~-----------------,---_TUE
ENGINE
A
suitable,
the
correct working clearance having been
allowed In
the
grading operation.
The
piston
size
should
therefore
correspond
with
the
marking
on
the
top
face
of
the
cylinder
block
on
the
right-hand side. which Indicates
the
actual size of each
cylinder bore.
The bores and pIstons
are
graded in four sizes
:-
Bores of nominal size
±-ooo
In. to
+·()()()49
In.
marked .. STD ..
Bores of nominal size +·0005 In. to +·00099
in.
marked
+·0005
Bores of nominal size +·0010 In. to +·00149 In.
marked
+·0010
Bores of nominal size +,0015 In.
to
+·00199 In.
marked
+·0015
The
piston clearance Is
-0011
In. minimum to ·0029In.
maximum
(oOS6
mrn,
to
·073 mrn.], measured at
the
top
of
the
skirt, Immediately below
the
oil control ring, and
across
the
thrust
faces, l.e. at 90
Q
to
the
gudgoon pin
axis. This is Important as
the
piston skirt Is tapered
and oval. and
the
clearance can only be measured In
this one position.
To facilitate correct measurement of the bores and
pistons,
the
actual sizes of
the
various gradlngs
are
given In
the
table below.
The
markings on
the
top
face of
the
cylinder block
will Indicate these sizes clearly.
Oversize bores on reconditioned engines supplied
under
the
M.G. reconditioned engine scheme
are
limited to
two
oversi:z:es
:-
+·020 In, graded In 4 sizes as
the
standard grading
+tQ40
"
tl
n U
The actual sizes of these pistons and bores
are
prcvlded In
the
following table
:-
Pisto n Mark] ng
Suiuble
for Bore SI:te
In. mm.
STANDARD
PISTON
SIZES
To
suit
It
STD .. bore
2·6181
~66'500~
2·6185
66·510
Production engInes wIth bores
To
suit
+·0005
bore
2·6186
~66-513)
-(102
In. oversll:e
or
over
~re
made
Into
+·010
In.
bores
and
graded
2-6190 66·523)
in t.he same st.eps as
the
standard
To suit
+·0010
bore
2·6191
(66-525)
bore engInes.
2-6195 (66·535)
To
suit
+·0015
bore
2·6196 (66-538)
2-6200
(66'S48)
Plswn Marking
Suiuble
fer
Bore
Size
In. mm.
To
suit
+·0200
bore
2·6381
~67.008)
2-6385 67-018)
To suIt +0(1205
bore
206]86
~67.021
)
OVERSiZE
PISTON
SIZES
206390
67,031)
+·010
In.
RANGE
TQ
sult
+.0210
bore
206m
~67'033)
2-6395
67'043)
To
sult
+·0215
bore
2-6396
(67'046~
2·6400 (67·0S6
Pmon
Marking
Suluble
for Bore SIze
in.
mm.
To
suit
+-0400
bore
HSSI
(67·516)
2·6585
(67-526)
OVERSIZE
PISTON
SIZES
To
suit
+00405
bore
206586
~67'S29~
+-040
In. RANGE
2-6590 67-539
To
suIt
+-0410
bor.
206591
~67-S41
~
2·6595 67-551
To
suit
+·0415
bore
206596
1
67
.
554
)
2·6600
67'5604)
Note.-
The
later-type
pistons
have oval and
tapered
skins. and
considerable
care must be
exercised
when
making measurements.
M.G.
Midget.
tssue"
(1-1
" E) 91826--2,'55
AI3
Wishvilles Classic
Automobile Library
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