kk. For UH-60L helicopters and EH/UH-60A helicopters with balancing kit installed, vibration levels shall be 0.50
ips or less. If vibration levels are within this range, engine output shaft is balanced. Remove the
accelerometers, cables and brackets from the input modules. If vibration level is between 0.50 ips and 2.0 ips,
balance engine output shaft in accordance with task 9. If vibration level is greater than 2.0 ips, replace output
shaft using procedures in TM 1-1520-237-23.
PROCEDURE 4: ENGINE OUTPUT SHAFT ROTATION
FLIGHT SAFETY PART
Verification of proper vibration level is a critical
Refer to procedures in Technical Manual TM 1-1520-237-23 for engine output shaft rotation.
Repeat procedure 3 to re-check engine output shaft vibration after each corrective action that is implemented
per TM 1-1520-237-23. Aircraft is acceptable when vibration levels for both engine output shafts are 1.3 ips or
PROCEDURE 5: OIL COOLER VIBRATION ADJUSTMENTS
The following procedure provides adjustments to reduce vibrations associated with the oil cooler assembly. This
procedure should be performed when procedure 3: Engine Output Shafts and Oil Cooler Testing indicates that an oil
cooler vertical or fore-aft vibration level of greater than 1.0 ips is present.
Ensure proper hardware is installed and flexible coupling, both in front of as well as behind oil cooler assembly,
are shimmed properly (refer to TM 1-1520-237-23). Shim if necessary. Re-check vibration levels.
Re-index drive shaft, rear of oil cooler assembly, 120 degrees clockwise.
Re-check vibration levels. If level is above 1.0 ips, re-index drive shaft 120 degrees clockwise.
Re-check vibration levels. If a reading above 1.0 ips occurs, index drive shaft to the position that results in the
lowest vibration level.
Ensure that viscous damper is shimmed so that no axial pre-load exists in the tail rotor drive shaft or the oil
cooler assembly. Adjust if necessary. Re-check vibration levels.
Check oil cooler drive shaft runout, refer to TM 1-1520-237-23. If runout is over the 0.010-inch limit, adjust
drive shaft. Re-check vibration levels.
If vibration levels remain above 1.0 ips, replace oil cooler.
If drive shaft or oil cooler drive shaft was re-indexed, reinstall spline wear indication system, refer to TM 1-