LINEAR VIBRATION TESTING AND ADJUSTING CORRECTIVE ACTION General If  a  component  is  the  only  item  with  excessive  motion, the component mounting will have to be altered until the motion  is  reduced  to  an  acceptable  level  at  operating rpm. When  the  vibration  motion  measurements  show  that  1/2 order   is   causing   the   problem,   the   engine   fuel   and governing  system  must  be  serviced  to  eliminate  engine misfiring.      No   other   work   should   be   attempted   until engine misfiring is eliminated. When excessive 2nd order vibration occurs on 4-cylinder and   V8   engines,   the   timing   of   the   2nd   order   force balancers should be checked.  Other high order vibration levels cannot be corrected with flywheel balance weights or   balancer   timing.      Usually   these   orders   involve   the structural   characteristics   of   the   generator   and    base which would have to be altered. If    the    vibration    motion    involves    nonengine-mounted structures and the engine vibration motion is acceptable, either    the    off    engine    components    must    have    their mounting altered or proper vibration isolators would have to   be   installed   between   the   generator   set   and   the structure. If   the   entire   unit   has   excessive   motion,   the   following steps   are   required   to   remedy   the   various   types   of vibration.    However,  if  the  vibration  motion  for  1st  and 2nd    orders    only    still    remain    excessive    after    these procedures,  the  engine  should  be  removed  from  the  set and  placed  on  suitable  isolators.    If  the  engine  is  within limits,  a  vibration  specialist  should  be  consulted.    If  the bare   engine   exceeds   the   limits,   engine   components rotating   at   engine   speed   (1st   order)   or   twice   engine speed (2nd order) should be inspected. Misalignment and Unbalance 1. Check   alignment   of   the   unit.      Refer-to   Caterpillar Special    Instructions    for    single-    and    two-bearing generator    installations    instructions.        These    are indexed    under    Section    4450    in    the    Caterpillar Service Department Master Index microfiche system.      The   Special   Instructions   are   also   in   the microfiche system. 2. If    vibration    is    still    excessive,    refer    to    Balance Procedure on Page 6. 3. Should    this    procedure    fail,    the    unit    should    be mounted   on   isolators   and   the   Balance   Procedure repeated   until   a   satisfactory   level   of   vibration   is obtained. Resonance With resonant conditions there are two ways of reducing the vibration level.  These   are:  reduction  of  the  exciting force  and  changing  the  natural  frequency  of  the  unit.    If the    following    checks    show    that    the    structure    the generator set is mounted on is the cause of the problem, a    vibration    specialist    or    mounting    system    specialist should be consulted. 1. Check alignment of the unit. 2. If    vibration    is    still    excessive,    refer    to    Balance Procedure on Page 107. 3. Should    this    procedure    fail,    the    unit    should    be mounted  on  isolators  and  rechecked.    If  the  unit  is satisfactory,  the  problem  is  an  improper  mounting system which requires changing.  Consult the proper specialist. Should  the  balance  procedure  fail  and  the  set  has excessive  linear  vibration  motion  when  installed  on the  proper  isolators,  the  balance  procedure  should be  repeated  until  the  linear  vibration  motion  level  is satisfactory. Torque Reaction 1. This   condition   is   generally   encountered   when   the engine is driving a conventional two-bearing generator    which    is    not    close    coupled.        Check alignment of the unit. 2. If  the  two-bearing  generator  set  utilizes  a  structural steel   base    which    is    point    mounted,    i.e.,    pads, isolators,  etc.,  torque  reaction  can  deflect  the  weak base. This deflection can cause severe misalignment  and  resulting  vibration.    Assuming  the unit continues to exhibit vibration after alignment, the base    is    not    strong    enough    to    hold    the    torque reaction  and  needs  strengthening.    One  method  of strengthening   is   to   weld   plates   on   the   top   and bottom of the base across the width of the base from 6  in.    forward  of  the  rear  engine  supports  to  6  in. behind the generator feet closest to the engine. 106