Topics covered in this presentation: Spark Plug Construction

1. Topics covered in this presentation: • Spark Plug Construction • Spark Plug Reach, Seating and Heat Range • Spark Plug Servicing

2. Terminal Ribbed insulator Shell Conductive seal Centre electrode Insulator nose Ground electrode The Spark Plug The spark plug: • Ignites the air and fuel mixture. • Removes heat from the combustion chamber. Typical spark plug components: Next >

3. Hex Thread The Steel Shell The shell is threaded so it can be screwed into the cylinder head. It is machined with a hexagonal section, for plug removal and fitting. To minimize corrosion, its surface is electroplated with nickel. Next >

4. Question 1 How many sides does a spark plug have on the part designed for plug removal and replacement? Enter your answer and press SEND.

5. Ribs Nose The Ceramic Insulator Purpose: • To prevent high voltages from shorting to ground. • To remove heat from the combustion chamber. It is made from aluminium oxide and glazed to discourage dirt. Ribs increase the surface area of the insulator to reduce flashover to ground. Next >

6. Question 2 What material is the spark plug's ceramic insulator made from? A) Aluminium nitrate B) Aluminium hydroxide C) Aluminium oxide D) Aluminium carbonate

7. Ground electrode Centre electrode Spark erosion Ground and Centre Electrodes Electrodes are made from nickel alloy or platinum. They must be resistant to high temperatures and corrosion. The ground electrode is welded to the shell. The centre electrode has a machined tip. Next >

8. Question 3 In a spark plug, what is the ground electrode connected to? A) Shell B) Ceramic insulator C) Centre electrode D) Insulator nose

9. Reach Spark gap Thread diameter Spark Plug Dimensions Thread Diameter Spark Plugs are made in 10, 12, 14, and 18 mm thread diameters. Spark Gap The gap must be correct. If it is too small, a weak spark is produced. If it is too large, the mixture will burn inefficiently. Next >

10. Question 4 Spark plugs are made in four different thread diameters. Is this true or false? Answer True or False.

11. Cylinder head Too short Correctreach Too long Spark Plug Dimensions Spark Plug Reach Incorrect reach can cause engine running problems or spark plug damage. Next >

12. Metal washer No washer Spark Plug Seating Flat Seating Conical Seating No washer required as plug is sealed by its conical seat. Spark plugs must be fitted with a metal washer to seal combustion chamber and remove heat. Next >

13. Spark Plug Temperature Ideal spark plug tip temperature = 500 to 850°C. If temperature = low, carbon and combustion chamber deposits will not be burnt off. If temperature = high, the plug may overheat, damaging the electrodes. Next >

14. Question 5 What temperature, in degrees C, would be within the ideal range of operation? Enter your answer and press SEND.

15. Fresh air 100% Heat Dissipation 2% The combustion process produces heat. Dissipation occurs as follows: • 20% is absorbed by intake stroke fresh air. 10% • 58% is absorbed by the cylinder head walls. 10% • 20% is absorbed by the insulator and spark plug side walls. 58% • 2% is absorbed by spark plug wires. 20% Next >

16. Question 6 Approximately what percentage of heat from the combustion process is absorbed by the cylinder head walls? A) 2% B) 20% C) 25% D) 58%

17. Insulator nose length Spark Plug Heat Range Heat range = spark plug's ability to remove combustion chamber heat. Determined by: • Insulator nose length. • Gas volume around the insulator nose. • Composition of the insulator and the centre electrode. Insulator nose length = distance from tip of insulator to where it meets the metal shell. Next >

18. Spark Plug Heat Range Hot Plug: • Long insulator nose, exposing a large surface area to combustion gases. • Dissipates heat slowly. • Firing end heats up quickly. Cold Plug: • Shorter insulator nose, minimizing surface area exposed to combustion gases. • Dissipates heat quickly. • Firing end heats up slower. Next >

19. Other Types of Spark Plugs Some spark plugs have multiple ground electrodes. They provide multiple spark paths which reduces spark erosion. This surface discharge plug can be used with CDI systems. It provides good sparking, even when fouled. Next >

20. Plug with carbon resistor Resistance material Resistor Spark Plugs Spark plug with carbon compound resistor in centre core. The resistor suppresses radio frequency interference (RFI). Next >

21. Question 7 What can be incorporated into a spark plug to suppress radio frequency interference? A) Ferrite beads B) Wire wound resistor C) Capacitor D) Carbon resistor

22. Spark Plug Removal Typical Procedure: • Remove the lead from each plug, by using the rubber boot. • Slacken each spark plug. • Use an air line/brush to remove all debris from around each plug. • Remove all plugs and place on bench in cylinder order. • Inspect each spark plug. Next >

23. Carbon fouled Normal use Overheated Deposit fouled Splashed deposits Gap bridged Oil fouled Cracked insulation Glazed deposits Pre-ignition Spark Plug Conditions Next >

24. Question 8 What is this spark plug suffering from? A) Carbon fouled B) Glazed deposits C) Gap bridges D) Oil fouled

25. Feeler gauge Tool to alter gap Spark Plug Gap Adjustment Typical Procedure: • Obtain gap information from shop manual. • Check gap between electrodes with a feeler gauge. • It should be a sliding fit. • If necessary, adjust gap using feeler gauge tool. Next >

26. Question 9 What device is normally used to measure the spark plug gap? A) Micrometer B) Ruler C) Feeler gauge D) Microscope

27. 90° 15° Spark Plug Fitting Typical Procedure: • Apply grease to spark plug threads. • Hand screw spark plugs into cylinder head. Flat seat • Tighten plugs as per shop manual. • Refit spark plug leads. Conical seat Next >

28. Summary You should now be aware of: • Spark Plug Construction • Spark Plug Reach, Seating and Heat Range • Spark Plug Servicing End >