Correct Fitment

A spark plug is an important part of the ignition system as it produces the spark that ignites the petrol/air mixture in the engine's cylinder. The spark plug can have a dramatic effect on the performance of the engine, it must therefore be checked on a regular basis to maintain the performance of the engine.

Below are some hints on the correct replacement procedure for spark plugs:

1. Identify which spark plug lead fits which cylinder. A suggestion is to attach numbered tags to the respective leads if no other identification is available
2. Pull the connectors off the plugs. Do not pull on the cable.
3. Ensure that the spark plug spanner is securely fitted before attempting to remove the plug. Care must be taken not to crack the ceramic insulator.
4. Set the gap on the new plugs to the manufacturer's specification, consult the owner's manual.
5. Fit the new plugs and tighten to finger tight.
6. Using a spark plug spanner of the correct size, tighten the plugs between ½ and ¾ of a turn from finger tight. Refer to the owner's manual for torque specifications.
7. Fit the plug connectors in the correct firing sequence and ensure they are securely attached to the plugs.
8. Start the engine. If it does not run smoothly, repeat step 1 to 7 and check that the plugs have not been damaged during tightening. Check ignition leads and replace if necessary, also check for cracked insulators, air gap etc.

Plug Wrench Troubles

Care must be taken on installation that the plug wrench does not slant or slip causing insulator breakage.

Look for the following qualities in a wrench

1. It must fit the plug hexagon properly.
2. The inner space must be large enough to avoid contact with the insulator.
3. The socket must completely cover the hexagon.
4. A hexagon socket wrench is less likely to slip than a twelve point type.

Important of Heat Range

As the amount of the thermal load applied to the spark plug depends on the model of the engine and operating conditions, various heat grades of plugs are required. HOT TYPE: A hot running plug to maintain the insulator nose at a temperature high enough to burn off oil and carbon deposits, providing a long heat flow path for the dissipation of heat. COLD TYPE: A cold running plug to avoid pre-ignition and burning out of the firing end, providing a short heat flow path to permit faster heat dissipation.

Consult the owner's manual or plug suppliers for the correct plug specification for your vehicle.

USED SPARK PLUG APPEARANCE - CAUSE AND REMEDIES:

1. NORMAL:

• The core nose is lightly coated with grey-brown deposits.
• Electrodes are not burning unduly - gap growth is about 0.003mm per 1000 kilometers.
• Plugs are ideally suited to engine.
• Service at about 10 000 to 15 000 kilometers.
• Replace at about 20 000 kilometers.

2. CARBON FOULED - Matt black and sooty.

Symptoms:

• Hard starting
• Misfiring
• Black exhaust smoke

Causes:

• Rich mixture
• Retarded ignition
• Low compression
• Too cold a spark plug
• Clogged air cleaner
• Faulty choke

Remedy:

• Check float level
• Check choke
• Check ignition timing
• Check air cleaner
• Check compression
• Replace spark plug with correct heat range

3. OIL FOULED - Wet black in colour

Symptoms:

• Hard starting
• Misfiring
• Grey-white exhaust smoke
• Loss of oil

Causes:

• Worn rings
• Worn Pistons
• Leaking valve stem seals and guides
• Over-filled oil sump

Remedy:

• Replace worn components
• Replace spark plugs with correct heat range

4. LEAD FOULDED - Yellowish green

Symptoms:

• Misfiring or hesitation under acceleration, load or cruising

Causes:

• Fuel with high lead contact
• Incorrect fuel grade used
• Sticking ignition advance

Remedy:

• Check for sticking distributor advance
• Use lower octane fuel
• Lean off slow speed fuel mixture
• Use spark plugs one heat range warmer

5. OVERHEATED - Light grey

Symptoms:

• "Pinking" under acceleration or climbing hills
• Engine runs on, after being switched off

Cause:

• Lean mixture
• Advanced ignition
• Use of fuel with insufficient octane rating
• Too hot a spark plug

Remedy:

• Check float level
• Check jets are not clogged
• Check ignition timing
• Replace spark plugs with correct heat range

6. OVERHEATED - Light grey - melted

Symptoms:

• "Pinking" under acceleration or climbing hills
• Engine runs on after being switched off

Causes:

• Serious overheating
• Lean Mixture
• Advanced ignition
• Use of fuel with insufficient octane rating
• Too hot a spark

Remedy:

• Take corrective measures urgently before engine damage occurs
• Check float level
• Check jets are not clogged
• Check ignition timing
• Replace spark plugs with correct heat range

7. HEAVY DEPOSITS

Symptoms :

• Hard Starting
• Reduced fuel economy

Causes :

• Fuel or oil additives
• Excessive upper cylinder lubricant
• Worn valve guides
• Normal electrode wear

Remedy:

• Replace worn parts
• Replace spark plugs with correct heat range

8. SPLIT CORE NOSE

Symptoms:

• "Pinking" under acceleration or climbing hills
• Engine runs on after being switched off

Causes :

• Lean mixture
• Advanced ignition
• Inlet manifold leaks
• Cooling system problems
• Incorrect gap-setting techniques
• Use of fuel with insufficient octane rating

Remedy:

• Check ignition timing
• Replace spark plugs

Midas Motor Parts Centers Recommend CHAMPION or NGK SPARK PLUGS

INDEMNITY
Remember this is for information only, for more details consult the workshop manual for your vehicle.