Coil; Sparking Plugs - MG MGA Twin Cam Workshop Manual

in the original position. When seen from above, the small offset of the driving dog must be
on the right and the driving slot for the rotor arm must be in the six o'clock position.
4. Adjust the contact breaker to give a maximum opening of .014 to .016 in. (.35 to .40
mm.).
B.11 COIL
The coil does not require any attention beyond seeing that the terminal connections and the coil
mounting bolts are tight, and that the exterior is kept clean and dry, particularly between the terminals.
B.12 SPARKING PLUGS
Inspect, clean, adjust, and renew sparking plugs at the recommended mileage intervals (see
"MAINTENANCE ATTENTION).
When sparking plugs are removed from the engine their gaskets should be removed with them and
replaced on the plugs, which should be placed in a suitable holder. It is advisable to identify each plug
with the number of the cylinder from which it was removed so that any faults revealed on examination
can be traced back to the cylinder concerned.
When examining the plugs place a new plug of the same type beside the others to afford a ready
comparison of the relative condition of the used plugs.
Examine for signs of oil fouling. This will be indicated by a wet, shiny, black deposit on the insulator.
This is caused by oil pumping due to worn cylinders and pistons or gummed-up or broken rings.
Under such conditions oil from the cylinder walls is forced up past the ring on the suction stroke of the
piston and is eventually deposited on the plugs.
A permanent remedy for this cannot be effected, the only cure being the fitting of a new piston and
rings, or in extreme cases a re-bore may be necessary.
Next examine the plugs for signs of petrol (gasoline) fouling. This is indicated by a dry, fluffy, black
deposit which is usually caused by over-rich carburation, although ignition system defects such as a
run-down battery, faulty distributor, coil or condenser defects, or a broken or worn-out cable may be
additional causes. If the plugs appear to be suitable for further use proceed to clean and test them.
First remove the plug gaskets and examine them for condition. A large proportion of the heat of the
plug is normally dissipated to the cylinder head through the gasket between the plug and the head.
Plugs not screwed down tightly can easily become overheated so that they operate out of their proper
heat range, producing pre-ignition, short plug life, and "pinking'. On the other hand, it is unnecessary
and unwise to tighten up the plugs too much. What is required is a reasonably good seal between the
plug and the cylinder head and the use of a torque Wrench is recommended to tighten the plugs to a
figure of 30 lb. ft. (4.15 kg. m.).
If the plugs require cleaning it is preferable to make use of a proper plug cleaner of the type
recommended by the plug manufacturers, and the makers instructions for using the cleaner should be
followed carefully.
Occasionally a blistered insulator or a badly burnt electrode may be noticed when examining the
plugs.
If the plug is of the type normally recommended for the engine and it was correctly installed (down
tightly on the gasket), this condition may have been brought about by a very lean mixture or an
overheated engine. There is, however, a possibility that a plug of another type is required, but as a
rule the recommended plug should be adhered to
After cleaning carefully, examine the plugs for cracked insulators and wear of the insulator nose due
to excessive previous cleaning. In such cases the plugs have passed their useful life, and new plugs
should be installed.
Examine the insulator for deposits underneath the side electrode which have possibly accumulated
and which act as a 'hot-spot" in service.
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