TM 55-2840-241-23 7-6           Change 19 Figure  7-3.  Compressor Vane Erosion   NOTE This  inspection  requires  removal  of  a  com- pressor case half and shall be performed only for the reasons stated in paragraph 6-2. a. Cracks  are  acceptable  without  limitation  as  to length  and  quantity  provided  the  plastic  is  securely bonded to the case, except cracks along the horizontal splitline in excess of 1/2 inch are unacceptable. b. Debonded, missing, or loose plastic in the vane row areas only is acceptable provided that no more than 50 percent in stages 5 and 6 or 25 percent in stages 1 through 4 are missing. Any raised or loose plastic in the vane row areas shall be removed. c. Raised  or  debonded  plastic  in  the  blade  path areas as not acceptable. Circumferential cracks at the front or rear of the blade path can cause an arc segment of the plastic to raise when at normal operating tempera- tures and cause plastic wear in line with the leading or trailing edge or the blade tips. A groove worn in the plastic adjacent  to  a  circumferential  crack  is  evidence  of  de- bonding in the blade path. d. Erosion of the plastic coating is acceptable un- less bare metal in the lower half is exposed. 7-12.   Compressor Front Support Inspection.   Visually  inspect  the  compressor  front  support.  Re- place the engine if any of the following conditions are found. a. Any cracks in the parent metal or braze joints. If cracks are suspected, refer to TM 1-1520-254-23, Tech- nical Manual Aviation Unit Maintenance (AVUM) and Avi- ation Intermediate Maintenance (AVIM) Manual Nonde- structive  Inspection  Procedure  for  OH-58  Helicopter Series. b. Gradual dents exceeding 1/16 in. deep, or acute dents exceeding 1/32 in. deep. No punctures allowed. c. Weld  failures  at  the  trailing  edge  spacers,  as viewed from the rear with the compressor case half re- moved. d. Vane erosion to the extent that reduction of skin thickness is apparent and/or trailing edge slots are re- stricted. e. Bullet  nose  dents  with  nicks  or  scratches  on dome over 0.020 in. deep after stone blending and fine abrasive paper polishing. 7-13.   Diffuser Scroll Inspection.   Visually  inspect  the  installed  diffuser  scroll  for  the following conditions. Replace the engine if the damage cannot be repaired. a. Inspect for visible cracks. Replace the engine if cracks are found. If cracks are suspected, refer to TM 1-1520-254-23, Technical Manual Aviation Unit Mainte- nance (AVUM) and Aviation Intermediate Maintenance (AVIM) Manual Nondestructive Inspection Procedure for OH-58 Helicopter Series. NOTE The turning vanes and air tube inserts may be inspected only when the combustion section is removed. b. Check the turning vanes in the outlet ports for evidence of damage. Damage is indicative of impeller vane up or shroud failure. Replace the engine. c. Inspect the diffuser scroll discharge air tube in- serts for wear and looseness. If wear in the ID of the insert exceeds 0.010 in. depth or there is evidence that the insert has been pulled out of the scroll, replace the engine. 7-13.1   Diffuser Vent Tube.    Visually  inspect  for  cracks,  bends,  and  dents.  No cracks, dents or bends are permitted. Replace vent tube. If   cracks   in   vent   tube   are   suspected,   refer   to   TM 1-1520-254-23, Technical Manual Aviation Unit Mainte- nance (AVUM) and Aviation Intermediate Maintenance (AVIM) Manual Nondestructive Inspection Procedure for OH-58 Helicopter Series. Inspect the tube for movement. None is permitted. Remove and replace tube. 7-14.   Gearbox Inspection.   Visually  inspect  the  exterior  of  the  gearbox  for  the following conditions. a. Check for cracks in the gearbox housing and cov- er, especially in stress areas; engine mounts, accessory pads, and at the splitline. If cracks are found, replace the engine. If cracks in gearbox housing or cover are sus- pected,  refer  to  TM  1-1520-254-23,  Technical  Manual Aviation Unit Maintenance (AVUM) and Aviation Inter- mediate Maintenance (AVIM) Manual Nondestructive In- spection Procedure for OH-58 Helicopter Series. b. Check  for  oil  leaks.  If  area  below  seal  at  any accessory or power takeoff pad (figure 7-4) is dripping, replace the, seal assembly. (Refer to paragraph 7-27.)