Chapter 11 - Jounals Bearings and Aligment

7/28/2019 Chapter 11 - Jounals Bearings and Aligment

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ubmarine Main Propulsion Diesels - Chapter 11

11

JOURNALS, BEARINGS, AND ALIGNMENT

A. GENERAL

11A1. General. The operator of any piece of

machinery should thoroughly understand the

various adjustments that are necessary for

perfect operation. It is not enough for him toknow merely which valve to open and close

or the position of maneuvering levers in

order to start, stop, and reverse his machine.

He must possess knowledge of the

functioning of each of its systems when he

manipulates this gear. He should be alert to

note the difference between efficient and

poor performance by the sound, smell, and

touch of the machinery. Instruments, such as

gages, thermometers, and tachometers,

however, should be the guides that the

operator uses in detecting the approach of

trouble so as to take corrective measures

before anything serious occurs.

The modern diesel engine demands greater

skill on the part of the designer and builder

than any other kind of engine. Likewise in

its operation it is far from being foolproof

and requires intelligent attention. The

adjustments are precise and to narrow limits.Overhaul and fitting of the pistons, rings,

bearings, valves and fuel pumps are beyond

the capacity of the ordinary machinist and

demand the efforts of a skilled mechanic. If

it is properly adjusted, a diesel engine, once

started, will run until it is stopped. The

extent of its reliability over a long period of

operation depends upon the intelligence and

skill of its operator.

sixty-fourths and thirty-seconds of an inch are

not recognized in diesel engine work; the

increment of measure for everything is

thousandths of an inch.

There should be a regular routine for checking

the different systems of the engine and

performing upkeep functions. At this time all

indications of wear, parts renewed, and

adjustments made should be recorded in a

systematic log book to be used as a history

from which information may be obtained at

future overhaul periods. This is always done

during submarine refit periods and at any othertime when it is found necessary.

11A2. Construction of bearings. The method

used in construction of a bearing depends

upon the type, the bearing metals to be used,

and the type of use required. In the case of

precision type bearings, it is necessary that the

two halves form a true circle when finished.

This requires rather ingenious practice, and

shop procedures will vary.

Other than the shop procedure, there are only a

few items concerning the construction of

bearings that are worthy of mention. The first

of these is the question of oil grooves. Bearing

lubrication in the 2-stroke cycle engine is

more difficult than in the 4-stroke cycle

engine, since in the latter, the point of contact

between bearing and journals of both main and

crankpin journals rotates around the bearing

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Care must be used when operating oil

engines of any make, regardless of whether

the engine is of the 2- or 4-stroke cycle,

vertical or horizontal, air or mechanical

injection. The working principles are the

same, and the same care must be exerted to

have everything properly adjusted before

starting or operating the engine. Otherwise,

there may be trouble. Every bearing should

be adjusted as tightly as possible. This is a

task for the real mechanic and should not be

entrusted to unskilled personnel. The upkeep

of the engine is an important duty, and one

in which the real engineer shows his value. It

should be kept in mind that measurements of

and assists in the distribution of the oil. In the

2-stroke cycle engine, the point of contact

swings back and forth across the lower bearing

shell and hence, in this engine, it is usually

necessary to provide oil grooves on the

unloaded side to carry sufficient oil to the

loaded half of the bearing. Where bronze or

other flat bearings are used as wrist pins,

ample grooving must be provided. Groovesmay be cut axially, circumferentially,

diagonally, or helically across the face of the

bearing, but should never extend to the edge

since this would allow the oil to spill from the

bearing. All grooves should have rounded

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edges, as the sharp edge of a groove has atendency to act as a scraper and may impair

the oil film.

In order that the flow of oil between the

bearing halves may not be restricted,

bearings are beveled for an arc of about 20

degrees at the joints where the bearing

halves come together, except for a narrow

strip at the ends, where the full thickness of

the metal must be retained to prevent the

loss of oil. The spaces formed by beveling

are called oil cellars.

11A3. Bearing loads. The only bearings in a

diesel engine that require careful

consideration due to the heavy loads placed

upon them are the main, crankpin, and wrist

pin bearings. Other bearings are not so

limited in size, and little attention need be

given them in so far as their ability to carry

the load is concerned. The followingdiscussion pertains principally to the above

three heavily loaded bearings that are

usually limited in size by the space

available.

The study of bearing loading brings two

things to mind: 1) the temperature at which

the bearing must operate, and 2) the

maximum pressure per unit area that will be

surfaces may make physical contact andrupture the oil film.

From the above, it is obvious that an oil film

must be maintained at all times in order to

carry the load. This condition is called stable

lubrication. When the oil film is destroyed and

lubrication of the bearing depends entirely

upon the oiliness of the lubricant, we have

what is known as unstable lubrication. This

latter condition exists when the bearing shaft

is running at too low a speed to build up an oil

film or when the bearing is overloaded.

11A4. Bearing metals. Compared with the

journal, the bearing metal should be

sufficiently soft so that any solid matter

passing through in the oil stream will wear the

bearing instead of the journal.

Roller and ball bearings are frequently used in

diesel engines for smaller shafts, such ascamshafts, and in governors, because they

greatly reduce the bearing friction and because

their smaller clearances keep the shaft more

rigid. In at least one opposed piston type of

diesel engine of medium power, ball bearings

are used as main bearings. For wrist pins,

roller bearings of the needle type are used

extensively in other types of large engines.

With these bearings, lubrication is made



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exerted upon the bearing. Too much pressure

will squeeze out the oil film and ruin the

bearing, and too much heat will reduce the

viscosity of the oil until the film can no

longer be maintained. Both of these are

factors of loading, although the latter is a

product of loading and speed of rotation.

In a diesel engine operating at variableloads, the successful bearing design is

generally the result of experimentation

directed toward the discovery of a

satisfactory bearing for all loads. The loads

that a bearing can withstand are based upon

the assumption that the surfaces of the

journal and bearing are smooth and parallel,

that proper clearances are provided, and that

sufficient lubrication is provided. Too much

oil clearance at the ends of a bearing will

cause excessive oil leakage and subsequent

reduction in load-carrying ability. If the

bearing were closed at the ends, the pressure

would be uniform over its entire length, and

much greater loads could be carried. If the

shafting is of in alignment, or vibrates

severely, as when running at a critical speed,

the faces of the journal and bearing will not

be parallel, and the metallic

simpler, and the amount of freedom of motion

and friction is reduced.

Wood is used in the tail shaft bearings of naval

vessels that are submerged in water and

constantly lubricated and cooled. Lignum vitae

is the wood commonly used for this purpose

since it is of a greasy character and extremely

hard and dense. Other types of materials usedfor this purpose include hard rubber strips and

phenolic resinous materials.

Bronze bearings are used where the pressures

are very high such as at the wrist pin. Here the

load on the bearing is the total gas pressure

less the inertia of the piston. In most modern

diesel engines, bronze is used as the bearing

metal for the wrist pin bearing.

There is no material known that is suitable for

all types of bearings. There are four general

types of alloys used today but each has its own

particular uses determined by the maximum

unit pressure and temperature at which the

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bearing will operate, and by the hardness of

the journal.

Bearing metals should be of such

composition that the coefficient of friction is

low. They should be sufficiently hard and

strong to carry the load, but must not be

brittle. If they are too soft, they will wipe or

be pounded out, destroying the clearance and

reducing the bearing area. In grooved

bearings the grooves will become filled with

wiped metal. When this trouble arises the oil

film is squeezed out, the metal is burned,

and failure results.

The four commonly used types of bearing

linings are: high-lead babbitts, tin-base

babbitts, cadmium alloys, and copper-lead

mixtures.

shells are either forged or cast, and the linings

are made of lead-base babbitt metal.

In the naval service the most frequently

encountered bearing metal used in precision

bearings is that known by the trade name of

Satco. The composition of this metal is as

follows:

Percent

Calcium .30- .70

Mercury .40- .90

Tin 1.00-2.00

Aluminum .15- .17

Magnesium 0.00- .05

Lead Remainder



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The backs for bearings are made either of

steel or bronze in the case of the babbitts,

while only steel backs are used for cadmium

alloy and copper-lead bearings. In some

bearings, an intermediate layer of metal is

used between the backs and the bearing

metals.

The hardness of the above bearing metals

naturally varies with the percentage of

alloying employed. In general, however, the

copper-lead and cadmium alloys are the

hardest, while the high-lead and tin-base

babbitts are the softest. The temperature at

which the bearing metals melt is a rough

measure of their degree of hardness, the

softer metals melting at the lower

temperatures. The softness of the bearing

metal is also a measure of the maximum

allowable unit pressure. The harder the

bearing metal, the greater is the load that a

given size bearing will carry without failure.

Where two metallic surfaces are moving in

contact with each other, such as a journal

rotating within a bearing, wear will

inevitably take place. Since it is easier and

cheaper to renew the bearing, the journal

should "be harder than the bearing.Therefore, when using relatively hard

bearing metals, such as cadmium alloy and

copper-lead, it is necessary to use a hard

alloy steel journal or else to harden the

surface of the journal.

The precision type of bearing is rapidly

coming into universal use for crankpin and

main bearings. There is an increasing use of

very thin bearing linings on steel shells. The

11A5. Bearing installation and adjustment.

In order to insure its successful operation, the

bearing must fit the journal perfectly; the

bearing and journal surfaces must be smooth

and parallel, and the bearing clearance must be

correct. Too great a clearance will allow the

oil to spill out at the ends of the bearing, while

too small a clearance will cause the bearing to

run hot. In general, the least clearance that willallow the successful operation of the bearing is

desirable.

In the modern high-speed engine the precision

type of bearing is generally used. No scraping-

in is done, and no shims are used between the

faces of the two halves. The bearing is

accurately machined to the correct diameter

and the only fitting necessary is an occasional

filing down of the faces of the two halves in

order to obtain a close and even fit when the

bearing caps are brought together. In

connection with the fitting of precision type

bearings, too much emphasis cannot be placed

upon the importance of having the backs of the

bearing shells fit evenly against the bearing

support. Recent experience with bearing

failures due to this improper fitting has shown

its importance. The areas not in contact fill

with oil or air, both of which are relatively

poor conductors of heat, and the transfer ofheat from the bearing is reduced, causing the

bearing temperature to increase. In addition, if

an even fit is not obtained, a flexing of the

bearing shell may result, causing the bearing

metal to crack and flake off.

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To assure an even fit the backs of bearings

should be fitted to their supports in the same

manner that the bearings are fitted to the

journal. Since the back usually is made of

steel, it is necessary to file down the high

spots rather than scrape them down as is

possible with softer bearing metals.

11A6. Bearing failures. When an enginebearing fails in service it can generally be

attributed to one or more of the following

causes:

1. Poor operating conditions and improper

maintenance such as:

a. Improper or insufficient lubrication.

b. Insufficient cooling water.

c. Grit or dirt in oil.

d. Water in oil.

e. Bearings out of alignment.

f. Installing the bearing with improper

clearances or uneven bearing surface.

g. Excessive load on the bearing.

2. Faulty design of the bearing or of the

engine itself.

a. Improper dimensions of length and

diameter.

b. Improper bearing material.

c. Improper lubrication. The lubricant, free

from all foreign matter, must be supplied in

ample amounts.

d. Improperly cooled.

e. Improperly grooved.

f. Improperly baffled. Proper baffles must be

the bearing should be examined at once. Also

the lubricating oil gage pressure to the system

and the passage of cooling water through the

oil cooler should be checked. Sometimes the

overheating may be due to foreign matter in

the lubricating oil. The oil should be rubbed

between the fingers to detect the presence of

grit or dirt. An inspection of the filters will

also reveal any abnormal amount of foreignmatter deposited there. Since used oil

generally is slightly acid, the presence of salt

water may be detected by inserting a strip of

red litmus paper in a sample of the oil. If salt

is present to any degree, the litmus paper will

turn blue. If salt water is detected in the oil,

the crankcase and sump tank should be drained

and refilled with new oil after flushing the

system thoroughly. If possible, the cause of

the salt water in the system should be

determined. At the first opportunity the systemshould be well cleaned to remove any particles

of salt that may have been deposited there.

As a rule, hot bearings may be traced to one or

more of the following causes:

1. Improper or insufficient lubrication.

2. Grit or dirt in the oil.

3. Bearings out of line.

4. Bearings set up too tightly.

5. Uneven surface of bearing or journal.

6. Bearing overloaded.

If the temperature of the bearing continues to

rise after the oil supply has been increased, thecondition known as a hot bearing arises. The

danger of a hot bearing lies in the fact that the

babbitt expands until it grips the journal, thus

causing a constant increase in friction and

heat. When the temperature reaches the

melting point of the bearing metal, the metal

will run or wipe.

The treatment of heated bearings involves two



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fitted to prevent loss of oil, or its passage to

adjacent parts of machinery, such as

generator armature, where damage would

result to the commutator. Also in some cases

baffles are used to prevent the mixing of

water with the lubricating oil.

3. The use of inferior lubricants, or the use

of a good lubricant which does not meet therequirements of the piece of machinery.

a. Corrosion of bearings.

4. Inferior workmanship and material in the

manufacture of the bearings and engine

parts.

A bearing that is not operating properly will

overheat. When this occurs, and the reason isnot immediately known, the oil supply to

main items: the removal of the cause, and the

restoration of the bearing to its normal

condition. If the trouble is due to improper or

insufficient lubrication and is discovered

before the metal has wiped, an abundant

supply of oil usually will be sufficient to

control the situation and gradually bring the

bearing back to its normal temperature. Should

the trouble be caused by an accumulation ofdirt on the bearing, the abundant supply of oil

will generally flush out

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the impurities sufficiently to permit

operation.

If the trouble is caused by foreign matter in

the oil, the oil will have to be renovated or

renewed. If the bearings are out of

alignment, if they are set up too tightly, or if

they have been improperly fitted, the fault

cannot be fully remedied until the improper

adjustments have been rectified. This usually

involves stopping the engine.

In all cases the temperature of the bearing

can be lowered by slowing down and thus

decreasing the amount of load on the

bearing. If the trouble has reached an

advanced stage, it may be found necessary tostop the engine. When stopped, the bearing

cap can be eased up a slight amount, thus

increasing the clearance between the bearing

and journal. However, the greatest care must

be exercised in easing up on the bearing cap,

for if too great a clearance is given, trouble

will be experienced from pounding.

When the trouble is inherent in the bearing -

condition can become serious enough to cause

bearing failures, and the only remedy is to

machine or grind down the journal until it is

again cylindrical. This, of course, will reduce

the diameter and necessitate using a bearing of

a different bore in order to effect the proper

bearing clearances.

Journals should be kept smooth, even, and free

of rust at all times. To remove spots of rust or

ridges, the journal should be dressed with a

fine file and then lapped with an oilstone or

with an oilstone powder. Carborundum may

also be used. If Carborundum is used, great

care must be taken to remove all particles, as

these, if allowed to remain, will cause cutting

and grinding of bearings.

When bearings have been removed for long

periods, such as during a major overhaul, it is

customary to wrap the journals with canvas in

order to protect them from accidental damage.

When this is done, only new canvas should be

used. There have been cases where journals

were wrapped with old rags or burlap that

contained some acid. The action of this acid



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as for example, if the machinery is not

properly lined up, or the bearings are of

insufficient area, or not in proper condition-

only temporary relief can be secured from

using the various means suggested above.

The most effective treatment of a hot bearing

is probably the operation of the machinery at

a low or moderate power until such time as

the needed readjustments, changes, orrepairs can be effected.

To summarize the treatment for a hot

bearing, the measures to be taken may be

selected according to the special

circumstances, from the following:

1. Lubrication.

2. Slowing down, and consequent reduction

of load, or stopping.

3. Cooling water to oil cooler.

4. Easing up bearing caps.

Even though relief is obtained by the above

measures, it should be borne in mind that

once a precision bearing has wiped, it is

necessary to renew the bearing as soon as

possible.

The wear on journals rotating in bearings is

seldom, if ever, evenly distributed over the

entire surface. Consequently the journal

wears until it becomes eccentric or egg-

shaped. This

corroded and pitted the journals and it was

found necessary to renew the entire shaft.

Each time a bearing is removed for any reason

the journal should be carefully inspected. Any

evidence of pitting or general corrosion

indicates the presence of acid or water, and the

lubricating oil should be analyzed

immediately. When a bearing clearanceexceeds the allowable tolerance, or when the

bearing fails due to scoring, wiping, spalling,

or cracking, looseness of the bearing metal, or

for any other reason, it must be renewed.

To renew a precision type bearing it is first

necessary to have available a spare bearing.

These are manufactured to size and are

available from the manufacturer. They are

bored to correct dimensions, so that only a

slight amount of scraping in and filing of the

edges of the shell faces is required to produce

an accurate fit. There seems to be a tendency

to renew Satco bearings before it is necessary.

A slight amount of spalling is not necessarily

an indication that the bearing properties of the

metal are destroyed.

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B. COUPLINGS



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11B1. GM elastic coupling. The crankshaft

of the GM 16-278A engine is connected to

the generator shaft by means of an elastic

coupling. The elastic coupling connects the

engine to the generator flexibly by means of

radial spring packs. The power from the

engine is transmitted from the inner ring, or

spring holder of the coupling, through a

number of spring packs to the outer springholder, or driven member. A large driving

disk connects the outer spring holder to

Figure 11-1. Elastic coupling cross section,

GM.

the flange on the driven shaft. The pilot on

the end of the crankshaft fits into a bronze

bushed bearing on the outer driving disk to

center the driven shaft. The turning gear ring

gear is pressed onto the rim of the outer

spring holder.

The inner driving disk through which the

camshaft gear is driven is fastened to the

outer spring holder. A splined ring gear is

bolted to

the inner driving disk. This helical internal

gear fits on the outer part of the crankshaft

gear and forms an elastic drive through the

crankshaft gear which rides on the crankshaft.

The splined ring gear is split and the two parts

bolted together with a spacer block at each

split joint. This makes it possible to engage

separately the two parts of the splined ring

with the crankshaft gear teeth, and to slidethem into position with the idler gear in place.

The parts of the elastic coupling are lubricated

with oil flowing from the bearing bore of the

crankshaft gear through the pilot bearing.

11B2. F-M flexible coupling. The crankshaft

coupling on an F-M installation consists of

three parts: the engine coupling driving half,

the laminated rings, and the generator

coupling driven half. The coupling driving

half is fastened to the lower crankshaft with

fitted bolts, and the coupling driven half is

likewise fastened to the generator shaft. Power

from the engine is transmitted through the

laminated rings by means of a third set of

fitted bolts held in place by ring bolt spacers.

Pilot rings between the ends of the generator

shaft and the crankshaft form a safety guide in

the event of failure of other parts. Tappedholes for jackscrews and drilled holes for body

fitted bolts are provided in the lower flanges of

the cylinder blocks. To permit fitting of the

coupling bolts to the generator shaft, it is

necessary to remove the lower and upper

halves of the end cover back of the coupling

driver half, the lower bearing cap, and the

lower crankcase side cover at the vertical drive

compartment.

Guards and two jackscrews of different

lengths are furnished with the tools by the

engine manufacturer for use in removing and

installing the coupling bolts. The guards

protect the bolt threads and are tapered to

facilitate entry of the bolts when fitting.

When installing coupling bolts in either set,

the shorter jackscrew should be used for



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starting the installation and the longer

jackscrew for completing it.

221

Figure 11-2. Crankshaft coupling, F-M.

C. ALIGNMENT

11C1. General. Good engine and generator

performance can be obtained only if the

original coupling installation is made with

the components in correct alignment andwith correct clearances. The problem of

originally aligning a generator set and

subsequent checking arise quite frequently

during submarine wartime operations. The

original alignment, of course, is extremely

important as it greatly influences future

operation and adjustment of the engine.

During navy yard overhauls it is common

practice to take motors and generators out of

the ship for overhaul, and the young

engineer officer or new leading chief motormachinist's mate is frequently called upon to

check an alignment job being done by naval

shipyard personnel. It as also become routine

to check crankshaft alignment to some

degree after an engine overhaul in which

many of the engine parts have been renewed.

This may be only a checking of the crank

cheek deflections with the use of a strain

gage, but even this will give the operating

good idea as to the status of the alignment of

the equipment. The most important and most

difficult job of alignment is the complete

installation, of a generator set. The salientpoints of these installations will be covered in

the following paragraphs. When the principles

involved in a complete alignment job are

understood, smaller alignment problems

become relatively simple.

NOTE. Alignment tests and corrective

measures should never be undertaken when a

vessel is in drydock because the alignment of

the shafting is not the same when the vessel is

waterborne as when it is in dock.

11C2. Strain gage readings. The strain gage

is basically a micrometer for measuring the

differences in distance between the two webs

or cheeks of a crankshaft during a revolution

of the shaft. As previously stated, one of the

basic alignment procedures is the taking of

strain gage readings. This is a relatively simple



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personnel a

222

Figure 11-3. Position of crankshaft for strain gage readings.

Figure 11-4. Measuring crank check deflection with a strain gage.

223



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undertaking but it is important that the

procedure be followed exactly for best

results. A series of strain gage readings of a

crankshaft gives a measurement of the crank

cheek deflection for various angular

positions of the shaft. The measurement is

accomplished by placing the gage between

the engine crankshaft cheeks. The gage

should be installed with its two endpoints inthe crankshaft prick-punch marks. The

crankshaft should be turned to its initial

position so that the gage will be as close to

the top position as possible without touching

the connecting rod. The dial of the strain

gage is then set on zero, and the crankshaft

is slowly jacked over to subsequent positions

as shown in Figure 11-3 and the readings

taken. When taking the readings, the gage

should not be allowed to rotate about its end-

points.

After the readings have been taken for one

revolution of the crankshaft, they should be

compared, and the maximum crank

deflection obtained. Large variations in the

individual readings indicate some type of

misalignment in the installation.

11C3. Alignment of engine crankshaft

with one bearing generator. This type ofinstallation is that normally found on F-M

generator sets. There are many recognized

methods of accomplishing alignment of

engine and generator. The following

procedure is one method and is discussed

more from the standpoint of alignment

principles than of a standardized alignment

procedure.

Generators and crankshafts that are beingcoupled together must be in alignment. This

condition is attained by moving the shaft

bearing supports vertically and horizontally

until the two halves of the coupling are true

to each other or until the axes of the two

shafts coincide at the point where they are

coupled. The operation usually involves

movement of the entire generator casing.

In the following alignment it is assumed that

Figure 11-5. Using hydraulic jack to adjust

height of generator body for proper verticalalignment.

In all modern submarines the engines are

attached to a generator rather than directly to

propeller shafts. When a generator is being

installed, it should be originally placed as

nearly as possible in final alignment.

Subsequent procedure is as follows:

1. Attach the driven half of the crankshaft

coupling to the driver half by installing the

outer row of bolts around the coupling.

Tighten the bolts evenly.

2. Secure the generator shaft to the flexible

coupling by installing coupling bolts through

the flange on the end of the generator shaft

into the driven flange of the coupling.

3. Check the strain gage measurements to

determine whether or not the couplingoperation has affected the original reading. If a

large change is noted at a particular position of

the crankshft, it indicates that the coupling has

placed a strain on the crankshaft.

4. Check the thickness of the flexible coupling

with a micrometer. The measurements should

be made at the top and bottom, inboard and

outboard. Compare the measurements with



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the engine is already located. Before starting

alignment, the amount of crankshaft cheek

deflection should be known and recorded in

order to be able to make a comparative

check during and after the alignment has

been completed. The crankshaft cheek

deflection readings should agree within

approximately 0.002 inches.

224

Figure 11-6. Using portable block and jack

screw to adjust generator body for proper

lateral alignment.

Figure 11-8. Using portable block and jack

screw to adjust generator for proper thrust

clearance.

Figure 11-7. Measuring generator thrust

bearing clearances.

Figure 11-9. Measuring crankshaft thrust

bearing clearance toward control end of F-M

engine.



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225

the established dimension stamped on the

flange by the manufacturer. For example, the

manufacturer's dimension is 5.225 inches.

The outboard measurement as made with the

micrometer is 5.250 inches. The inboard

measurement is 5.200 inches. This indicatesthat the generator shaft is placing a strain on

the inboard side of the coupling and is

probably also affecting the strain gage

reading on the crankshaft. Therefore, the

generator casing and shaft must be moved

outboard 0.025 inches to balance the

readings on the coupling and to remove the

strain from the crankshaft. Normally, this

should bring the strain gage readings back to

the original readings.

If a difference in the measurement of the

coupling, against the stamped dimension,

occurs at the top or bottom of the coupling,

the generator casing and shaft will

necessarily have to be raised or lowered to

effect a balanced condition. The height of

the generator casing and shaft may be

adjusted by means of hydraulic jacks placed

under the casing as shown in Figure 11-5.

When the proper height is attained, block upthe casing, remove the jacks, and install

shims between the feet and the permanent

pedestals on the deck.

The generator shaft and casing may be

moved inboard or outboard by installing a

portable block and jack screw against the

edge of the side foot mountings of the casing

as shown in Figure 11-6. To check the

distance of the movement, attach a dial

indicator on the opposite pedestal with the

indicator pointer touching the edge of the

opposite foot of the casing.

5. Remove the generator thrust bearing cap

and measure the generator shaft thrust

bearing clearances (Figure 11-7). The

clearances should measure 0.0075 inch

(approximately) at each end and on each side

of the bearing in an F-M installation. If it is

Figure 11-10. Measuring crankshaft thrust

bearing clearance toward generator end of F-

M engine.

and generator thrust bearing clearances.

6. Measure the crankshaft thrust bearing

clearances by inserting a feeler gage between

the crank cheek and the face of the bearing

(Figure 11-9), and between the vertical drive

gear and the generator end of the bearing face

(Figure 11-10). The total clearance should

measure between 0.004 and 0.010 inch evenly

distributed on both sides. If the clearance on

one side is greater than on the other, it will be

necessary to move the generator shaft in one

direction or the other to balance the

measurements.

Any movement of the shaft will affect theclearances at the generator thrust bearing. It

may also affect the strain gage readings and

the setting of the flexible coupling. Additional

movement, therefore, of the shaft, or the

casing may be necessary to bring about a

balanced condition. A check should be made

after every move and steps taken to correct

any offset condition which may have been

brought about by a previous move.



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found, for example, that there is no clearance

at the thrust face away from the engine, the

generator casing must be moved toward the

engine 0.0075 inch with a portable block and

jack screw (Figure 11-8). This operation,

however, should not be accomplished until

the crankshaft thrust bearing clearances have

been measured, since it is possible that only

one movement of the casing will be neededto correct both crankshaft

7. Movement of the generator casing, or

226

the shaft, will probably have some effect on

the generator air gap (the space between the

armature windings and the pole pieces). The

air gap must be uniform around the diameter

of the armature. The clearance should be

kept within the limits specified by the

manufacturer of the generator. Air gapmeasurements are taken with long thickness

gages furnished for this purpose. The gages

are inserted between the armature winding

and each pole. When the air gap is found to

be greater at the top than on the bottom, the

generator casing will have to be lowered by

loosening the jacking screws located on the

side feet of the casing. If the gap is greater at

the bottom, the casing must be raised with

the jacking screws, and shims insertedbetween the side feet and the pedestals.

Assuming that the shaft alignment has been

completed and is true, it will be necessary to

secure the rear foot of the generator casing

to the rear pedestal with a C-clamp. This will

hold the alignment of the shaft while the

casing is moved for adjustment of the air

gap.

After attaining a balanced air gap, correct

shims should be installed. A complete

recheck of all clearances should be made to

verify the alignment installation. This check

must include another set of strain gage

readings. Before this final check, the

generator casing should be rigidly secured in

position with a C-clamp to prevent any

possible movement of the casing.

than on the other, the crankshaft must be

moved in whichever direction will balance the

clearances. This may be accomplished with a

pinch bar placed between the crank cheeks and

the engine framework. After clearances have

been balanced, the crankshaft must be blocked

with hardwood wedges placed between thecrank cheeks and the framework, to prevent

movement of the crankshaft during the

coupling operation.

3. Determine the amount of fore-and-aft

movement of the elastic coupling. This

measurement is made by placing the pointer of

a dial indicator against the face of the outer

driving disk of the coupling. The indicator

may be secured to the upper half of thecoupling housing and the pointer should touch

the driving disk near the center. The coupling

is then forced as far forward or aft as possible,

with a pinch bar, and the dial indicator is set

on zero. Make a prick-punch mark on the face

of the outer spring holder in line with the

jacking gear pointer. Then force the coupling

as far as possible in the opposite direction and

make another mark. The dial indicator reading

denotes the full fore-and-aft movement of the

coupling, which normally is about 0.0125

inch. In order to divide the coupling thrust

evenly between the engine and the generator,

the coupling must now be moved to the center

of its thrust or 0.0625 inch using the dial

indicator as a guide. Make a third prick-punch

mark between the two previously made. This

mark is the reference mark used to check the

center of the coupling thrust after alignment

has been completed.



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11C4. Alignment of engine crankshaft

with two-bearing generator. This type of

installation is typified by the GM generator

set. The GM engine is connected to the

generator by means of an elastic coupling. A

procedure to follow in aligning a generator

to the coupling is as follows:

1. Take strain gage readings to determine theamount of crank cheek deflection. The

maximum permissible deflection in a GM

engine is 0.0035 inch. The measurement

should be re-recorded for reference after

completing the alignment.

2. Check the engine crankshaft thrust

bearing clearances with feeler gages.

Clearance should total approximately 0.030

inch, equally divided on both sides of the

bearing. If the clearance is greater on one

side of the bearing

4. Remove the outer driving disk from the

coupling and bolt it to the flange on the

generator shaft. Check the amount of

deflection of the face of the disk with a dial

indicator by turning the generator armature

one complete revolution. The deflection

should not exceed 0.001 inch. Next, place the

indicator pointer against the rim of the disk,

rotate the shaft one revolution, and check the

amount of deflection. This measurement

should also be within 0.001 inch. If the

amount of deflection, on either the face or the

rim of the disk, is greater than 0.001 inch, the

condition may be corrected by loosening the

bolts and recentering the disk or by cleaning

the inner surfaces of both disks.

227

Figure 11-11. Elastic coupling, outer driving

disk removed, GM.Figure 11-12. Elastic coupling, inner spring

holder removed, GM.



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Figure 11-13. Mastic coupling, outer driving

disk mounted, GM.

Figure 11-14. Elastic coupling, outer driving

disk mounted on generator, GM

228

After obtaining deflection readings within

0.001 inch, the bolts, the driving disk, and

the generator shaft flanges must be marked

so that they may be replaced in their

respective positions when the generator is

coupled to the elastic coupling. Before

removing the flange, the dowel holes must

be reamed for the body-bound dowels.Dowels and dowel holes must also be

marked so that they will be replaced in their

respective positions.

5. Remove the driving disk from the

generator shaft and reinstall it on the elastic

coupling.

6. Install the upper half of the elastic

coupling housing. Move the generatortoward the engine. Approximate axial

alignment may be attained with the jacking

screws on the generator feet. Inboard and

outboard alignment may be attained by use

of portable blocks and jack screws working

against the edges of the generator feet. When

an alignment as nearly perfect as possible

has been attained, the generator is moved

farther toward the engine and the generator

shaft carefully inserted into the bore of the

with feeler gages. The thrust should be evenly

divided between the two sides. If the thrust

clearance is greater on one side than on the

other, the generator housing must be moved

until a balanced condition is attained.

8. Remove the hardwood blocks securing the

crankshaft. Recheck the engine crankshaftthrust bearing clearances and the setting of the

elastic coupling in relation to the center

prickpunch mark. If either the bearing or the

coupling has moved, the condition must be

corrected by moving the crankshaft, the

coupling, or the generator. If any move is

made, it will be necessary to recheck the

engine crankshaft thrust, the coupling, and the

generator thrust bearing.

When all clearances are correct, a strain gage

reading must be taken and checked against the

recorded original reading. A change in the

strain gage reading indicates misalignment, a

condition which, at this point, can be corrected

only by moving the generator.

After perfect alignment has been attained,

measure the space between the generator feet



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Documents

Chapter 11 - Jounals Bearings and Aligment