K. Find the Balance Correction Weight (W2)
SUBTASK 72-31-00-975-020-G00
(1) On polargraph paper, G51119, (Figure 508), draw a vector to show the initial imbalance (Uo) at
the initial phase angle (Ao).
SUBTASK 72-31-00-975-021-G00
(2) Draw a vector to show the imbalance (U1) at phase angle (A1) from run number 2.
SUBTASK 72-31-00-975-022-G00
(3) Draw a line that connects the vector tips, from Uo to U1. This line is R1.
SUBTASK 72-31-00-975-023-G00
(4) Measure and make a record of the length of R1 (in units of mils).
SUBTASK 72-31-00-975-024-G00
(5) Measure the angle from R1 to Uo. This is the correction angle (X).
NOTE: If you do not have a protractor, you can find the angle by transposition. Extend vector
Uo through the center of the polar plot. To transpose R1, draw a line parrelel to R1
through the center of the plot. Find the angle (X) and the direction from R1 to Uo.
(Figure 509).
(a) Make a record of the angle and its clockwise direction from R1 to Uo.
SUBTASK 72-31-00-975-025-G00
(6) To find the position to install weight (W2), divide the correction angle found in above step by
9.5°.
NOTE: 9.5 is used because 360° divided by 38 screws = 9.5° between screws.
SUBTASK 72-31-00-975-026-G00
(7) Calculate (W2) as follows:
W2 = W1 X (Uo/R1)
SUBTASK 72-31-00-975-027-G00
(8) Use the table of balance screw weights (Figure 505) to make a selection of the screw or
screws necessary to equal W2.
L. Install the balance correction screws (W2) as follows:
SUBTASK 72-31-00-945-021-G00
(1) Put protective mats, STD-6378 on the bottom half of the internal inlet cowl.
SUBTASK 72-31-00-035-028-G00
(2) Remove the W1 balance screws.
SUBTASK 72-31-00-435-029-G00
(3) Install the initial screws that were replaced by the W1 screws.
(a) Tighten the screws to 50-75 pound-inches (5.6-8.4 newton meters).
SUBTASK 72-31-00-035-030-G00
(4) Remove the screws to be replaced by the W2 screws.
(a) Make a record of the location of each of the screws that you remove.
(b) Keep the screws because it is possible you will have to put them back (in the same
location).
SUBTASK 72-31-00-435-031-G00
(5) Install the W2 screws.
767
AIRCRAFT MAINTENANCE MANUAL
CF6-80A SERIES ENGINES
72-31-00
NoC
Page 506
D633T1B7 Aug 22/2017
ECCN 9E991 BOEING PROPRIETARY - Copyright © Unpublished Work - See title page for details
EFFECTIVITY
ABX 001-007, 011, 012, 016-019, 021, 022, 025, 101,
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