Transcript Presentation - Spark plugs

Spark Plugs
Topics covered in this presentation:
 Spark Plug Construction
 Spark Plug Reach, Seating and Heat Range
 Spark Plug Servicing
Spark Plugs
The Spark Plug
The spark plug:
Terminal
 Ignites the air and fuel mixture.
Ribbed insulator
 Removes heat from the
combustion chamber.
Typical spark plug components:
Shell
Conductive seal
Centre electrode
Insulator nose
Ground electrode
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Spark Plugs
The Steel Shell
The shell is threaded so it can be
screwed into the cylinder head.
Hex
It is machined with a hexagonal
section, for plug removal and fitting.
To minimize corrosion, its surface
is electroplated with nickel.
Thread
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Spark Plugs
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.
Spark Plugs
The Ceramic Insulator
Purpose:
 To prevent high voltages
from shorting to ground.
Ribs
 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.
Nose
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Spark Plugs
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
Spark Plugs
Ground and Centre Electrodes
Electrodes are made from
nickel alloy or platinum.
They must be resistant to high
temperatures and corrosion.
Ground
electrode
Centre
electrode
The ground electrode
is welded to the shell.
The centre electrode
has a machined tip.
Spark
erosion
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Spark Plugs
Question 3
In a spark plug, what is the ground electrode connected to?
A) Shell
B) Ceramic insulator
C) Centre electrode
D) Insulator nose
Spark Plugs
Spark Plug Dimensions
Thread Diameter
Spark Plugs are made in
10, 12, 14, and 18 mm
thread diameters.
Spark Gap
Reach
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.
Spark gap
Thread diameter
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Spark Plugs
Question 4
Spark plugs are made in four different thread diameters.
Is this true or false?
Answer True or False.
Spark Plugs
Spark Plug Dimensions
Spark Plug Reach
Incorrect reach can cause
engine running problems
or spark plug damage.
Cylinder
head
Too
short
Too
long
Correct
reach
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Spark Plugs
Spark Plug Seating
Flat Seating
Conical
Seating
No
Spark
washer
plugsrequired
must beas
fitted
plugwith
is a metal washer
sealed
to seal by
combustion
its conicalchamber
seat. and remove heat.
Metal
No washer
washer
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Spark Plugs
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.
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Spark Plugs
Question 5
What temperature, in degrees C, would be within the ideal range
of operation?
Enter your answer and press SEND.
Spark Plugs
Heat Dissipation
2%
The combustion process produces heat.
Dissipation occurs as follows:
 20% is absorbed by
intake stroke fresh air.
 58% is absorbed by the
cylinder head walls.
 20% is absorbed by the insulator
and spark plug side walls.
 2% is absorbed by
spark plug wires.
10%
10%
58%
20%
Fresh air
100%
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Spark Plugs
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%
Spark Plugs
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
Insulator nose length = distance
from tip of insulator to where it
meets the metal shell.
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Spark Plugs
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.
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Spark Plugs
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.
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Spark Plugs
Resistor Spark Plugs
Spark plug with carbon compound
resistor in centre core.
Plug with
carbon resistor
The resistor suppresses radio
frequency interference (RFI).
Resistance
material
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Spark Plugs
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
Spark Plugs
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.
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Spark Plugs
Spark Plug Conditions
Normal use
Carbon fouled
Overheated
Deposit fouled
Gap bridged
Splashed deposits
Cracked insulation
Oil fouled
Pre-ignition
Glazed deposits
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Spark Plugs
Question 8
What is this spark plug suffering from?
A) Carbon fouled
B) Glazed deposits
C) Gap bridges
D) Oil fouled
Spark Plugs
Spark Plug Gap Adjustment
Typical Procedure:
 Obtain gap information
from shop manual.
Feeler
gauge
 Check gap between electrodes
with a feeler gauge.
 It should be a sliding fit.
Tool to
alter gap
 If necessary, adjust gap
using feeler gauge tool.
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Spark Plugs
Question 9
What device is normally used to measure the spark plug gap?
A) Micrometer
B) Ruler
C) Feeler gauge
D) Microscope
Spark Plugs
Spark Plug Fitting
Typical Procedure:
 Apply grease
to spark plug
threads.
 Hand screw
spark plugs into
cylinder head.
90°
Flat seat
 Tighten plugs as
per shop manual.
15°
 Refit spark
plug leads.
Conical seat
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Spark Plugs
Summary
You should now be aware of:
 Spark Plug Construction
 Spark Plug Reach, Seating and Heat Range
 Spark Plug Servicing
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