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ENGINE DIVISION SERVICE MANUAL TM 5-4210-230-14&P-1 ENGINE the  valve  gear  length  increases,  as  caused  by  lower  engine temperatures,   the   plunger   spring   keeps   all   the   valve   gear parts  in  contact,  increasing  the  clearance  volume  under  the plunger.    At  the  same  time  oil  is  immediately  fed  past  the check    valve,    thus    maintaining    correct    length    under    all conditions.    This  keeps  the  valve  gear  operating  at  no-lash. With this predetermined leakage, is impossible for the no-lash lifter to hold the engine valve open when it should be closed. When the lifter body is on the base circle of the cam and the engine valve is closed, the only force tending to hold the    valve    open    is    from    the    light    plunger    spring,    which obviously is much lower than the valve spring load.  The only additional  force  tending  to  push  the  plunger  upward  results from  pressure  of  the  lubricating  oil  but  its  effect  is  negligible since it is controlled and only acts on the small plunger area. During shutdown periods of the engine, one or more valves are always in the lifted position thus imposing the full valve spring load on the plunger.  This causes oil to leak out of  the  compression  chamber  through  the  clearance  space. When  the  engine  is  again  started,  the  particular  valve  that was in the open position returns to its seat and the plunger is immediately forced upward by its spring.  Oil from the supply chamber  is  again  fed  into  the  clearance  volume  under  the plunger   so   that   in   a   very   few   cycles,   the   valve   gear   is operating on a solid hydraulic oil column. II. When to Service A. Loud  clacking,  light  clicking  or  intermittent  noise  is attributed to a lifter. Dirt,  chips,  varnish,  etc.,  generally  cause  only  a  few units    to    become    inoperative    at    any    one    time. Aeration caused by high or low oil level air leaks into the   oil   pump   suction   line,   etc.,   result   in   all   lifters becoming   noisy.      The   cause   of   aeration   must   be corrected before the lifters will again operate quietly. Small metal chips lodging between the plunger and the  cylinder  tend  to  prevent  free  movement.    Since loads during    the    lift    portion    of    the    cycle    are relatively  high,  the  plunger  is  forced  downward  and the very light plunger spring has insufficient force to move the plunger back to normal operating position. After  a  few  lift  cycles  with  metal  chips  between  the plunger  and  cylinder,  the  plunger  finally  reaches  a position  (usually  plunger  bottomed)  where  there  is excessive  lash  in-the  valve  train  with  resulting  noisy operation. The   type   of   varnish,   resulting   from   a   mixture   of permanent   antifreeze   and   oil,   is   very   "tacky"   and, particularly when cold, will prevent free movement of the plunger.  The resulting action is the same as that caused by a chip in the clearance space.  The entire engine must be cleaned and the cause of the leakage corrected. Varnish     of     the     type     resulting     from     fuels     and lubricants, unless excessive amounts are created by poor crankcase ventilation or extremely bad lubricants,    seldom    causes    sticking    in    the    lifter. However, if such deposits do form and cause trouble, it is then necessary to correct crankcase ventilation, lubricant or fuel. 1. Loud  clacking  noise  is  the  result  of  excessive  lash and indicates that: a. The   plunger   is   stuck   below   its   normal   operating position, probably plunger bottomed and in this case, the  lifter  must  be  disassembled  and  cleaned  of  dirt and varnish. b.     The check valve may not be sealing due to dirt or a damaged seat, which also necessitates cleaning and inspection. c.     Oil may contain sufficient air, which is compressible, to    permit    collapse    or    partial    plunger    movement beyond its normal operating position.  It is necessary to  locate  and  correct  the  cause  of  aeration.    Just servicing the lifter will not help. 2. Light clicking type noise indicates that the plunger is operating  only  slightly  below  its  normal  position  as the result of: a.     Slight leakage by the check valve or plunger.  If the noise    is    persistent,    the    lifter    must    be    removed, cleaned and checked. CGES-210  Page 45 PRINTED IN UNITED STATES OF AMERICA

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