1) Return the airplane to service with the steps given later in this task.
(g)
If the vibration levels are not satisfactory, do the steps that follow: 1) Input the trim balance data from Figure 506 to a trim
balance computer program.
NOTE: The PBS-4100 computer can be used if software
____ 2.25 and higher is installed. This software allows the manual input of the trim balance data.
2) Calculate the quantity and location of the counterweight for each speed and find the quantity and location that will decrease the vibration to satisfactory levels.
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3) If there is a satisfactory balance solution, do a Re-Balance with the steps given later in this task. 4) If there are no satisfactory balance solutions, remove the engine (AMM 71-00-02/401).
I. Re-Balance (Repeat Shot).
S 975-094-N00
(1)
Do the Re-Balance (Repeat Shot) as follows:
(a)
Remove the inlet cone (AMM 72-31-01/401).
(b)
With the calculated results from the trim balance computer, adjust the quantity and location of the trim balance counter-weights.
(c)
Temporarily install the correction weights in the fan with the cotter pins.
(d)
Install the inlet cone (AMM 72-31-01/401).
(e)
Do a Check Run with the steps given earlier in this task.
J.
Return the Airplane to Service.
S 825-095-N00
(1)
Remove the trial balance weights and install the permanent counterweight(s).
(a)
Install the permanent fan weights as follows: 1) Remove the front segment of the inlet cone (AMM 72-31-01/401). 2) Vibro peen the letters "TB" on the inner diameter face of all the trim balance counterweight(s). 3) Install each permanent fan weight with a rivet. a) Use the riveter to make a 0.125 inch (3.175 mm) diameter head on the rivet.
4) Install the front segment of the inlet cone (AMM 72-31-01/401).
(b)
Operate the engine with the counterweights installed to make sure that the engine vibration is within limits.
TASK 72-31-00-725-096-N00
4. Balance the Front Balance Plane (Trim Balance - PBS-4100 / AVM Procedure)__________________________________________________________________________
A. General
(1)
It is recommended that this trim balance procedure be done by personnel that are trained in the use and operation of the PBS-4100 portable trim balancing system and have experience with engine trim balance.
(2)
This procedure uses the aircraft AVM and the Mechanical Technologies Portable Balancing System (PBS-4100). The PBS-4100 is plugged into the AVM signal conditioner. The PBS-4100 collects the vibration data and calculates a balance solution. This method is used to lower fan ("A" flange) vibration levels only. This procedure should not be used to correct cabin noise problems.
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////////////////////////A / PW4000 SERIES /747-400 / ENGINES/MAINTENANCE MANUAL ////////////////////////
(3) (4) (5) Trim balance can decrease engine vibration. The trim balance procedure adds a small amount of weight to correct unbalance. The weight(s) are installed on the compressor front balance plane. The trim balance procedure can be done on the engine while it is on the airplane.A fan plane balance will affect the low rotor vibration levels on both the fan ("A" flange) and turbine ("P" flange) cases. Because the AVM only has vibration pick-ups on the fan case, the affect of a fan plane balance on the turbine case will not be known. Therefore, this procedure has a limit of the qunatity of weight that can be installed to the fan balance flange. A turbine plane balance cannot be done with this procedure.Trim balance is only used to correct stable low rotor related (1EL) vibration.
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