to the next code letters. If a blade requires replacement, the  diametrically opposite blade must also be replaced. Computer  programs generally determine the location for turbine blades  for turbine wheels on modern engines. After removing the required components, the first stage  turbine blades and turbine nozzle vanes are accessible  for inspection. The blade limits specified in the engine  manufacturer’s overhaul and service instruction manual  should he adhered to.  Figure 10-69  shows where cracks  usually occur on a turbine nozzle assembly. Slight nicks and  dents are permissible if the depth of damage is within limits. Inspect the nozzle vanes for nicks or cracks. Small nicks  are not cause for vane rejection, provided such nicks blend  out smoothly. all the blades have been numbered. Mark a number 1 on the  face of the hub on the turbine disk. The number 1 blade is then  installed adjacent to the number 1 on the disk.  [Figure 10-68] The remaining blades are then installed consecutively in a  clockwise direction, viewed from the rear face of the turbine  disk. If there are several pairs of blades having the same  code letters, they are installed consecutively before going  Inspect the nozzle vane supports for defects caused by the  impingement of foreign particles. Use a stone to blend any  doubtful nicks to a smooth radius. Like turbine blades, it is  possible to replace a maximum number of turbine nozzle  vanes in some engines. If more than the maximum vanes  are damaged, a new turbine nozzle vane assembly must be  installed. With the tailpipe (exhaust nozzle) removed, the rear  turbine stage can be inspected for any cracks or evidence of  blade stretch. Additional nozzle stages can also be inspected  with a strong light by looking through the rear-stage turbine. Checking the clearances is one of the procedures in the  maintenance of the turbine section of a turbine engine.  The manufacturer’s service and overhaul manual gives the  procedures and tolerances for checking the turbine. Turbine  clearances being measured at various locations are shown  in  Figures 10-70  and  10-71 . To obtain accurate readings,  special tools provided by each manufacturer must be used  as described in the service instructions for specific engines. The exhaust section of the turbine engine is susceptible to  heat cracking. This section must be thoroughly inspected  along with the inspection the combustion section and turbine  section of the engine. Inspect the exhaust cone and exhaust  nozzle for cracks, warping, buckling, or hotspots. Hotspots  on the tail cone are a good indication of a malfunctioning  fuel nozzle or combustion chamber. The inspection and repair procedures for the hot section  of any one gas turbine engine share similarities to those  of other gas turbine engines. One usual difference is the  nomenclature applied to the various parts of the hot section by the different manufacturers. Other differences include the  manner of disassembly, the tooling necessary, and the repair  methods and limits. 10-53 Exhaust Section Clearances Turbine Nozzle Inlet Guide Vane Inspection Figure 10-67.  Typical turbine rotor blade moment-weight  distribution.  DK 1 D V 54 DU 53 DU 52 DU 51 DU 50 DU 49 DU 48 DT 47 DT 46 DT 45 DS$_{44}$ DR$_{43}$ DR 42 DP 41 DP 40 DN 39 DN 38 DM 37 DM 36 DM 35 DL 34 DL 33 DL 32 DL 31 DL 30 DK 29 DK 28 D V 27 DU 26 DU 25 DU 24 DU 23 DU 22 DU 21 DT 20 DT 19 DT 18 DS 17 DR 16 DR 15 DP 14 DP 13 DN 12 DN 11 DM 10 DM 9 DM 8 DL 7 DL 6 DL 5 DL 4 DL 3 DK 2 Spherical indent on face of disks C l o c k w i s e Viewed from rear Figure 10-68.  Turbine blades. 