MG MGA Twin Cam Workshop Manual page 192

R
THE CHASSIS
prepared and hand-surfaced wiU be suitable. The car
may then be directly c hecked by comparative measure-
ments, or a centre-lone dropped down from t. h e front a nd
rear centre of the frame and parallel track lines laid out.
From these lind the squareness of the car may easily
be checked.
Section R.3
A TWISTED FRAME
Checking the alignment of the frame
bare
is relati,·ely
a simple matter. especially if the frame can be set up on
a
large flat surface or face plate.
It
involves establishing
a datum or cenu-c-linc, from which all measurements can
be: token. Diagonals ar<:. chc. c kcd from suitable
Ji.~t:U
locating points, which can
be
cross-checked at the centre-
line on "hicb the d1agonal> should cross. as detailed in
chassis dimt-nsional drawing Fig. R. I. The llng.le of the
front cross-member >hould-·be 4• but may be gi>-rn an
allov.-ancc of
- 1
or
-o•.
Diagonal measurements
qu1clly determine "hich section of the frame is bent.
Accuracies of side-members are usually checked with
SUitable straight-edges. and squareness of side rails is
checked with straight-edge and square. Twist is checked
visually against straight..,dges laid transversely across the
frame at suitable points.
In the event of the frame being twisted. th1s condition
can be com:cted by anchoring the frame to a fixed
t~tle
and by usintt a s uitable lever or a stout beam of
timber. The frame can then be sprung back "ith effort
applied at the end of the lever.
If necess3f)', npply a well-spread heat at the twisted
section.
The frame being completely d ismantled.
11
is possible
to
~mo'c:
aU
sig.n~
of damat;e b) cuuiuts
vul lavlo
fu1
aettss in the inner ltner plates with the \\eldins torch.
hammering out bulges. dents, or bucUed areas, and
closing the holes by welding in the piece previously
.R.4
removed. The welds can
be
cleaned up and the repair is
then invisible.
When any adjustmenl to the frame is carried out do
not forget the light gauge of the material.
Final checking of the frame should be carried out in
accordance with the dimensions and diagonals indicated.
Comparative vertical measurements should reveal any
frame twist.
Check the wheel camber,
ca~tor
a ngle, king pin angle,
and front wheel alignment.
Section R.4
DIAGONAL FRAME C HECK
(Complete Car)
In checking the frame for distortion, diagonal measure-
ments may be takeo without removing tbe
body
from the
chassis by using a plumb-bob as follows.
Place the car
on a
level surface and block up the car
equally at each wheel approximatdy 12 in. (30 em.) high
with alltyres properly inflated.
Porform the measuring wi th accuracy and care.
Suspend the plumb-bob from various corresponding
points on the frame. such as indicated by the diagonal
Jines in Fig. R.I. The plumb-bob should be suspended
slightly above the floor. When the plumb-bob comes
to
rest marl: the floor dtrectly underneath
11.
The marks
made on the floor
will
represent various points of the
frame to be checked diagonally.
Measure the diagonal distance between the points;
this distance should agree within
t
to
i
in. (6·S
to 10 mm.).
Care must be taken to see that any two diagonals
compued represent uactly corresponding points on
each side of the frame.
Upon the result of this preliminary 111\CStJgahon a
dee1sion can be taken \\bet her the frame can
be
repaired
in position or l'hcth<r the frame must
be
stripped out
completely .