MG MGA Twin Cam Workshop Manual page 54

THE IGNITION SYSTEM
B
(I) Battuy to starter switch termirud. Connect the volt·
meter to the starter switch terminal and to earth.
No reading indicates a faulty cable or loose con-
nections.
(2) Starter switch to control box terminal 'A' (brown
lead). Connect a voltmeter to the control box
terminal
'A'
and to earth. No reading indicates a
faulty cable or loose connections.
(3) Control box terminal 'Al'. Connect a voltmeter to
the control box terminal 'A I' and to earth. No
reading
indicates a fault in the series
winding
of
the control box.
(4) Control box termioal ' Al ' to terminal on igllition
switcb (brown 10·ith blue lead). Connect a voltmeter
to the ignition switch terminal and to eanh. No
reading indicates a faulty cable or loose con·
nections.
(S)
Ignition switch. Connect
a
voltmeter to the second
ignition switch terminal (white lead) and to eanh.
No reading indicates a fault in the ignition switch.
(6) Ignition s10·itch to fusebox terminal 'A3' (white lead).
Connect the voltmeter to the
fuse
box terminal • A3'
and to earth. No reading indicates a faulty cable
or loose connections.
(7)
Fosebox terminal 'A3' to ignition coil tenuinal 'SW'
(white lead). Connect a voltmeter to the ignition
coil terminal 'SW' and to earth . No reading
indicates a faulty cable or loose connections.
(8)
Ignition coil. Connect a voltmeter to the ignition
terminal 'CB' (white with black lead) and to earth.
No reading indicates a fault in the primary winding
of the coil and a new coil must be fitted.
(9)
Ignition coil to distributor (white with black lead).
Connect a voltmeter
to
the d istributor low-tens:on
terminal a nd to earth. No reading indicates a
faulty cable or loose connections.
Fig . B.l
The method of connecting H . T .
/~ads
MGA (Twio
cam).
I•S<Je 3. 32403
(10) Contact breaker and cap:u:itor. Connect the volt-
meter across the breaker points. No reading
indicates a fault in the capacitor.
Section
B.4
HIGH-TENSION CABLES
The high-tension cables must be examined carefully
and any which have the insulation cracked, perished, or
dama~d
in any way must
be
renewed.
To fit the cables to the terminal of the ignition co il
thread the knurled moulded terminal nut over the lead,
bare the end of the cable for about
i
in. (6 mm.), thread
the wire through the brass washer removed from the
original cable, and bend back the strands over the washer.
Finally, screw the terminal into the coil.
To make the connections to the terminals in the distri·
butor moulded cap, first remove the cap and slacken the
screws on the inside o f the mould. i ng till they are clear
of the cables. Cut the new cables off to the required
length, push th em completely home, and tighten tbe
securing screws.
The cables from the d istnl>uto r to the sparking plugs
must be connected up in the correct firing order, which
is I, 3, 4, 2. Secure them firmly
to
the connectors.
Section
B.S
CONI'ACf BREAKER
The distributor has a pre-tilted contact breaker uni t.
The moving contact breaJcer plate is balanced on two
nylon studs and the angle through which the plate may
be tilted is controlkd by
a
stud riveted to the moving
contact breaker plate locating in a slo t in the base plate.
The plate carrying the fixed contact is secured by one
screw only.
After tile firs t 500 miles (800 km.) a nd subsequently
every 6,000 miles (9600 km.) check the contact breaker
as follows:
( I) Rotate the crankshaft until the contact breaker
points are fully opened and check the gap witb a
gauge having a thickness of -QI4 to •016 in. (·35 to
·40 mm.). If the gap is correct the gauge s hould
be a sliding fit. Do not alter the setting unless the
gap varies considerably from the gauge thickness.
To adjust the setting keep the engine in the
position which gives maximum o pening o f the
contacts, then slacken the fixed contact plate
securing screw and adjust the contact gap by
inserting a screwdriver in the notched hole and
turning clockwise to reduce the gap and anti-
clockwise to increase it. Tighten the securing screw.
B.3