(a)
Thermally stabilize the engine with the steps given earlier in this procedure.
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(b) Do the trim balance survey by stopping at the same N1 speeds used during the As-Is Trim Balance Survey and make a record of the data.
NOTE: Refer to PBS-4100 operation manual for instructions
____
on computer operations.
NOTE: PBS-4100 software V2.21 and higher will let you take
____ the trim balance data during the vibration survey. If the software is pre V2.21, the vibration survey and the trim balance can be done separately.
(c) Do a slow decel (90-120 seconds) to IDLE.
NOTE: Trim balance data is only taken during the accel
____
vibration survey.
(d)
Operate the engine at IDLE for five minutes to let the engine become cool.
(e)
Use the Power Plant Operation (Normal) procedure to do the engine shutdown (AMM 71-00-00/201).
(f)
If the vibration levels are satisfactory, do these steps:
1) Return the airplane to service with the steps given later in this procedure.
(g)
If the vibration levels are not satisfactory, do the steps that follow: 1) Use the "PREDICT" feature of the PBS-4100 to find if there
is a balance solution that will decrease the vibration to satisfactory levels. 2) If there is a satisfactory balance solution, Do a Re-Balance with the steps given later in this procedure. 3) If there are no satisfactory balance solutions, remove the engine (AMM 71-00-02/401).
I. Re-Balance (Repeat Shot).
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(1)
Do the Re-Balance (Repeat Shot) as follows:
(a)
Remove the inlet cone (AMM 72-31-01/401).
(b)
Using the "BALANCE WGTS" feature of the PBS-4100, find which weights to remove and to install.
(c)
Temporarily install the correction weights in the fan with the cotter pins.
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(d) If necessary, bend the tab on the clip about 50 percent to install the counterweights to the turbine.
NOTE: Low turbine plane counterweights are installed to
____
the 6th-stage turbine blades.
There are 128 6th-stage turbine blades. With the fan indexed, the No. 1 turbine will be the blade at 12 o'clock position. The blades are numbered 1 through 128 in the clockwise direction.
1) A clip-on counterweight (50N401) is given for the LPT 6th-stage blade shroud. Use as necessary with a maximum number of 10 clip-on weights per engine.
2) Attach the counterweights with a PWA 86302 Hydraulic Bender and a PWA 76855 Hydraulic Pump (See Figure 506).
(e)
Obey the computer instructions to make sure the weights you installed are the same as the solution. 1) If you installed weights that are different from the
balance solution, make sure you change the data in the computer.
(f)
Install the inlet cone (AMM 72-31-01/401).
(g)
Do a Check Run with the steps given earlier in this procedure.
J.
Return the Airplane to Service.
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(1)
Remove the trial balance weights and install the permanent
counterweight(s).
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