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2.
Measure the piston 1/4-inch above the
bottom of the piston skirt from front to back.
Fig. 4-82
I
l
A049
3.
Subtract the piston skirt measurement (step
2) from the cylinder bore measurement (step
1). The difference must fall between the
values listed in the chart. If the difference
exceeds the values listed, the problem must
be corrected before the engine is assembled.
II
NOTE: If
the cylinder bore is within toler-
ance, but the clearance exceeds the maxi-
mum value for the engine, the piston must be
replaced. When replacing a piston, a new piston
pin and needle bearing must also be installed.
Acceptable Piston
Wear Limit
Skirt/Cylinder Clearance
Clearance
Engine
(mm) (In.)
(mm)
(in.)
AB25F1/F2
0.05- 0.0020-
Up to 0.15 Up to 0.006
0.06 0.0025
AA28F2/F3
0.04- 0.0015-
Up to 0.15 Up to 0.006
0.06 0.0025
AA34F3
0.04- 0.0015-
Up to 0.15 Up to 0.006
0.06 0.0020
AC44A3
0.05- 0.0020-
UptoO.15 Up to 0.006
0.06 0.0025
AB50A3
005- 00020-
UptoO.15 Up to 0.006
0.06 0.0020
AC50F2
0.05- 0.0020-
UptoO.15 Up to 0.006
0.06 0.0025
AE50A2
0.05- 0.0020-
Up to 0.15 Up to 0.006
0.06 0.0025
Check Piston Ring End Gap
1.
Remove carbon buildup from the piston
rings.
2.
Insert the piston ring approximately 3/8-inch
into the top of the cylinder bore. Position the
ring horizontally in cylinder by pressing the
dome of the piston against the ring.
3.
Slide a feeler gauge between the ends of the
ring. Piston ring end gap is listed below for
either all new components or for acceptable
wear limits.
Fig. 4-83
A057
4.
Since the amount of wear at the ends and
center of the piston ring arc affects the end
gap, replace the ring set if the ring gap is
excessive. If new rings are installed, cylin-
ders should be deglazed with a cylinder
hone. Use 500 or 600 grit stones on a hone
with honing oil for lubrication.
ACCEPTABLE RING END GAP CLEARANCES
New Components
Engine
Clearance (mm) Clearance (in.)
AB25F1/F2
0.20-0.40
0.008-0.016
AA28F2/F3
0.15-0.36
0.006-0.014
AA34F3
0.15-0.36
0.006-0.014
AC44A3
0.15-0.36
0.006-0.014
AB50A3
0.20-0.40
0.008-0.016
AC50F2
0.20-0.40
0.006-0.014
AE50A2
0.15-0.36
0.006-0.014
Wear Limit
AB25F1/F2
0.20-0.83
0.008-0.033
AA28F2/F3
0.15-0.80
0.006-0.031
AA34F3
0.15-0.80
0.006-0.031
AC44A3
0.15-0.80
0.006-0.031
AB50A3
0.20-0.83
0.008-0.033
AC50F2
0.20-0.83
0.008-0.033
AE50A2
0.20-0.83
0.008-0.033
Check Piston Pin Diameter
1.
Clean the piston pin of any lubricant or
coating.
41
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