If inspection reveals signs of water in an engine or in  the  exhaust  manifold,  take  steps  immediately  to correct   the   trouble.   Check   the   unit   for   proper installation. Wet-type silencers must be installed with the proper sizes of piping. If the inlet water piping is too large, too much water may be injected into the silencer. There  must  be  continuous-type  water  drains  on  the silencer. If a silencer has no continuous drain and if the engine is at a lower level than the exhaust outlet, water may back up into the engine. Dry-type  silencers  may  become  clogged  with  an excessive accumulation of oil or soot. When this occurs, exhaust back pressure increases, causing troubles such as high exhaust temperature, loss of power, or possible stalling. A dry-type silencer clogged with oil or soot is also subject to fire. Clogging can usually be detected by fire, soot, or sparks coming from the exhaust stack An excessive  accumulation  of  oil  or  soot  in  a  dry-type silencer  may  be  due  to  a  number  of  factors,  such  as failure to drain the silencer, poor condition of the engine, or improper engine operating conditions. Insufficient Intake Air Insufficient intake air, which may cause an engine to  stall  or  stop,  may  be  due  to  blower  failure  or  to  a clogged air silencer or air filter. Even though all other engine  parts  function  perfectly,  efficient  engine operation is impossible if the air intake system fails to supply   a   sufficient   quantity   of   air   for   complete combustion of the fuel. CLOGGED   AIR   CLEANERS   AND   SILEN- CERS.—Sometimes  an  engine  will  fire  erratically  or misfire because of a clogged air cleaner or silencer. Air cleaners  must  be  cleaned  at  specified  intervals,  as recommended  in  the  engine  manufacturer’s  technical manuals.  A  clogged  cleaner  reduces  the  intake  air, thereby affecting the operation of the engine. Clogged air cleaners may cause not only misfiring or erratic firing but also such difficulties as hard starting, loss of power, engine smoke, and overheating. When you clean an air cleaner element, if you use a volatile solvent, be SURE the element is dry before you reinstall  it  on  the  engine.  Volatile  solvents  are  excellent cleaning agents but, if permitted to remain in the filter, may cause engine overspeeding or a serious explosion. Oil-bath type air cleaners and filters cause very little trouble  if  serviced  properly.  Cleaning  directions  are usually given on the cleaner housing. The frequency of cleaning  is  usually  based  on  a  specified  number  of operating  hours,  but  more  frequent  cleaning  may  be necessary where unfavorable conditions exist. When you fill an oil bath-type cleaner, follow the manufacturer’s  instructions.  Most  air  cleaners  of  this type  have  a  FULL  mark  on  the  oil  reservoir.  Filling beyond this mark does not increase the efficiency of the unit and may lead to serious trouble. When the oil bath is too full, the intake air may draw oil into the cylinders. This  excess  oil-air  mixture,  over  which  there  is  no control, may cause an engine to “run away,” resulting in serious  damage. BLOWER  FAILURE.—Troubles  that  may  prevent a   centrifugal   blower   from   performing   its   function usually  involve  damage  to  the  rotor  shaft,  thrust bearings,  turbine  blading,  nozzle  ring,  or  blower impeller. Damage to the rotor shaft and thrust bearings usually  results  from  insufficient  lubrication,  an unbalanced rotor, or operation with excessive exhaust temperature. Centrifugal  blower  lubrication  problems  may  be caused by failure of the oil pump to prime, low lube oil level, clogged oil passages or oil filter, or a defective relief valve, which is designed to maintain proper lube oil  pressure. If an unbalanced rotor is the cause of shaft or bearing trouble,  there  will  be  excessive  vibration.  Unbalance may be caused by a damaged turbine wheel blading or by a damaged blower impeller. Operating a blower when the exhaust temperature is   above   the   specified   maximum   safe   temperature generally   causes   severe   damage   to   turbocharger bearings and other parts. Make every effort to find and eliminate   causes   of   excessive   exhaust   temperature before the turbocharger is damaged. Turbine  blading  damage  may  be  caused  by operating  with  an  excessive  exhaust  temperature, operating at excessive speeds, bearing failures, failure to  drain  the  turbine  casing,  the  entrance  of  foreign bodies, or by turbine blades that break loose. Damage to an impeller may be caused by thrust or shaft  bearing  failure,  entrance  of  foreign  bodies,  or loosening of the impeller on the shaft. Since blowers are high-speed units and operate with a very small clearance between parts, minor damage to a part could cause extensive blower damage and failure. Although   there   is   considerable   difference   in operating  principle  and  construction  between  the positive-displacement   blower   (Roots)   and   the 3-33