Car Care

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Car Care Illustrated
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Simple servicing
All-round lubrication
Renewing oil and air filters
Simple spark plug servicing
Adjusting the engines timing
Adjusting valve clearance
Inefficient brakes improved
Adjusting the handbrake
Rear wheel bearing service
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Simple spark plug servicing
Spark plugs are among the most vital parts of the
ignition system. Their condition and adjustment
effect both performance and economy. Although
they look simple in construction they are
designed to work in direct contact with the
extreme temperatures and pressures inside the
engines combustion chambers. The constant
passage of electrical energy across the gap
between the two electrodes gradually erodes away
the metal. You should check and adjust your
spark plugs about every 10000 km. Spark plugs
need to be renewed about every 20000 km.
Step 1
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Simple spark plug servicing
Step 1
Assemble tools and components
You must have a plug spanner to unscrew the spark
plugs from the cylinder head. Most car makers
include one in the tool kit but special plug
spanners can be bought.
You can buy a combined set of feeler guages with
a gapping tool cheaply from most accessory shops.
Each feeler gauge has its thickness marked on
it. If the gapping tool does not include a
contact file you should buy one.
Step 2
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Simple spark plug servicing
Step 2
Remove spark plugs
Before pulling off the plug connector caps, label
each plug's high tension lead with its cylinder
number so that it can be replaced correctly.
Then pull of the plug caps - always pull the cap
itself, not the plug leads. Push the plug
spanner firmly on to the first plug and unsrew it
about four turns. Use the paint brush to clean
any dirt or flakes of corrosion from around the
plug hole to prevent them from falling inside the
cylinder when the plug is out. Some cars have a
particularly deep plug recess where a brush will
not go - either blow out the dirt or use a vacuum
cleaner to remove it. Unscrew the plug
completely and repeat the procedure for all other
plugs. Bear in mind that if the engine is still
hot, the plugs will be too. Look at the colour
and condition of the
tip of each spark plug. If the engine is well
tuned all the plugs should be the same light
biscuity brown colour. Plugs of a significantly
different appearance are a sign of a problem
needing further investigation. Marked rounding
of the centre electrode together with pitting of
the side of the electrode means that the plug
should be discarded. It is not a good idea to
renew just one plug - always fit a whole new set.
Step 3
Step 1
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Simple spark plug servicing
Step 3
Clean up plugs
Badly blackened spark plugs or those with harp
deposits can be cleaned by grit blasting never
use a wire brush on the tip of the plug because
the bristles can leave conductive tracks of metal
across the centre electrode insulator. Some
garages will grit blast plugs for a small charge
but compare their charge with the cost of new
plugs before you go ahead, because the saving
may be insignificant. There is also a DIY plug
cleaner that workd in the same way as the
professional machine.
A DIY blaster for cleaning plug tips
You can clean off any soft, dusty deposits with a
toothbrush. A wire brush can be used to remove
any dirt from the screw heads of the plug. Wipe
off any dust or oil on the ceramic insulator
body. Next, use the contact file to clean the
tip of the central electrode and the inside face
of the side electrode. If the file will not fit
between the electrodes, use the lever notch on
the gapping tool to bend back the side electrode.
File the surfaces of the electrodes until they
are clean and flat be carefull to keep the file
level while you are using it.
Using a wire brush to clean the threads
Step 4
Step 2
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Simple spark plug servicing
Step 4
Adjust plug gap
Most cars have a plug gap of about 0.6-0.7 mm,
but the gap recommended for your car should be
given in your manual. Pick the feeler gauge of
the correct thickness and use it to measure the
gap between the electrodes. The feeler gauge be
a tight sliding fit.
The feeler gauge should just slide in the gap
You can adjust the gap by bending the side
electrode. If the gap is to narrow, bend back
the side electrode with the lever notch on the
gapping tool. If the gap is too wide, tap the
side electrode gently with a spanner so that it
move closer to the central electrode. Always
check that new spark plugs have the right gap.
Adjusting the plug gap
Step 5
Step 3
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Simple spark plug servicing
Step 5
Replace spark plugs
A very light smear of engine oil on the plug
threads will make it easier to screw in and help
prevent them seizing up. However, plugs which
are too creasy can cause bad running so give the
insulators a final wipe before you screw them in.
Plugs should never be over tightened they must
only be screwed down hard enough to make a good
gas seal. Screw in each plug until you feel it
meet the seal. Before you reconnect the plug
heads, note the type of terminal connection on
the top of the
Smearing a little oil on the threads
Plug. There are two types. Some plug caps push
home directly on to the thin screw thread which
protrudes from the ceramic insulator, while
others fit over a much thicker adaptor collar
which screws on to the plug terminal. Push the
plug caps firmly home over the plug-top
terminals. Make sure you have the plug leads on
the right plugs.
Cleaning plugs before replacing them
Step 4
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