
4/23/97
3 - 43
ENGINE
REPAIR
This detonation shockwave
“hammerin
”
of the piston
inside the c
linder causes dama
e to piston crown
C
,
top rin
and
roove
F
, piston side skirts
E
, and pin
locks
D
.
The followin
is a list of possible causes for detonation:
1. Lean fuel mixture.
2. Low octane fuel.
3. Advanced ignition timing.
4. Engine lugging.
5. Buildup of carbon deposits on piston or cylinder
head, causing excessive compression.
6. Wrong cylinder head or excessive milling of head
increasing compression ratio.
PRE-IGNITION—
Pre-i
nition is the i
nitin
of the fuel-air mixture prior to
proper i
nition spark. Pre-i
nition causes internal
shock, resultin
in pin
s, vibration, and power loss.
Severe dama
e is caused to the piston crown
A
,
rin
s, and valves results from pre-i
nition.
Check the followin
for causes of pre-i
nition:
1. Hot internal carbon deposits.
2. Incorrect spark plug (high heat range).
3. Broken ceramic insulation of spark plug.
4. Hot sharp edges on valves.
IMPROPER ROD AND PISTON ALIGNMENT—
Check rod and piston ali
nment when piston shows a
dia
onal wear pattern
A
extendin
across the skirt of
the piston. Contact with the c
linder wall shows on
bottom of skirt at left and rin
lands on the ri
ht
B
.
CYLINDER BORED IMPROPERLY—
A c
linder bored at an an
le to the crankshaft ma
result in improper rin
contact with the c
linder which
ma
cause the followin
:
1. Rapid and uneven piston ring wear.
2. Rapid and uneven piston wear.
3. Loose or broken piston pin retaining rings.
4. Excessive oil consumption.
A broken piston pin retainin
rin
caused the dama
e
A
shown. Piston pin retainin
rin
s loosen or break
due to:
1. Rod misalignment.
2. Excessive crankshaft end play.
3. Crankshaft journal taper.
4. Weak piston pin retaining rings.
5. Incorrectly installed piston pin retaining rings.
Inertia can also cause a broken piston pin retainin
rin
to beat out the piston and c
linder, causin
extensive
dama
e.
M29947
D
C
F
E
M30039
A
A
M29948
B
M29949
A
Installing clutch spring, need a diagram.
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Stx38 hydro need manual plz.
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