accordance with applicable MRC. Remove bearing housing, at ambient temperature jack turbine rotor fore and aft three times. Measuring axial movement using a dial indicator. Take the average of three readings to determine rotor thrust and record. Jack turbine rotor forward and zero rotor position indicator. Thrust bearing total clearance must be known and recorded to again reset indicator or the reading will not be accurate. No further adjustments are needed and rotor position can be determined directly by pressing the plunger on the indicator.

4. FLEXIBLE COUPLING MAINTENANCE AND INSPECTION. Flexible couplings are used to transmit the torque from the propulsion turbines to the reduction gear and allow for small misalignments between the two. Flexible couplings are usually of the Dental or Fine tooth type. Lubricating oil is supplied to the teeth from the adjacent bearing feed line or by separate nozzles.

a. FLEXIBLE COUPLING INSPECTION. Two major areas looked at by the Engineer Officer are the distance piece sliding clearance and the gear teeth backlash. If either of these are unsatisfactory, the transmission of torque or prevention of thrust reaching the reduction gears can be affected.

(1) PERMISSION to enter the reduction gears must be obtained from the Engineer Officer. This authority cannot be delegated.

(2) SECURITY. Tag out and de-energize all equipment in accordance with current shipboard instructions. Inventory all tools and equipment before performing maintenance. Thoroughly clean area around the coupling cover and reduction gears. Tether and secure all objects, remove all objects from pockets, and jewelry from person. Do not leave an open gear case unattended, and maintain security watch in immediate vicinity. A responsible petty officer E-5 or above is the minimum requirement.

(3) REMOVE INTERFERENCE. Remove piping/interference and oil seal/packing rings. Inspect oil seal/packing rings for cuts and tears. Remove the upper coupling cover and aft bearing housing upper half. Rig a lifting strap to support the coupling distance piece.

(4) TO INSPECT COUPLING TEETH, move the coupling shaft (distance piece) forward or aft to permit maximum inspection of coupling teeth. Any tooth damage which impairs sliding requires coupling repair or replacement.

(5) MEASUREMENTS OF COUPLING FLOAT. Clean and ensure the distance piece will slide the full length of travel. Raise the distance piece enough to remove the weight from the coupling sleeves. Move the distance piece hard aft using a rapid motion (a metallic ring should be heard when the distance piece bottoms), then move the distance piece forward. Position the dial indicator against the after surface forward coupling hub; zero the indicator. Slide the distance piece to the extreme aft position, observe and record reading. Repeat the sliding and measurement steps three times and record the average reading. Remove indicator and lower distance piece.

(6) BACKLASH MEASUREMENTS. Install a strap wrench, take up backlash between coupling teeth. Insert thickness gage on opposite side of tooth contact and measure clearance between coupling teeth at 90 degree intervals around coupling. Repeat three times and record readings. Backlash must not be less or greater than design as the gear teeth could be grabbing.

D.MAIN REDUCTION GEAR MAINTENANCE

a. All bearings used in the reduction gears are sliding surface contact journal bearings. This type of bearing generates a lot of heat due to friction. Oil to the reduction gears must be at the proper quality, quantity, temperature and pressure if it is to do its job. Cleanliness of the oil can never be over‑stressed. Lint or dirt, if left in the system, could clog the oil spray nozzles. The lube oil strainers can not trap very fine particles of metal and dirt and these fine particles can become embedded in the bearing metal and cause wear on the bearings and journals. The particles passing through gear teeth act like a lapping compound and removes metal from the teeth. Anytime you find any water in the lube oil system, the cause must be found and corrected immediately. Even a small amount of water can cause pitting and rusting and acidic attack of components.

b. Under normal conditions, a shipyard should handle major repairs and major items of maintenance. Inspections, checks and minor repairs will be handled by ships force. Onboard spares should be enough to replace 50% of the number of reduction gear bearings. Any maintenance or replacing of reduction gear bearings is usually accomplished by a depot level activity due to the availability of tools, training, cost and the intense QA required. Usually bearings are interchangeable between the port and starboard sides. All needed tools and equipment should also be onboard in case of an emergency.

c. Reduction gear journal bearings have what is called a pressure half and non-pressure half. The non-pressure half has a scribe line at one end in the center of the bearings. The pressure half has three scribed lines at one end, one in the center, and one on either side at a 45 degree angle from the middle. The crown thickness of each shell is measured at these scribe marks, usually 1 1/4" from the end. The measurements are taken by the manufacturer during initial alignment. they are stenciled onto the bearings for future alignment checks. Bearing wear can be measured by determining the differences in crown thickness. Bearing wear should never be great enough to allow incorrect gear contact.

d. If at anytime, you have a loss of lube oil casualty and suspect possible bearing damage, inspect the high speed journal bearings first. As these are the bearings that see the fastest speed, if there is damage, it will probably be here.

e. Bearing replacement is a major undertaking, and should never be accomplished without the proper technical manual. As stated earlier, bearing replacement or repair is usually accomplished by a depot, but in an extreme emergency ship's force might be required to perform certain repairs. If a bearing is replaced, ensure that bearings on the end of the gear or pinion do no differ by more than 0.002 inch to maintain shaft parallelism. This involves very precise, controlled actions and tools to complete safely.

f. Once a bearing is replaced, place muslin bags in the lube oil strainers to trap any dirt or foreign matter that is too fine to be stopped by the strainer. Change the muslin bags every 30 minutes until they no longer pick up dirt. At this point you can engage and start the jacking gear.

E.INSPECTION REQUIREMENTS

a. The following inspections of reduction gears shall be made in accordance with the preventive maintenance system:

(1) Weekly circulate lube oil; rotate main reduction gear. This is accomplished when the main propulsion plant has been idle 7 days.

(2) Monthly inspect reduction gear interior. Accomplish this monthly when in idle lay-up after 30 days (yard period/upkeep).

(3) Semi-annually inspect reduction gear spray nozzles, inspect reduction gears. This is also accomplished when inspection of security devices indicates that unauthorized entry may have taken place.

(4) It is highly recommended that the reduction gear be inspected as a part of your relieving POA&M. Both on coming and off going.

F.GEAR NOMENCLATURE. These standard terms should be used in recording material history. These terms are found in NSTM 9420 Reduction Gears.

a. Active profile is the entire loaded side of the tooth as it goes through the gear mesh.

b. Top land - the top of the tooth.

c. Filet is the area from the bottom of the profile to the top of the root land.

d. Sides of gear - the end of the tooth.

e. Root land - the bottom of the tooth.

f. Transverse profile is the actual profile of the tooth as it goes through the gear mesh.

g. Tip round - the beginning of the end round.

h. End round is the area of the tooth from the tip round to the side of the gear.

i. Fillet radius is the concave radius which joins the tooth profile and the bottom of the tooth.

j.. Edge round - the rounded edge of the tooth profile.

G.POINTS OF ATTENTION DURING A REDUCTION GEAR INSPECTION. When inspecting reduction gears, the Engineer Officer should look for the following:

a. Poor tooth contact pattern, heavy contact at one end which tapers off to zero contact at less than 80% of the tooth length. Internal alignment of pinion to gears should be corrected until tooth contact exceeds 80% of length (this is done by a shipyard). Ideal tooth contact is in the middle area of the tooth profile, not at the top or bottom, as this can stress gear teeth and cause damage. The maximum amount of tooth contact is approximately 95%. If tooth contact were 100% the tooth could be stressed at the end round and possibly break.

b. Pitting is the loss of surface material in the shape of small craters, or pits, occurring close to the tooth pitch line, caused by excessive tooth bearing pressure.

c. Dirt tracks are caused by foreign particles passing through the gear mesh, high spots result if the dirt track is prominent. these should be visible at the same spot on all gears where contact occurred.

d. Moderate scoring is the loss of surface material in the shape of radial lines, or scores, occurring above and below the pitch line, caused by excessive bearing pressure and/or marginal lubrication.

e. Severe scoring is the heavy loss of surface material occurring above and below the pitch line with radial score marking, tip will have feather edge, caused by material plastically deformed.

f. Wear may be defined as the removal of metal from gear teeth.

g. Normal wear may be defined as removal of metal from gear teeth at a rate that does not impair satisfactory operation of the gear.

h. Cracked teeth are clearly identified by magnaflux inspection.

i. Tooth fatigue is progressive, a short crack appears and then propagates. Characteristic "Oyster Shell" can usually be seen.

j.. Broken tooth. A section of tooth broken away, if a broken section is at one end and has fatigue, eye fracture may be caused by poor contact or upset tooth. If broken section has no noticeable fatigue eye, break may be due to overload, sudden shock or foreign object passing through mesh, gears with broken teeth should be replaced.

H.GEAR INSPECTION. It is recommended that the Engineer Officer review all documentation (NSTM's, technical manuals and MRC's) before conducting the actual inspection in accordance with the MRC. Prior to opening the gear case the following steps must be performed to ensure a safe and controlled evolution:

a. The Engineer Officer must be contacted for entry and his presence is normally required when the gear case is opened.

b. Secure the area to prevent unauthorized access.

c. Enter in the engineering log the time, date, reason for entry and findings. An entry must be made when the inspection starts and when it is completed. The entry at completion must contain all results of the inspection as an official material history.

d. Clean the area around the inspection ports. This prevents foreign material from inadvertently entering the gear case.

e. Prior to opening the inspection cover, remove personal items from your clothing and person, to include collar devices, pens, jewelry, watches and empty pockets. Tape pockets shut.

f. When using portable illumination devices secure a line to them to prevent their entering the gear assembly in the event they slip from you grip.

g. If the gear must be left open without work in progress, post a responsible petty officer E-5 or above to ensure security.

I.DOCUMENTATION. The remarks "INSPECTION SAT OR UNSAT" entered in the engineering log is unacceptable. It is highly recommended that some type of formal inspection from be developed, or use our sample, so that after the last inspection there is a detailed record of your findings (see Figure 4).

TURBINE PART	LOOK FOR THE FOLLOWING
Interior surface of casing	Corrosion, erosion, condition of casing steam seal surfaces
Nozzle diaphragms	Erosion/corrosion of horizontal parting and vertical steam seal surfaces, condition of radial/axial crush pins. Erosion/corrosion pitting and cracking of vanes
Diaphragm and gland packing rings (carbon and labyrinths)	Wear, freedom of movement, condition of springs, position relative to the rotor
Rotor blading and shrouding	Cracks, dents, tears, erosion, corrosion, lifting of the shroud, integrity of stellite shields, axial and radial rubs
Rotor	Surface cracks of chromed or spray metalled areas. Balance weights intact and firmly anchored. Erosion/corrosion of packing areas and integrity of end plugs on hollow rotors. Journal condition (scoring, wear, pitting) Thrust collar (scoring, wear, pitting, tightness)
Journal Bearing	Wear, loose babbitt, contact pattern, scoring, tin oxide, RTE intact
Thrust Bearing	Shoe wear, loose babbitt, contact pattern, scoring, wear of leveling plate supports, RTE intact
Blading radial seals	Wear, pieces broken out, firmly seated
Horizontal joint (main and nozzle chest)	Steam cutting, evidence of leaks
Casing structure	Cracks in casing, particularly in the HP first stage shell area and floor of main steam chest. Cracks in casing support plates, welds, flex, plates. Proper clearance for and freedom of keys and sliding feet. Distortion of gland housing.
Valves (nozzle, bypass transfer, extraction and drain)	Scoring of lift rods in way of bushings. Condition of stems that may indicate leakage or hang up. Wear of linkages, bearings and cams
Rotor position differential expansion indicators	Wear, adjustment, calibration
Nozzle blocks	Cracks in ligaments between reamed nozzles. Both retainer plates out of position. Loose or broken bolts

NOMENCLATURE OF GEAR TOOTH	PERCENT AND INCHES OF WEAR		CHANGES SINCE LAST INSPECTION *NOTE RUST IF APP.
2ND REDUCTION GEAR
	FWD HELICAL	AFT HELICAL	COMMENTS
2ND REDUCTION GEAR PINION: (UPPER)
ACTIVE PROFILE TOP LAND FILLET SIDES OF GEAR ROOT LAND TRANSVERSE PRO. NORMAL SECTION TIP ROUND END ROUND FILLET RADIUS EDGE ROUND	% IN % IN % IN % IN % IN % IN % IN % IN % IN % IN % IN	% IN % IN % IN % IN % IN % IN % IN % IN % IN % IN % IN

2ND REDUCTION GEAR PINION: (LOWER)
ACTIVE PROFILE TOP LAND FILLET SIDES OF GEAR ROOT LAND TRANSVERSE PRO. NORMAL SECTION TIP ROUND END ROUND FILLET RADIUS EDGE ROUND	% IN % IN % IN % IN % IN % IN % IN % IN % IN % IN % IN	% IN % IN % IN % IN % IN % IN % IN % IN % IN % IN % IN
SPRAY NOZZLES STAR. SIDE 1. 2. 3. 4.	% SAT/UNSAT % SAT/UNSAT % SAT/UNSAT % SAT/UNSAT
SPRAY NOZZLES PORT. SIDE 1. 2. 3. 4.	% SAT/UNSAT % SAT/UNSAT % SAT/UNSAT % SAT/UNSAT