MG MGA Twin Cam Workshop Manual page 76

THE FUEL SYSTEM
D
(2)
Fit the impact washer in the recess of tbe armature.
(3)
Screw the armature into position .
(4) Place the II guide rollers in position around the
armature.
Do not use
jointing
compoaDCI oa
the
d.iapbragm.
(5) Hold the magnet assembly in the left hand in an
approximately horizontal position.
(6) Screw the armature inwards until the 'throw-
over' ceases to
opera te, and then screw it baclc
gradually, a sixth of a turn (or one ho le) at a time,
a nd press tbe
;trm;tt\lre
in
after each part
of a turn
until it is found that when it is pushed in slowly
and firmly the 'throw-over' mechanism operates.
UBSCrew the armature a further two-thirds of a
turn
(four of the six holes). When a new diaphragm is
fitted it is probable that considerable pressure will
be required to push the armature right home.
(7)
Place t he cast-iron body in pos ition on the main
body, taking ca re to see that the drain hole in the
cast-iron body is at the bottom and all the rollers
arc still in their correct positions.
If a roller d rops out of position it w ill get
trapped between the two ports, and this will cut
a hole in the d iaphragm.
Make sure that t he east-iron body is seating
properly o n the maio body and insert the six
securing screws. Before tightening the screi'I'S down
it is essential that the diaphragm should
be
stretched
to its outermost position.
This may be done by inserting a matchstick
behind one of the white fibre rollers on t he outer
rocker, thus holding the points in contact (after first
repositioning the spring blade into its normal
position). If a current is then passed through the
pump the magnet will be energized and will pull
the armature and diaphragm forward, and while
it is in th is position the six screws should be
tightened. Altho ugh the diaphragnt-stre tching
o peration can
be
effected by the matchstick
method, a special tool for this p urpose is a\·ailable
from the S. U. Carburetter Co. or their Distributors.
The tool is a steel wedge, to be inserted under the
trunnion in the centre of the inner rocker in order
to stretch the diaphragm to its outermost position
before tightening the six fla nge screws.
(8) Finally, check t ha t when the spring blade is in its
normal position the clearance hole in it is so
positioned around the locking screw that each
contact point, according to t he operation of the
outer rocker, "ipes m·er the centr.-.llne of tbe other
contact
point and that this action is not to one
side of the centre on either contact. The width of
the gap at the points is approximately ·030 in.
(·76
min.).
(9) The pump should now be placed on test, using
a cut-away cover to enable the contact breaker
action to be observed and at the same time to
prevent the rocker hinge p in from falling out.
A test rig of the type illustrated in Fig. D.4 is advised;
either petrol (gasoline) or paraffin (kerosene) may be
used for testing purposes. Test figures are given in
'GEI'< "ERAL DATA'.
The usc of a glass tube and rubber
co nnections between the s ump and the test tank is
advised. When tbe pump is switched on it should prime
itself promptly, a nd t he paraffin , which is norm ally used
for testing, should rise in the glass container until it
flows over the top of the pipe having the
,~
in . (4 mm.)
hole drilled in it 2 in . (5 em.) below the top of the pipe.
If the o utput of the pump is not up to normal the
:&
in.
(4 mm.) diameter hole will
be
able to deal with all the
paraffin pumped and the liquid will not ftow over the top
of tbe pipe:. If a time-test
is
used. 1·5 pints (·9 litre) o f fuel pc:r
minute should be pumped.
FORKED
W!:DC~
7854.C
Fig. D.3
17re use of a forked w~dge to k eep the amJature
i11
the correct position for filling the diaphragm
These test rigs can be o btained complete from the
Service Parts Department of the S. U. Carhurelter Co.
or their Distributors.
Th is, therefore, constitutes a simple form of flow-
meter which establishes in a simple manner whether the
pump is giving a sufficient o utput or not. If there is any
D.1