Specifications

PART 1-1-GENERAL ENGINE SERVICE
1-15
Tool-RC-500
FIG. 23—Cleaning Ring Grooves
INSPECTION
Carefully inspect the pistons for
fractures at the ring lands, skirts,
and pin bosses, and for scuffed,
rough, or scored skirts. If the lower
inner portion of the ring grooves
have high steps, replace the piston.
The step will interfere with ring
operation and cause excessive ring
side clearance.
Spongy, eroded areas near the
edge of the top of the piston are
usually caused by detonation, or
pre-ignition. A shiny surface on the
thrust surface of the piston, offset
from the centerline between the pis-
ton pin holes, can be caused by a
bent connecting rod. Replace pis-
tons that show signs of excessive
wear, wavy ring lands, fractures,
and/or damage from detonation or
pre-ignition.
Check the piston to cylinder bore
clearance with a tension scale and
ribbon, following the procedure un-
der "Fitting Pistons." Check the ring
side clearance following the proce-
dure under "Fitting Piston Rings."
Replace piston pins showing signs
of fracture or etching and/or wear.
Check the piston pin fit in the piston
and rod.
Replace all rings that are scored,
chipped, or cracked. Check the end
gap and side clearance. It is good
practice to always install new rings
when overhauling the engine. Rings
should not be transferred from one
piston to another regardless of
mileage.
REPAIRS
Fitting Pistons. Pistons are avail-
able for service in standard sizes and
0.020, 0.030, 0.040, and 0.060-inch
oversize.
If the clearance is greater than the
maximum limit, recheck calculations
to be sure that the proper size piston
has been selected, check for a dam-
aged piston, then try a new piston.
If the clearance is less than the
4'/
4
5
POUNDS
(EXAMPLE)
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POU
PULL
IN
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GAUGE
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— .002
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— .001
V
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-0+ .001
CLEARANCE IN
.0008"
(EXAMPLE)
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.002
INCHES
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(EXA
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.003
26"
MPLE)
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RIBBON
RIBBON-
RIBBON
RIBBON
RIBBON .
RIBBON
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.004
V
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4
POUNDS
-(EXAMPLE)
.005
A1017-A
FIG. 24-Piston Clearance Chart
minimum limit, recheck calculations
before trying another piston. If none
can be fitted, refinish the cylinder for
the next size piston.
When a piston has been fitted,
mark it for assembly in the cylinder
to which it was fitted.
If the taper and out-of-round
conditions of the cylinder bore are
within limits, new piston rings will
give satisfactory service provided
the piston clearance in the cylinder
bore is within limits. If the new
rings are to be installed in a used
cylinder that has not been re-
finished, remove the cylinder wall
"glaze."
To fit a piston:
1. Calculate the size piston to be
used by taking a cylinder bore check
(Fig. 30).
2. Select the proper size piston to
provide the desired clearance.
3. Make sure the piston and cyl-
inder block are at room temperature
(70°F). After any refinishing opera-
tion, allow the cylinder bore to cool
and make sure the piston and bore
are clean and dry before the piston
fit is checked.
4. Attach a tension scale to the
end of a feeler gauge ribbon that is
free of dents or burrs. The feeler
ribbon should be Vi-inch wide and
of one of the thicknesses listed in
Fig. 24.
5. Position the ribbon in the cyl-
inder bore so that it extends the
entire length of the piston at 90°
from the piston pin location.
6. Invert the piston and install it
in the bore so that the end of the
piston is about \Vi inches below the
top of the cylinder block and the
piston pin is parallel to the crank-
shaft axis.
7. Hold the piston and slowly pull
the scale in a straight line with the
ribbon, noting the pull required to
remove the feeler ribbon (Fig. 25).
In Fig. 24, the diagonal lines rep-
resent feeler ribbons of various thick-
nesses, the horizontal lines represent
the pounds pull, and the vertical lines
represent the clearances. To deter-
mine the clearance, locate the line
representing the pounds pull required
to remove the feeler ribbon from the
cylinder bore. Follow the horizontal
line to the right until it intersects the
diagonal line representing the feeler
ribbon. Read down the vertical line
for the clearance.
Example 1. If a 0.0015-inch feeler
ribbon is used and it takes approxi-
mately AVA -pounds pull to remove
the feeler ribbon, the clearance is ap-
proximately 0.0008 inch. This is de-
termined by locating the pounds pull
(4V4) in Fig. 24 and following the
line to the right until it intersects
with the diagonal line representing
the 0.0015-inch feeler ribbon. Read
down the vertical line for the clear-
ance (approximately 0.0008 inch).