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Table of Contents
128 MAINTENANCE-ENGINE
NOTE: Abnormal wear such as a marked diagonal
pattern across the piston skirt may mean a bent
con-
necting rod or crankshaft.
Piston Diameter Measurement
Table H28
Piston Diameter
Standard
54.955-54.970 mm
E
E
V)
Service Limit
54.80
mm
Table H27 applies only to a cylinder that has
not
been
bored
to oversize, and
Table
H28 applies only to
the stan
dard
size piston. In
the
case of a rebored cyl-
inder and
oversize piston, the usable
range
for
the
cylinder is the diameter that the cylinder was
bored
to plus
0.1
mm
and the
service
limit for the piston
is
the oversize piston original diameter minus 0.15 mm.
If
the
exact
figure
for
the rebored
diameter is unknown,
it can be
roughly
determined by measuring the dia-
meter at the base of the cylinder.
NOTE: Whenever a piston or cylinder block has
been
replaced with a
new
one,
the
motorcycle must be
broken in,
the
same as with a new machine.
Piston/cylinder clearance
The
piston-to-cylinder
clearance
is
measured
whenever
a piston or the cylinder
block is
replaced
with a new one, or
whenever
a cylinder
is rebored
and
an
oversize piston
is
installed.
The
standard
piston-to-cylinder
clearance
must
be
adhered
to
whenever the cylinder block is replaced
or a
cylinder
reborer:l.
If only a piston
is rep laced, the clearance
may exceed the standard slightly.
But
it must
not
be
less
than
the
minimum,
ln
order
to
avoid piston
seizure.
The most accurate way to find the piston clearance
is
by
making separate piston and cylinder
diameter
measu
rem
en
ts
and
then
computing the difference
between the two
values.
Measure
the
piston diameter
as
just
described, and measure
the
cylinder
diameter
at
the
very bottom of the cylinder.
Table H29
Pistonl~ylinder Clearance
Standard
0.030~0.057 mm
Boring, honing
When boring and honing a cylinder, note the
following:
1.
Before boring a
cylinder,
first measure
the
exact
diameter of the
oversize
piston, and then,
in
accord-
ance
with the
standard clearance
given
in Table H28,
determine
the diameter
of
the rebore.
2. Cylinder inside diameter must not vary more than
0.006 mm at any
point.
3. There
are two sizes of oversize pistons available:
0.5 mm and
1.0
mm. Oversize pistons
require
over-
size
rings.
4. Be wary
of measu
remen
ts
taken immediately
after
boring since
the
heat affe.cts
cylinder
diameter.
Piston/cylinder seizure
Remove the cylinder
block
and pistons
to
check the
damage.
If
there
is
only slight damage, the
piston
may
be smoothed with
#400 emery
cloth, and any
aluminum
deposits removed
from
the cylinder with either #400
emery
cloth
or
light
honing.
However,
in
most
cases,
the cylinder
will
have to
be
bored to
oversize and
honed, and
an oversize piston
installed.
Piston cleaning
Built-up
carbon
on the piston head reduces the cool-
ing capability of
the
piston and
raises
compression,
lead ing to
overheating
wh
ich
could possibly even melt
the
top of the
piston.
To
decarbonize
the
piston
head,
remove the piston (Pg.
53), scrape
off the
carbon
,
and
then lightly
polish the piston with
fine emery
cloth.
· ·
(
H43)
Carbon accumulated
in
the
piston ring
grooves can
cause
th
e
rings
to
stick.
Remove the rings, and clean
ou
t
any
carbon
deposits using the end of a
broken
piston ring or some
other
suitable
tool.
(
H44)

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   Also See for Kawasaki Z250 1981

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Kz350 1981

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