adjust  the  valves  periodically.  The  engine  lubrica- tion system supplies a flow of oil to the lifters at all times. These hydraulic lifters operate at zero clear- ance and compensate for changes in engine tem- perature, adapt automatically for minor wear at various points, and thus provide ideal valve timing. The first indication of a faulty hydraulic valve lifter  is  a  “clicking”  noise.  In  one  method  for locating  a  noisy  valve  lifter,  you  use  a  piece  of garden hose. Place one end of the hose near the end of each intake and exhaust valve and the other end of the hose to your ear. In this way you can localize  the  sound,  making  it  easy  to  determine which  lifter  is  at  fault.  Another  method  is  to  place a finger on the face of the valve spring retainer. If the lifter is not functioning properly, a distinct shock will be felt when the valve returns to its seat. Usually, where noise exists in one or more of the valve lifters, you should remove all lifter units, clean  them  in  a  solvent,  reassemble  them,  and reinstall  them  in  the  engine.  If  dirt,  carbon,  or the like, is found in one unit, it more than likely is  present  in  all  of  them;  and  it  will  be  only  a matter of time before the rest of the lifter units will  give  trouble. VALVE   REMOVAL For  such  services  as  valve  or  valve  seat grinding,  valve  seat  insert  replacement,  and  valve guide  cleaning  or  replacement,  you  need  to remove  the  cylinder  head  and  valves  from  the engine.  Avoid  interchanging  valves;  each  valve must be replaced in the valve port from which it was  removed.  A  valve  rack  in  which  the  valves may be placed in their proper order—along with their  valve  springs,  retainers,  and  locks—is normally    provided. Different   tools   and procedures  for  removal  are  used  for  different engines.  Check  the  manufacturer’s  maintenance manual  for  your  particular  engine. VALVE   GRINDING The first step in servicing valves after they have been  removed  from  the  engine  is  to  rid  them  of carbon.  The  best  method  for  doing  this  is  cleaning them  with  a  wire  buffing  wheel  or  brush. WARNING When  using  the  wire  buffing  wheel, always wear goggles to protect your eyes from  wire  or  carbon  that  may  fly  off  the buffing  wheel. After the cleaning process, inspect each valve to determine whether it can be serviced and reused or must be replaced. The valve should be checked with a run-out gauge for eccentricity and inspected for worn valve stem and badly cracked, burned, or   pitted   valve   face.   Minor   pits,   burns,   or irregularities  in  the  valve  face  may  be  removed by  grinding. To grind valves, clamp the valve stem in the chuck  of  the  valve-refacing  machine  so  that  the face of the valve will contact the grinding wheel. (See fig. 3-16.) Set the chuck at the proper angle to give the correct angle to the setting face. This angle must just match the valve seat angle. It is becoming  common,  however,  in  some  engines  to reface the valves at a slightly flatter angle than the  seat,  usually  1/4°  to  1°,  to  provide  what  is known  as  an  “interference   angle.”   This   angle provides  greater  pressure  at  the  upper  edge  of  the valve  seat,  which  aids  in  cutting  through  any deposits  that  form  and  provides  for  better  sealing. Some  engines  use  the  interference  angle  on  the exhaust valve only, and others use it on both the intake   and   exhaust   valves. Check   the manufacturer’s   manual   for   the   recommended angle  for  both  valve  and  valve  seat. CAUTION Because  of  the  different  angles  between the valve and the valve seat, do NOT use grinding  compound  to  finish  the  surface. At the start of the grinding operation, make the first cut a light one. If metal is removed from only one-third or one-half of the valve face, check to make sure you have cleaned the valve stem and grinder chuck thoroughly and centered the valve Figure 3-16.—Valve-refacing machine. 3-17