Once the lead is clean, check for burns,
cracks and other damage. Do not bend the
lead sharply, because the conductor might
break.
4 Inspect the remaining spark plug (HT)
leads, ensuring that each is securely fastened
at the distributor cap and spark plug when the
check is complete. If any sign of arcing,
severe connector corrosion, burns, cracks or
other damage is noticed, obtain new spark
plug (HT) leads, renewing them as a set.
5 Spring back the retaining clips or undo the
two screws and remove the distributor cap.
Thoroughly clean it inside and out with a dry
lint-free rag.
6 Examine the HT lead segments inside the
cap. If they appear badly burned or pitted
renew the cap. Also check the carbon brush
in the centre of the cap, ensuring that it is free
to move and stands proud of its holder. Make
sure that there are no signs of cracks or black
“tracking” lines running down the inside of the
cap, which will also mean renewal if evident.
7 Inspect the rotor arm checking it for
security and also for signs of deterioration as
described above.
8 Refit the distributor cap on completion.
33 Spark plug renewal
1
1 It is vital for the correct running, full
performance and proper economy of the
engine that the spark plugs perform with
maximum efficiency. The most important
factor in ensuring this, is that the plugs fitted
are appropriate for the engine (a suitable type
is specified at the end of this Chapter). If this
type is used and the engine is in good
condition, the spark plugs should not need
attention between scheduled renewal
intervals. Spark plug cleaning is rarely
necessary, and should not be attempted
unless specialised equipment is available, as
damage can easily be caused to the firing
ends.
2 Spark plug removal and refitting requires a
spark plug socket, with an extension which
can be turned by a ratchet handle or similar.
This socket is lined with a rubber sleeve, to
protect the porcelain insulator of the spark
plug, and to hold the plug while you insert it
into the spark plug hole. You will also need a
wire-type feeler gauge, to check and adjust
the spark plug electrode gap, and a torque
wrench to tighten the new plugs to the
specified torque.
3 To remove the spark plugs, open the
bonnet, where fitted, release the three plastic
retaining lugs and lift the ignition shield off the
front of the engine
4 If the marks on the original-equipment HT
leads cannot be seen, mark the leads 1 to 4,
to correspond to the cylinder the lead serves.
5 Pull the leads from the plugs by gripping
the rubber boot, not the lead, otherwise the
lead connection may be fractured (see
illustration).
6 Unscrew the spark plugs, ensuring that the
socket is kept in alignment with each plug - if
the socket is forcibly moved to either side, the
porcelain top of the plug may be broken off. If
any undue difficulty is encountered when
unscrewing any of the spark plugs, carefully
check the cylinder head threads and sealing
surfaces for signs of wear, excessive
corrosion or damage; if any of these
conditions is found, seek the advice of a
dealer as to the best method of repair.
7 As each plug is removed, examine it as
follows - this will give a good indication of the
condition of the engine. If the insulator nose of
the spark plug is clean and white, with no
deposits, this is indicative of a weak mixture.
8 If the tip and insulator nose are covered
with hard black-looking deposits, then this is
indicative that the mixture is too rich. Should
the plug be black and oily, then it is likely that
the engine is fairly worn, as well as the mixture
being too rich.
9 If the insulator nose is covered with light tan
to greyish-brown deposits, then the mixture is
correct, and it is likely that the engine is in
good condition.
10 The spark plug electrode gap is of
considerable importance as, if it is too large or
too small, the size of the spark and its
efficiency will be seriously impaired. The gap
should be set to the value given in the
Specifications.
11 To set the electrode gap, measure the
gap with a feeler blade or adjusting tool, and
then bend open, or closed, the outer plug
electrode until the correct gap is achieved
(see illustration). The centre electrode should
never be bent, as this may crack the insulation
and cause plug failure, if nothing worse. If the
outer electrode is not exactly over the centre
electrode, bend it gently to align them.
12 Before fitting the spark plugs, check that
the threaded connector sleeves at the top of
the plugs are tight, and that the plug exterior
surfaces and threads are clean (see Haynes
Hint).
13 On installing the spark plugs, first check
that the cylinder head thread and sealing
surface are as clean as possible; use a clean
rag wrapped around a paintbrush to wipe
clean the sealing surface. Ensure that the
spark plug threads are clean and dry then
screw them in by hand where possible. Take
extra care to enter the plug threads correctly.
14 When each spark plug is started correctly
on its threads, screw it down until it just seats
lightly, then tighten it to the specified torque
wrench setting.
15 Reconnect the HT leads in their correct
order, using a twisting motion on the boot
until it is firmly seated. Finally, refit the ignition
shield.
Every 12 000 miles or 12 months 1•19
1
33.5 Pull the leads off the spark plugs by
gripping the rubber boot
33.11 Adjusting a spark plug electrode
gap
It is very often difficult to insert spark
plugs into their holes without cross-
threading them. To avoid this
possibility, fit a short length of 5/16 inch
internal diameter rubber hose over the
end of the spark plug. The flexible hose
acts as a universal joint to help align
the plug with the plug hole. Should the
plug begin to cross-thread, the hose
will slip on the spark plug, preventing
thread damage to the aluminium
cylinder head
If new spark plug leads are
to be fitted, remove the
leads one at a time and fit
each new lead in exactly the
same position as the old one.
To Next Page
Loading...