taking a reading on the opposite shaft. Indicator brackets are available that allow the indicator to
be attached directly to the shaft, indicating off the indicator bar. This arrangement reduces bar
sag and eliminates inaccuracies caused by poor surface condition of the shaft. From the data
obtained by the reverse indicator method, it is possible to determine, either analytically or
graphically, the movement or shims necessary to align the shafts. A graphical method is presented
below using the Reverse Indicator Alignment Worksheet
Record Indicator Readings
1. Attach indicator bars and indicators to shafts and position shafts so that the pump indicator,
that is the indicator nearest the pump, is on top and the motor indicator is on the bottom. By
increasing the span between the indicators, the accuracy of the readings can usually be increased,
although bar sag may also increase. Zero both indicators at this position.
2.Rotate both shafts, preferably in the direction of normal rotation, and record the indicator
readings at 90-degree intervals. For consistency, right and left readings should be designated for
both shafts looking from the pump end towards the motor end. Both indicators should read zero
at 360 degrees. If not, zero indicators and retake readings.
It is very important to record
reading is positive or negative and to keep track of each
value's sign while
performing the addition and subtraction in
the following steps.
3. To correct for bar sag, add twice the actual amount of sag to the bottom readings.
4. Subtract the top reading from the corrected bottom reading and the left reading from the right
reading and divide the differences by two. These values will be used for plotting the position of
1. Two graphs will be needed: one for the horizontal plane (top view) and one for the vertical
plane (side view). The horizontal scale of both graphs will represent the horizontal distance from
the plane of the pump indicator to the plane of the rear motor feet. Since the pump shaft will not
be moved, it will be used as the horizontal reference in determining the position of the motor
shaft. The vertical scale will represent the misalignment of the motor shaft.
2. Establish the horizontal scale, marking with vertical lines the relative position of both indicators
and the front and rear motor feet. Draw two horizontal lines representing the pump shaft
reference line for the horizontal and vertical planes. A vertical scale of 0.001 inch per division is
3. Plot the values from step 4 above. These values represent the vertical distance from the pump
shaft line to the motor shaft line at each of the indicator locations. The top-bottom readings are
used in the vertical plane plot, and the left-right readings are used in the horizontal plane plot.