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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
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CFM56 ENGINES
737-300/400/500/ /MAINTENANCE MANUAL ////////////////////////
(k)  If the amplitude of the No.1 bearing (or FFCCV) or the corrected TRF vibration level is more than 8 mils DA, do the steps that follow. 1) Do not read the indications. 2) Decrease the speed until the corrected vibration level is
_________
 not more than 8 mils DA.

 3)  Use the N1 speeds that cause corrected vibration levels that are less than 8 mils DA to do a first trim balance procedure.
 (l)  Decrease the speed slowly and continuously and make the engine stable at the N1 speeds shown in Figure 504. 1) Make sure the vibrations become stable. 2) When the vibrations become stable, write the vibration
 amplitude (U) and phase angle (A) for each sensor and each speed, as shown in the worksheet (Fig. 504).
 NOTE: If the vibration does not become stable in
____ 1 minute, continue the procedure, but do not keep this data.
 NOTE: ENGINES WITHOUT CFMI SB 72-437;
____ Refer to Figure 504 (Configuration 1).
 NOTE: ENGINES WITH CFMI SB 72-437;
____ Refer to Figure 504 (Configuration 2).
 NOTE: A minimum of 3 different speeds are necessary to do
____ a simultaneous 2-plane computation.
 (m)  
Decrease the speed to minimum power.

 (n)  
After 5 minutes, when the engine becomes stable, do the engine shutdown procedure (Ref 71-00-00/201).

 S 825-010-C00
 (2)  Use the one shot plot procedure to decrease the vibration levels.
 (a)  To calculate the results more easily, use only the three
 highest amplitudes for the No. 1 bearing (or FFCCV) and the
 three highest amplitudes for the TRF from the worksheet
 (Fig. 504).

 NOTE: Do not use a vibration amplitude that is less than 1 mil
____ DA. You can use all data from the worksheet, if you will use a computer program to calculate the results.
 (b)  Calculate the imbalance weight and angle location as follows:
 1)  Calculate the related weights and angles for the six highest amplitudes:
 Balance Weight (W) = Amplitude (UO) x Sensitivity Calculated Angle (A) = Phase Angle (AO) + Phase Lag
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CFM56 ENGINES
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2)  Use the letters A thru F as indices for the six points you will use.
 NOTE: For an example, the first point P1, will be referred
____
 to as A, the second point P2, as B.

 3)  Make a selection of applicable graduations, in g-cm, on a polar graph (Fig. 505) that will include all of the balance weights.
 4)  Put the six index points (A-F), and the balance weights (W) at their calculated angles (A) on the polar graph.
 5)  Measure and write the vector length (distance between each pair of points) on the worksheet in Fig. 506.
 6)  Use the data from the worksheet on Fig. 504, to write the sensitivity of each index point (P1 and P2) of each vector on Fig. 506.
 NOTE:____An example for AB is: sensitivity of A (P1) = SP1, sensitivity of B (P2) = SP2.
 a)  Add the two sensitivities for each vector (SP1 + SP2).
 7)  Calculate the amplitude (U) of each vector and write it on Fig. 506:
 U = Length of Vector P1-P2 ------------------------------------------------Sensitivity of P1 (SP1) + Sensitivity of P2 (SP2)
 8)  Use the vector with the maximum amplitude to calculate the distance from the start of the first vector (P1), to the balance point W1.
 NOTE: The distance from P1, dP1 = U x (SP1)
____
 a)  Write the value, dP1, on the worksheet (Fig. 506).
 9)  Start at point P1 and go along the vector P1-P2 on Fig. 505 to put the calculated length, dP1, on the graph.
 10) Make a vector, with a label W1, from the origin (the center of the graph) to the end of dP1 on P1-P2.
 11) Measure and make a record of the length (the imbalance
 weight (g-cm)) and the phase angle (A1) of W1.

 (c) Calculate the residual vibration level as follows:
　
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