TM 10-3930-669-34 13-2.  MAST ASSEMBLY REPLACEMENT/REPAIR (CONT). WARNING • Secondary  cylinders  weigh  140  lbs  (64  kg)  each.    Attach  suitable  lifting  device  prior  to removal to prevent possible injury to personnel. • All personnel must  stand  clear  during  lifting  operations.    A  swinging  or  shifting  load  may cause injury or death to personnel. (3) Install two secondary cylinders (75 and 76) on outer rail (61). WARNING Use care when removing or installing snap  and  retaining  rings.    Snap  and retaining    rings    are    under    spring tension   and   can   act   as   projectiles when    released    and    could    cause severe eye injury. (4) Install   two   retaining   rings   (74)   on   secondary cylinders (75 and 76). 13-16