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VO LVO
103270
Fig
. 2-24.
Marking on
pistons
and cylinde
r
bl ock
PISTONS,
PISTON RINGS
AND GUDGEON PINS
Measuring the pistons
The p
ist,
o ns are me awred
wi,
t
h
a micromef'er at rig ht
angl
l
'es to t he g
udg
e
on
p
in
ho le
2.5
mm
(.098")
from
t he I'ower edge o
n th
e p
isto
n ma'rked
71 /4
on the
crow
n face. O
n
late prod. pisto ns marked
71/9
t he
correspondin
g me
a
sure ment is
12
mm
(0,47").
Fit of pistons in cylinders
The fit
of the
pistons
in
their respective cylinders is
tested
without
the piston rings being
iii,
t ted
.
The
c1ear-
ance
at
right angle'S to the gudgeen pin
hole
is
measured with afeeler ga-uge
1/2"
wide and
.03
mm
(.0012")
thick 'attached
I
t O a spring balance. The force
appl'ied
shoul,d be
1
kg
(2.2
Ib.).
This ,gives the aver-
age value for
pis~on
c1earance. When the
above-
menr
t ioned force isapplied, the
pis-
t on
c1earance ob-
tained
is
equal to
~he
thi'
c kness of the
I
f eeler gauge
used
.
Feeler gauges
which
are
.02
mm
(.0008")
or
.04
mm
(.0016")
thick can,
there~ore,
ClIlso be
u'
s
ed.
The
test is carried out at several
diffe re
nt
de
pths.
Standard bore
cyl'
i
nde,
r s
have
a
-
lette
r sJtamped on
which
shows the
dimen'
s ions, and th
e
pistons
conce
rn-
ed
shou,ld
be marked wi1h the 'so-me
,letter.
Piston ring fit
IN A NEW OR RE-BORED CYLINDER
1.
Push down the piston rings oneafter another in
the
cyl,inder
bore. Use a reversed piston to ensure
tha.f the rings comeinTo the correct position.
2.
Measure the ring gap with a feel
e
r gauge. The
gap shoul,d be
AO-
.55
mm
(.016-.022").
If
neces-
sary, the gap can be increased with the help of
a special fi:le
.
3.
Check the piston rings in
,
t heir respe'Ctive grooves
roHing then
in
the
groove
. Al so measure the
Fig. 2-25.
Fitting the piston
1. Fitting ring SYO
2823
c1ea:rance ot a few points. See "Specifications" for
measurements.
IN A
W
ORN CYLINDER
BOR E
When
checking
the
fit
in
a
worn
cylinder hore, the
rings must
be checked
'
at the
botrtom
dead centre
position where
the diameter of
the bore is
smallest.
Assembling and fitting the piston
and connecting rod
When assembling, make sure tha-t the piston is turned
aorrectly so thart" the sloft on
top
of the piston faces
forwards as shown
in
Fiig.
2-24.
If
the piston is turned
the
wrong way,
thi,
s
will
cause a ,Ioud
noise.
The
nu.mber
marking on
,
t he conneotrng red
shou,ld
be
turned to face away kom the cam shaft side. The
gu-
dgeon pin
is
then fitted, tthe
cirdip
placed
in
posi-
tion and the
pi'
s ton rings fitted
.
Use
pisten ring g'rips when
fi~ing
the rings. The
compression rings are marked "TOP" and the
upper
'
r
ing on each piston
is
cromed.
P-
Iaee
the bearing
sheiis in position.
Turn the rings so tha.t the g,aps do
not
come directly
under
one
another.
Then
lubricate
the piston and
bearing surfaces.
Use
firfting ring SVO
2832
see
Fig.
2-25,
when fitting
the piston
in
the cyHnder
bore. T,ig
hten
the
conilecting
2:
13
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