John Deere stx38 - Manual (Page 76)

3 - 44
4/23/97
REPAIR ENGINE
PISTON ASSEMBLY—
DISASSEMBLE
1. Remove compression rings (C) from piston (B)
using ring expander.
2. Remove rails (A).
3. Remove spacer (D).
4. Remove retaining rings (E) by prying at indent (H).
5. Use wooden dowel to remove pin (F) from piston
and connecting rod (G).
6. Inspect parts.
PISTON INSPECTION
1. Carefully remove piston rings.
IMPORTANT: Do not use caustic cleaners or wire
brush to clean aluminum piston. Piston damage
can result.
2. Clean piston. Inspect for scoring or fractures.
3. Clean carbon from grooves using ring groove tool
(A).
PISTON RING END GAP
MEASUREMENT
IMPORTANT: If new rings are to be installed,
deglaze cylinder so rings will seat properly. (See
Deglaze Cylinder Bore, later in this section.)
1. Use a clean or new piston to push piston
compression ring squarely into bore, to a point
where it normally runs.
2. Measure end gap (A).
3. Remove ring and file ends squarely until gap meets
specification. Rings with too large a gap must be
replaced. If one piston ring needs replaced, all
must be replaced as a set.
Piston Ring End Gap (New Bore)
(12.5, 13, 14 hp) . . . . 0.3—0.5 mm (0.012—0.020 in.)
(15 hp) . . . . . . . . . . . . 0.27—0.51 mm (0.010—0.020)
Piston Ring End Gap (Used Bore) (Max)
(12.5, 13, 14 hp, 15hp) . . . . . . . . 0.77 mm (0.030 in.)
PISTON RING SIDE CLEARANCE
1. Measure piston ring side clearance (A) as shown at
several points around piston.
2. Replace piston if measurements exceed clearance
specifications.
Piston Ring-To-Groove Side Clearance
Top Compression Ring
(12.5, 13, 14 hp)
. . . . . . . . . . . . . . 0.040—0.105 mm (0.002—0.004 in.)
(15 hp) . . . . . . . . 0.060—0.105 mm (0.002—0.004 in.)
A
D
B
M55894
C
H
M55878
F
G
E
A
M29946
M52110
A
M52111
A