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20
Engine
Tr
actors,
Lawn
and
Garden
- 110
and
11
2
15-8
Piston,
Crankshaft
and
Flywheel
-
Kohle
r
SM-2059-(Apr-67)
PISTON
ANALYSIS-Continued
"
,,,
' ,
F
ig.
17-Hole
Burned
in
Piston
Caused
by
Pre-Igni
tion
Pre-ignition
is
the
ignitin
g of
the
fuel-air
mixture
prior
to
the
regular
ignition
spark.
Pre-i
g
nition
causes
severe
internal
shock
re-
sulting
in
pings,
vibration,
detonation
and
power
loss.
Severe
damage
to
piston,
rin
gs
and
valves
results
from
pre-ignition.
Wilen
pre-i
g
nition
is
suspected
and
detected.
check
and
correct
the
followin
g
possible
causes:
1.
Internal
carbon
depOSits
which
remain
incandesc
ent.
2.
Incorr
ec
t
spa
rk
plug
(high
heat
ran
g·e)
.
3.
Broken
ceramic
in
spark
plug.
4.
Sharp
edges
on
valv
es
or
elsewhere
in
the
combustion
chamber.
, I
J>
••
Fig
.
18-Diagonal
P i
ston
Wear
Palf
In Caused by
Bent
or
TWI
s
ted
C Ol1l1CCt ln Rod
Check
rod
and
piston
alignment
when
a
piston
shows
a
diagonal
wear
patt
e
rn
extending
across
the
skirt
of
th
e
piston.
Contact
with
cylinder
wall
shows
on
bottom
of
skirt
at
left
and
ring
lands
on
the
right.
A
cylinder
bored
at
an
ang
le
to
the
crankshaft
co
uld
also
cause
improper
ring
contact
with
the
cylinder
wall.
This
condition
can
cause:
1.
Rapid
piston
wear.
2.
Uneven
piston
wear.
3.
Excessive
oil
consumption
.
Lith
o
in
U
.S.A
.