as the failed part. There are only two ways that could
an unusual noise. Since the majority of the components
cause this shaft to fail: (1) if the shaft has been dropped
are metal, they will readily transmit noise. The noise will
in shipping, installation, or removal, and (2) a
be amplified and will sound as though it is everywhere.
catastrophic failure due to a manufacturer's defect.
For this reason, it is extremely important for you, the
GSM, to make yourself very familiar with every little
REMOVAL AND REPLACEMENT OF COM-
noise that pertains to the unit's operation. Simply stated,
PONENTS. All of the components we have discussed,
you should be able to recognize what is normal so you
except the complete reduction gear assembly and the
will be able to identify a problem if one should occur.
generator drive shaft, can be removed and replaced at
the shipboard maintenance level.
Starter. There are some problems with the starter
that you, the GSM, should be able to diagnose and repair.
The starter, as you know, is removed all the time for
The following list contains a description of these
periodic inspections and maintenance. Therefore, if the
problems and their probable solutions:
starter fails, replacing it is not considered to be a major
1. The starter fails to engage. When this occurs,
you should first check to see if the starter is turning.
On the other hand, the PTO shaft does not fail that
Next, verify the condition of the drive and driven gears.
often and you may never see the time when it will have
Remember, if they are worn excessively they will not
to be replaced. The procedure for replacing the PTO
engage. Also check for proper clearances between the
shaft requires the engine to be removed from its mounts
gear faces. The last item to check is the starter drive shaft
and moved back. Once the engine is moved back far
movement. Is it actually moving out for engagement?
enough to be uncoupled, it must then be angled inside
Most of these problems can be repaired at the shipboard
the enclosure to allow enough access for shaft removal.
level. The exception is if the starter drive fails to move
You will likely be required use an IMA for assistance in
out. In this case, the whole starter must be removed and
As already discussed, the removal and replacement
2. The starter fails to disengage. This condition will
of the generator drive shaft cannot be accomplished at
normally occur when the starter drive binds up in the
the shipboard maintenance level.
extended position or the gear-to-gear clearance is too
PTO Shaft. A problem in the PTO shaft will
probably be one of the easiest to solve. For example, if
You have just read about some of the components,
the midbearing seizes, the shaft assembly is designed to
systems, and maintenance requirements associated with
shear at the taper coupling. This design prevents damage
the electric plants installed on the different gas
to the turbine. After all, a PTO shaft is much cheaper to
turbine-powered ships. You also read about the
replace than a turbine. The following list includes a
o p e r a t i o n s , m a i n t e n a n c e requirements, and
description of symptoms that will appear if the taper
troubleshooting techniques for prime movers, such as
the Allison 501-K17 and K34 models, the Garrett found
on the PHM-class ships, the Sunstrand found on the
1. While attempting a start, the starter engages and
LCAC-class ships, and the Detroit Diesel you will
the reduction gear is rotating, but the turbine is not.
encounter on the FFG-class ships. After reading the
2. While operating, the generator voltages drop
information in this chapter, you should be able to
rapidly and the turbine and reduction gear oil pressure
recognize the similarities among these important units
diminishes because the reduction gear is not turning
and their operating, design, and functional differences.
(CG-, DD-, and DDG-993 class ships). If you are on a
Most importantly, you, as a GSM who may be assigned
DDG-51 class ship, then the generator and reduction
to any of these gas turbine ships, should be able to
gear oil pressures would be affected,
identify your responsibilities for the maintenance,
repair, and operational readiness of these important
Generator Drive Shaft. You will probably never
encounter a problem in which you can pinpoint this shaft