slightly, as it is pulled in and out of the gap. Spark plug gaps vary from 0.30 inch on contact point ignitions to over 0.60 inch on electronic ignition systems. When the spark plugs are being reinstalled, tighten them  to  the  manufacturer’s  recommendation.  Some manufacturers  give  spark  plug  torque,  while  others recommend bottoming the plugs on the seat and then turning  an  additional  one-quarter  to  one-half  turn.  Refer to  the  manufacturer’s  service  manual  for  exact procedures. A  faulty  spark  wire  can  either  have  a  burned  or broken   conductor,   or   it   could   have   deteriorated insulation.  Most  spark  plugs  wires  have  a  resistance conductor that can be easily separated. If the conductor is broken, voltage and current cannot reach the spark plug.  If  the  insulation  is  faulty,  sparks  may  leak through   to   ground   or   to   another   wire   instead   of reaching the spark plugs. To test the wires for proper operation, you can perform the following: A  SPARK  PLUG  WIRE  RESISTANCE  TEST will  check  the  spark  plug  conductor  or  coil  wire conductor. To perform a wire resistance test, connect an ohmmeter across each end of the wire. The meter will read   internal   wire   resistance   in   ohms.   Typically resistance should NOT be over 5,000 ohms per inch or 100.000  ohms  total.  Since  specifications  vary,  compare your readings to the manufacturer’s specifications. A  SPARK  PLUG  WIRE  INSULATION  TEST checks  for  sparks  arcing  through  the  insulation  to ground. To perform an insulation test with the hood up, block out as much light as possible, start the engine, and move a grounded screwdriver next to the insulation. If a spark jumps through the insulation to the screwdriver, the  wire  is  bad.  Spark  plug  leakage  is  a  condition  in which electric arcs pass through the wire insulation. Installing  new  spark  plug  wire  is  a  simply  task, especially  when  one  wire  at  a  time  is  replaced.  Wire replacement  is  more  complicated  if  all  of  the  wires have been removed. Then you must use engine firing order  and  cylinder  numbers  to  route  each  wire correctly.  Service  manuals  can  be  used  to  trace  the wires  from  each  distributor  cap  tower  to  the  correct spark plug. Distributor Service The distributor is critical to the proper operation of the   ignition   system.   The   distributor   senses   engine speed,   alters   ignition   timing,   and   distributes   high voltage to the spark plugs. If any part of the distributor is faulty, engine performance suffers. DISTRIBUTOR   CAP   AND   ROTOR.—When problems  point  to  possible  distributor  cap  or  rotor troubles, remove and inspect them. The distributor cap should be carefully checked to see that sparks have not been  arcing  from  point  to  point.  Both  interior  and exterior must be clean. The firing points should not be eroded, and the interior of the towers must be clean. The  rotor  tip,  from  which  the  high-tension  spark jumps  to  each  distributor  cap  terminal,  should  not  be worn. It also should be checked for excessive burning, carbon trace, looseness, or other damage. Any wear or irregularity  will  result  in  excessive  resistance  to  the high-tension spark. Make sure that the rotor fits snugly on the distributor shaft. A   common   problem   arises   when   a   CARBON TRACE   (small   line   of   carbonlike   substance   that conducts  electricity)  forms  on  the  inside  of  the distributor  cap  or  outer  edge  of  the  rotor.  The  carbon trace  will  short  coil  voltage  to  ground  or  to  a  wrong terminal lug in the distributor cap. A carbon trace will cause the spark plugs to either fire poorly or not at all. Using   a   droplight,   check   the   inside   of   the distributor  cap  for  cracks  and  carbon  trace.  Carbon trace  is  black  which  makes  it  hard  to  see  on  a  black- colored  distributor  cap.  If  carbon  trace  or  a  crack  is found, replace the distributor cap or rotor. C O N T A C T    P O I N T    D I S T R I B U T O R SERVICE. —In  a  contact  point  distributor,  there  are two  areas  of  concern—the  contact  points  and  the condenser. Bad  contact  points  cause  a  variety  of  engine performance  problems.  These  problems  include  high- speed  missing,  no-start  problem,  and  many  other ignition  troubles.  Visually  inspect  the  surfaces  of  the contact points to determine their condition. Points with burned  and  pitted  contacts  or  with  a  worn  rubbing block  must  be  replaced.  However,  if  the  points  look good,  point  resistance  should  be  measured.  Turn  the engine over until the points are closed and then use an ohmmeter  to  connect  the  meter  to  the  primary  point lead and to ground. If resistance reading is too high, the points are burned and must be replaced. A  faulty  condenser  may  leak  (allow  some  dc current to flow to ground), be shorted (direct electrical connection to ground), or be opened (broken lead wire to  the  condenser  foils).  If  the  condenser  is  leaking  or open,  it  will  cause  point  arcing  and  burning.  If  the condenser   is   shorted,   primary   current   will   flow   to ground  and  the  engine  will  NOT  start.  To  test  a condenser using an ohmmeter, connect the meter to the 2-40