TM  10-3930-643-34 BRAKE  TROUBLESHOOTING  AND  MAINTENANCE. 8-14. Air Compressor. (Sheet 10 of 13) CLEANING/INSPECTION 48. 49. 50• 51. 52. Inspect bearing cap (35) for cracks or damage. Replace if cracked or damaged. Inspect cylinder head  (5)  for deposits or foreign matter. Carbon deposits in air inlet and exhaust cavities must be removed. Heavy accumulations  of  rust or foreign matter in water passage must be removed. A light coating of rust is acceptable. Inspect valve seat surfaces for scratches,  burrs  or imperfections. Slight imperfections may be removed with a stone. Inspect valves (2,8 and 13), two guards (12) cages (11) and seats (7) for nicks, burrs, pitting  or roughness. Minor defects may be removed  with  lapping  equipment. Pin in two guards (12) must be a tight fit in pin hole. Using a micrometer, measure free length of two springs (10).   Free length should be 0.97 inch.    Apply load of 3.5 lbs to two springs (10). Using  hydraulic  pliers,  measure  test length. Test length should be 0.73 inches. Go to sheet 11 8-71