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 to know 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

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
other time 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

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 following discussion
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 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

such as camshafts, 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 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 used for
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-

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.
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

shells are either forged or cast, and the
linings are made of lead-base babbitt
metal.

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
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

necessary to file down the high spots
rather than scrape them down as is
possible with softer bearing metals.
11A6. Bearing failures. When an
engine bearing 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.

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 foreign
matter 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

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 is not immediately known,
the oil supply to
of the salt water in the system should be
determined. At the first opportunity the
system should 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, the condition 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,

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 to stop 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 -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, or repairs 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:

There have been cases where journals
were wrapped with old rags or burlap
that contained some acid. The action of
this acid 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 clearance exceeds 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.