MG MGA Twin Cam Workshop Manual page 57

B
THE IGNITION SYSTE M
(3) Remove the nut and washer from the moving
contact anchor pio. Withdraw the insulating
sleeve from the capacitor lead and low-tension
lead connectors, noting the order in which they
are fitted. Lift the moving contact from the pivot
pin and remove the large insulating washer from
the anchor pin.
(4) Take out the screw, spring. and flat washer securing
the fixed contact plate and remove the plate.
(5) Remove the Stturing screw and the capacitor.
(6) Extract the two screws securing the base plate to
the distributor body, noting that one also secures
the earthing lead, and lift out the base plate.
Unhook the flexible actuating link connecting
the diaphragm in the vacuum unit with the moving
contact breaker plate.
IMPORT ANT.- Note the rl' l ative position of !be
rotor arm clriTe slot in the cam spindle and the
offset drive dog at the driring
end
of the spindle to
ensw-e that the timing is not 180•
out
when tbe cam
spindle
is
engaged with tbe eentrifogal weights
doring assembly.
(7) Take out the cam retaining screw and remove the
cam spindle.
(8) Take out the centrifugal weights. These may be
lifted out as two assemblies, each complete with
a spring and toggle.
(9) To release the suction advance unit remove the
circlip, adjusting nut, and spring. Withdraw the
unit. Take care not to lose the adjusting nut lock
spring clip.
(10) To release the spindle from the body dri>-e out
the parallel driving pin passing through the collar
o f the driving tongue member at the-lower end of
the spindle.
Section B.9
CAPACITOR
A ·2 microfarad metallized capacitor is fitted and the
eyelet on the cable connected to the contact breaker
terminal post is squared and slotted to prevent it twisting
round and short-circuiting against the distributor.
The best method of testing the capacitor is by substi-
tution. D isconnect the original capacitor and connect
a new one between the low-tension terminal of
the
distributor a. n d earth.
Section
B.to
REASSEMBLING THE DISTRIBUTOR
Reassembly is a direct reversal of the dismantling
procedure given in Section B.8, although careful
atten-
tion must be given to the following points.
8.6
( I) As they are assembled, the components of the aut~
matic advance mechanism, the distributor shaft, and
the portion of the shaft on which the cam fits must
be lubricated with thin, clean engine oil to Ref. D.
(2)
Tum the vacuum control adjusting nut until it is
in the half-way position when replacing the control
unit.
(3) When engaging the cam driving pins with the
centrifugal weights make sure that they are in
the original position. When seen from abo\-e, the
small offset of the driving dog must be on the
right and the driving slot for the · rotor ann must
be in the six o'clock position.
( 4) Adjust the contact breaker to give a maximum
opening of ·014 to --DI6 in. (·35 to ·40
mm.).
Section B.ll
COIL
The coil does not require any atten tion 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.
Section B.l2
S PARKING PLUGS
Inspect, clean, adjust, and renew sparking plugs at th<
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 cj·linder 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 tbe u sed plugs.
Examine for signs of oil fouling. This will be indicated
by a wet, shiny, black deposit on the
insulator. This
is
caused b y oil pumping due to worn cylinders and pistODS
or gummed-up or broken rings. U nder such conditions
oil from the cylinder walls is forced up past the rio&'
o n the suction stroke of the piston, and is eventually
deposited on the plugs.
A permanent remedy for this cannot be
effected, ~
only cure being the fitting o f a new piston and rings, or
in extreme cases a rebore may be necessary.
Next .,;amine the plugs for signs of petrol
(gasoline)
fouling. This is indicated by a dry, fluffy, black deposit
which
is
usually caused by over-rich carburatioD,
although ignition system defects such a s a run-down
MGA
(Twin
Cam).
Issue
3. Z1161