MG MGA Twin Cam Workshop Manual page 42

THE ENGINE
A
ensure this, muk the caps and connecting rods on their
sides which are .fitted together with the number of the
eylinder from which each was taken.
Dism•ntliec
Remove the
l\<O
cuclips securing each gudgeon pin
in its
J~Uton
and press the gudgeon pin out. Mark the
gcdgeon pins and pistons for reassembly to their original
positions and to their original connecting rods.
Check
the gudgeon pin and the connecting rod little-
end
bearings
for wear with the
dimension given in the
'GENERAL DAT A' section. If the bush is worn it should
be removed and
a new bush fitted. A light
press
is most
suitable for this operation.
Rf'1L.. -..mbl7
When pressing in the new bush ensure that the oil
hole in the bush is in line with the oil hole in the con-
n..:ling rod.
Replacement bushes must be finish-reamed to size
after pnessing into the connecting rod (sec the ' GENERAL
DATA' section for the correct dimensions). The piston
gudgeon pin bosses must not be reamed as oversize
gudgeon pins
are
not supplied.
Assemble the pistons to the connecting rods by inserting
the gudgeon pins, which should be
a
hard hand-push fit
at
a room temperature of
68" F. (20" C.).
Secure each
gudgeon pin in position with the two circlips, ensuring
that they fit weU into their grooves.
Replaeemaat
Replacement
of the piston and connecting rod is a
direct reversal of the above, but the piston ring gaps
should be set at
ISO"
to each other.
If
the piston rings have been remo,ed from the piston
they mu>t
boo
JC:placcd
a• duailed in Scc:tion A.28.
It
is essential
that the connecting rod and piston
~semblies
should be replaced in their own bores and
fitted the same way round, i.e. with the big-end cap
facing the half-speed shaft side of the engine.
Refit the big-end
bcarinp
in their original positions.
Section A.28
PISTON RL 'IGS
If no special piston ring expander is available use a
piece of thin steel such as a smoothly ground hacksaw
blade or a disus..-d ·020 in. (· SO mm.) feeler gauge.
Raise one end of the ring out of its groove. Insert the
steel strip between the ring and the piston. Rotate the
strip around the piston, applying slight upward pressure
to tbe raised portion of the ring until it rests on the land
MGA (Twin
Cam). !Jauc
4. J240J
above the ring grooves. It cao then be eased off the
piston.
Do not remove or replace the
rings
o,..,r tbe piston
skirt, but always ovu the top of the piston.
Before fitting new rings clean the grooves in the piston
to remove any carbon deposit. Care mun be taken not
to remove any metal or side-play between the ring and
the groove will result. with consequent e>tcessivc: oil
consumption and loss of gas-tightness.
When refitting the rings note that the second and third
compression rings are tapered and marked with the
letter
·r
(top) for correct reassembly.
New rings must be tested
in the cylinder bore to
ensure
that the ends do not butt together. The best way to do
this is to
insert the piston approximately I in. (2·54 em.)
mto the cyliodu bore and push the ring down onto the
top of the piston and hold it there in o rder to keep the
ring
square
with the bore. The correct ring
gap is «>8
to .013 in. (·20 to ·33
mm.).
[See Addendum for additional i nformati on. ]
Section A.29
HALF-SPEED
SHAFT
Removal
Disconnect the battery.
Drain the cooling system and remove the radiator as
detailed in Section
C .4.
Remove the water pump and by-pass pipe (Section
A.4),
the distributor drive gear and housing, nod the
camshaft covers. Remove tbe timing chain cover (Section
A .21)
and the timing chain
(Section A.22).
Draw off the timing chain driving sprocket with
a suit-
able drawer. Remove the sump, oil pump, and oil pump
drive shaft (see
Section A.JI).
Take out the three set screws and sbakeproof washers
which secure the half-speed shan locating plate and with-
draw the half-speed shaft. Note that shuns are fitted
behind the locating plate to control the half-speed sbal\
cnd-ftoaL
If
the balf-specd shaft bearing clearances
are
excessive
new bearings should be fitted. Ensure that the oil boles
in the bearings line up with the oil passages in the
cylinder block. The bearings must be reamed to give the
correct diametrical clearance (sec ' GENERAL DATA').
Replaeem<11t
R eplacement of the half-speed shaft is a reversal
of
tbe
above procedure. Adjust the half-speed sbaft end-float
if
necessary by increasing or decreasing tbe thickness of
the shims fitted behind the half-speed shan locating
plate. See ' GENERAL DATA' for the cor•·ect end-Ooat
measurement.
A.lS