SPARK PLUG Uses the coils high voltage to create a spark in the engine.

It consists of :

Steel shellCeramic insulatorSide electrodeA center electrode sometimes called a center terminal

SPARK PLUG REACHThe distance from the end of the threads to the tapered seat or sealing surface. This is critical because it determines the position of the spark inside of the combustion chamber.

SPARK PLUGS SIZE

Spark plugs also vary in the size of the thread diameter. 10, 12, 14, and 18mm plugs are being made.Spark plug gap: Older cars will have a gap of 0.030-.035inches with point systems, but newer cars can have gaps of over 0.060inches .

TYPES OF SPARK PLUGHOT SPARK PLUG: Designed with a ceramic insert having smaller contact area with the metal part of the plug. This reduces the heat transfer from the ceramic, making it run hotter and thus burn away more deposits.

COLD SAPRK PLUG: Designed with more contact area, so they run cooler.HEAT RANGE 500-800 Deg. C

IGNITION TIMING

IGNITION TIMING COMPENSATES FOR BURN TIME

IGNITION TIMING FACTORSIgnition timing is how early or late spark plugs fire in relation to position of engine pistonsIgnition timing must vary with engine speed, load and temperatureMust be advanced at times and retarded at other times

IGNITION TIMING MECHANISMDistributor rotor systemLower half of distributor

CONTROL OF IGNITION TIMINGThere are two reasons to focus on ignition timing: To allow sufficient work output. ( W = Pressure*Area*Length of stroke) limited extent of exhaust emissions.(in vehicles where maximum power is not required retardation is used to reduce Nox, which is the main pollutant)

METHODS OF CONTROL OF IGNITION TIMINGDISTRIBUTOR CENTRIFUGAL ADVANCE

DISTRIBUTOR VACUUM ADVANCE

ELECTRONIC (COMPUTER) ADVANCE

CENTRIFUGAL ADVANCEVaries in direct relation to engine rpm

Centrifugal force throws weights out

Allows spark to happen sooner to allow enough time for combustion to take place on power stroke.

VACUUM ADVANCEProvide advance at lower engine speeds and part throttle operation.

Matches timing to engine load.

Controlled by venturi vacuum or manifold vacuumFIG 5-35

ELECTRONIC SPARK TIMINGDistributor does not have a centrifugal or vacuum advance mechanismUses engine sensors as inputs to computerYou must disable spark advance when setting base timing on computer controlled cars

DISTRIBUTORLESS IGNITION SYSTEM

ENGINE FIRING ORDERREFERS TO SEQUENCE SPARK PLUGS FIRECAST INTO INTAKE MANIFOLDEACH ENGINE WILL HAVE DIFFERENT FIRING ORDERMUST USE DURING TUNE-UPFIG 5-3