TM 10-3930-669-34 15-7.  MAST PRIMARY CYLINDER REPAIR (CONT). (5) Remove cylinder (1) from chain vise, rotate  180 degrees, and position cylinder in chain vise. CAUTION Keep  piston  straight  and  concentric in  cylinder.    Do  not  allow  piston  to become wedged in cylinder or damage   to   cylinder   or   piston   may occur. (6) Install wear ring (8) on piston (5). (7) Install piston (5) in cylinder (1). (8) Install preformed packing (7) on base (3). (9) Install backup ring (6) on base (3). (10) Install two screws (2) in base (3). (11) Position base (3) in cylinder (1) with hole in base visible in slot of cylinder. WARNING Use  extreme  care  when  removing  or installing   lock   wire.      Lock   wire   is under    tension    and    can    act    as    a projectile    when    released    suddenly. Ensure proper eye protection is worn to prevent injury to personnel. (12) Install  lock  wire  (4)  in  hole  of  base  (3)  rotating base until lock wire locks into groove of base. (13) Remove two screws (2) from base (3). (14) Remove   mast   primary   cylinder   (1)   from   chain vise. NOTE Follow-on Maintenance: • Install mast primary cylinder (Para 13-2). END OF TASK 15-50