TM9-2815-202-34 6-34.  PISTON  AND  CONNECTING  ROD  MAIN TENANCE  (TRUNK  TYPE)  (Cont) (f) Check each piston pin retainer for proper  sealing  with  leak  detector (15). Place suction cup over retainer  and  hand  operate  lever to pull a vacuum of ten inches of mercury on gage. A drop in gage reading  indicates  air  leakage  at retainer. (2) Installation - Piston Rings NOTE Before  installing  piston  rings, assemble  piston  and  rod  as  directed in  previous  section. (a) Lubricate piston rings and piston l l with engine oil before installing rings. CAUTION Do  not  overlap  ends  of  oil  control  ring  expanders.  An  overlapped  expander  will cause  oil  control  ring  to  protrude  beyond  allowable  limits  and  result  in  breakage when  inserting  piston  in  ring  compressor. Do not cut or grind ends of expanders to prevent overlapping. Cutting or grinding ends  will  decrease  expanding  force  on  oil  control  rings  and  result  in  high-lubricating oil  consumption. NOTE Scraper edges of all oil control rings must face downward (toward bottom of piston) for proper  oil  control. (b) Install two ring expanders (16) in oil control ring grooves in piston (10). Install oil ring expanders with legs of free ends toward top of piston. WARNING Do not grasp or graze sharp edges of oil control rings with bare hands. Rings  are  extremely  sharp  and  can  cut  personnel  when  mishandled. l l 6-38 NOTE Upper  oil  control  ring  groove  requires  a  one-piece two-piece ring (upper and lower halves). Install upper and lower oil control rings by hand. ring, and lower groove requires a Scraper edges of all oil control rings must face downward (toward bottom of piston) for proper oil control.