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.

CONTACT POINT DISTRIBUTOR 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