John-deere stx38 User Manual Page 75

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4/23/97
3 - 43
ENGINE
REPAIR
This detonation shockwave
(
“hammerin
g
)
of the piston
inside the c
y
linder causes dama
g
e to piston crown
(
C
)
,
top rin
g
and
g
roove
(
F
)
, piston side skirts
(
E
)
, and pin
locks
(
D
)
.
The followin
g
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
g
nition is the i
g
nitin
g
of the fuel-air mixture prior to
proper i
g
nition spark. Pre-i
g
nition causes internal
shock, resultin
g
in pin
g
s, vibration, and power loss.
Severe dama
g
e is caused to the piston crown
(
A
)
,
rin
g
s, and valves results from pre-i
g
nition.
Check the followin
g
for causes of pre-i
g
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
g
nment when piston shows a
dia
g
onal wear pattern
(
A
)
extendin
g
across the skirt of
the piston. Contact with the c
y
linder wall shows on
bottom of skirt at left and rin
g
lands on the ri
g
ht
(
B
)
.
CYLINDER BORED IMPROPERLY—
A c
y
linder bored at an an
g
le to the crankshaft ma
y
result in improper rin
g
contact with the c
y
linder which
ma
y
cause the followin
g
:
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
g
rin
g
caused the dama
g
e
(
A
)
shown. Piston pin retainin
g
rin
g
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
g
rin
g
to beat out the piston and c
y
linder, causin
g
extensive
dama
g
e.
M29947
D
C
F
E
M30039
A
A
M29948
B
M29949
A
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Comments to this Manuals

Alicia Cross 12 Jul 2025 | 21:17:32

Installing clutch spring, need a diagram.

Fred 15 Aug 2025 | 02:18:54

Great

John Jaeger 06 Jan 2026 | 22:35:47

Stx38 hydro need manual plz.

James Smith 03 Apr 2026 | 23:03:46

The

GUILLAUME MILLOT 08 Apr 2026 | 19:44:25

Good