block can be a very time consuming process. Anytime the thrust block is removed, it
should be allowed to cool overnight before any readings are taken. As several shim
changes may be required, it may take several days to achieve the desired results.
The easiest place to shim is between the thrust runner and the thrust block. Many times, the
shims may be installed by jacking the unit and unbolting the thrust runner, letting it down
on the thrust shoes. Some problems have been noted with shims installed between the
runner and the block, such as fretting corrosion and the shims coming loose. If the runner
is not bolted to the thrust block, all options should be evaluated before installing the shims
between the thrust block and runner. The placement and thickness of the shims should be
calculated to form a wedge to prevent distortion of the thrust runner.
Installing the shims between the shaft and the thrust block is another consideration. This
requires removing the thrust block for every attempt at changing the shim. As the fit is
already a shrink fit, the addition of a shim can be very difficult. Also, the effect of a given
shim is not always predicable. It will likely take several attempts to make the runout
If the thrust block is of the type shown in figure 8, the shim can be placed on the shoulder
on the shaft. This still requires removing the thrust block every time, but it is more
predictable than installing the shim between the shaft and the block.
On units with shims installed in the thrust blocks, attention should be paid to vibration
levels measured at the guide bearings. An increase in vibration may mean that the shims
have shifted or been damaged.
7. ALIGNMENT PROCEDURES
Procedure for Spring Loaded, Semi-Rigid, and Solid Plate
a. Take plumb readings with the shaft in the zero degree position and plot the shaft
profile. If dogleg or offset is excessive, make corrections as discussed in section 6.2.
Take clearance readings of the turbine seal rings, turbine bearing housing, generator
stator, and generator guide bearing housings, if not adjustable. Plot the centerlines of
the static components on the shaft plumb plots to determine concentricity. The
concentricity should be checked even if the stationary components were centered with a
single plumb wire with the rotating components removed.
b. Take static runout readings using either Method I or II. If the magnitude of static runout
exceeds the tolerance in table 1, make necessary corrections as discussed in section 6.6.
Plot the runout readings and, using the plumb plot, determine the position of the center
of runout relative to the shaft at the thrust bearing elevation.