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TM 10-3930-653-14&P
(2) BORING AND HONING
(1) Determine proper oversize according to extent of
cylinder bore wear, measure outside diameter of piston
(long span across skirt of piston) and rebore, leaving
0.02 mm (0.0008 in) for honing, so that piston to cylinder
clearance is within 0.025 to 0.045 mm *0.0010 to 0.00 1
8 in). Measure cylinder at normal temperature. If
reboring of one cylinder, is required, rebore all cylinders
at same time.
Fig. 4-52. Measuring Long Span of Piston Skirt
Fig. 4-53. Honing of Cylinder Block
(2) Calculating individual cylinder bore sizes:
Piston skirt outside diameter
(measured value): A
Piston to cylinder clearance: B
B
=
0.025 to 0.045 mm
(0.0010 to 0.0018 in)
[at 20°C (at 68° F)
Honing allowance: C
C
=
0.02 mm (0.0008 in)
Cylinder bore: D
D
=
A+ B-C
(3) Cylinder boring precautions
Cutting depth of cutting tool should be approximately
0.05 mm (0.0020 in). Do not cut quickly all at one time
cut gradually.
Measure cylinder bore carefully, since bore will
change due to heat generated by cutting.
To avoid deviations or distortions due to cutting heat,
bore cylinders in following sequence of 24-1-3.
Mark pistons according to applicable cylinder so that
pistons are properly applied to correct cylinder and so
that they are not interchanged (mixed).
(4) Measure bore and check taper and trueness (out-of-
round) condition after proper finishing by honing.
(5) Measure piston to cylinder clearance.
Fig. 4-54. Measuring Clearance between
Piston and Cylinder
For this measurement, Insert piston from reverse
side (with piston pin removed) and insert a feeler gauge
0.04 mm (0.016 in) so that it projects on thrust side of
piston. Then apply a spring scale to gauge and lift
vertically. If spring scale reading is 0.5 to 1.5 kg (1.1 to
3.3 lb), clearance is normal.
Oversized piston
Piston size
Diameter mm (in)
87.185 to 87.235
STD
(3.4325 to 3.4344)
87.655 to 87.715
0.50 O.S.
(3.4514 to 3.4533)
88.165 to 88.215
1.00 O.S.
(3.4711 to 3.4730)
88.665 to 88.715
1.50 O.S.
(3.4907 to 3.4927)
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