TM 1-1500-204-23-1 9 Examine  magneto  ground  leads  to determine that RIGHT switch position fires front plugs and LEFT    switch    position    fires    rear    plugs.        Make    this examination    prior    to    changing    spark    plugs,    making ignition  harness  test  on  cylinders  which  are  operating,  or are operating intermittently.  In addition, examine ignition leads. NOTE In cases where the cylinder is completely dead on the BOTH position,  the  difficulty  may  be  due  to incorrect valve clearances, impeller oil seal leaks, leaking intake pipes, or lack of compression (blowby). 10 Repeat    cold    cylinder    check    for other magneto positions on Ignition switch when necessary.        Additional    cold    cylinder    checks    will    be conducted  at  different  speeds  in  event  any  roughness  Is still encountered during ignition system check NOTE Cooling of the engine between checks is not necessary as airflow created by propeller and cooling effect of incoming fuel-air mixture into cylinder will be sufficient to cool any cylinders which  are  functioning  on  one  check and  fail  to  function  on  the  following check. (g) Chalk test.  The chalk test should be used when the cold cylinder tester is not available.  Test using the following procedures. 1 Mark  each  cylinder  with  a  piece  of white marking chalk, A-A-320. 2 Run engine as outlined in paragraph (e) above. 3 Examine   each   mark   after   engine shutdown.    Cylinders  having  marks  unchanged  In  color are  dead  or  operating  intermittently.    The  marks  for  a normal operating cylinder will change to a pink color. (h) Cylinder  repair.    Cylinder  repair  can be  accomplished  by  using  the  following  procedures  as applicable CAUTION Do not damage adjacent fins Inadequate cylinder cooling may result. 1 Repair  cracked,  nicked,  or  broken cooling   fins   by   profiling   damaged   area   using   a   file   to smoothly  round  all  edges.    Corners  shall  have  at  least  a 1/4-inch  radius  and  removed  area  nut  shall  not  exceed one percent of the total fin area. NOTE Magnetic or dye-penetrant inspect fins that are profiled to outside of dome to ensure that crack does not extend into cylinder dome. 2 Repair   broken   or   loose   studs   in tapped hole by using helical inserts. NOTE When more than two adjacent nuts are known    to    have    been    loose    during engine  operation,  or  when  more  than two adjacent studs have failed, cylinder will be replaced and all studs on the cylinder mounting pad replaced. 3 Place cover on a surface plate and, using a feeler gauge, measure clearance between surface plate  and  rocker  box  cover  mounting  surface.    Refer  to the applicable maintenance manual for allowable limits. NOTE Accomplish   procedures   4,   5,   and   6 when surface does not meet specified limits. 4 Place    a    small    amount    of    valve grinding compound, A-A-1203, on a lapping plate. NOTE In the event no grinding compound is available, a fine abrasive cloth, Federal Specification P-C-451, may be used. 7-13