TM  55-2840-241-23 Table  4-1.  Troubleshooting  (Continued) Item Trouble Probable cause Remedy 50.1 b. (cont) c. 51 Main rotor does not a. Deleted. b.    Deleted. Binding  of  gearbox. c. Replace engine. (Refer to TM   55-1520-228-23.) Dirt  or  sand  between a. Blow out with compressed air. rotate  by  30%  N1. fourth  stage  turbine wheel  and  shroud. b. Turbine blade tip (N2) b.  Shutdown.  Repeat  start rub. procedure. If not rotating after third attempt, replace engine. (Refer to TM   55-1520-228-23.) c.  Carbon  formation c. Shutdown. Ensure that the oil around  rotating being used is MIL-L-7808F or G, or labyrinth  seals. MIL-L-23699. Repeat start procedure. If not rotating after third attempt, replace engine. (Refer to TM   55-1520-228-23.) 52 Unable to obtain maximum  N2  rpm. 53 Engine  tubing cracked or broken at the  flare. 54 Power turbine governor  and  gas producer fuel control throttle shaft binding. 55 Power  loss,  N2  droop or  flameout. a. Air leak in control air tubes. b. Improper control rigging. c. Faulty power turbine governor. d.  Fuel  obstruction, Excessive   vibration. Corrosion  buildup  on shaft causing a tight fit in the throttle shaft bushing. a. Improper rigging. a. b. c. Tighten  tube  fittings. Check  rigging. Replace governor. (Refer to para 5-13.) d. Inspect, flush and/or replace fuel lines in system. (Refer to Chapter 5.) Check the engine for possible vibration causes. (Refer to the vibration  inspections  in  para  12-8.) Apply  (Item  36,  Table  2-2)  to  the area  shown  in  figure  4-3  and  figure 4-4; a one second spray should be sufficient. Rotate shaft, back and forth,  following  spray  to  assure penetration. Repeat spray if necessary. Refer  to  para  4-3. b. Cracks, scratches, and dents. c. Improper sealing or sealing   surfaces. 4-12.2 Change  15