CYLINDER
WALL
vv
CT-1062
FIGURE
9-22.
NEW RING IN WORN RING GROOVE
Improper width rings or excessive ring side clearance
can result in ring breakage. New rings in worn ring
grooves don't have good cylinder wall contact (Fig-
ure
9-22).
Replace pistons showing signs of scuffing, scoring,
worn ring lands, fractures or damage from pre-
gnition.
Connecting
Rod
Inspection:
Replace connecting rod
bolts and nuts with damaged threads. Replace con-
necting rods with deep nicks, signs of fractures,
scored bores or bores out
of
round more than
0.002
inch
(0.05
mm)
Use a new piston pin to check connecting rod for
wear.
A
push
fit
clearance is required and varies from
engine to engine.
If
a new piston pin falls through a
dry rod pin bore as a result
of
its own weight, replace
the rod or bushing as required.
Pisfon
Pin Inspection:
Replace piston pins that are
cracked, scored, or out
of
round more than
0.002
inch
(0.05
mm).
Bearing Inspection:
Inspect bearings for burrs,
breaks, pitting and wear. Replace bearing inserts that
are scored, have the overlay wiped out, show fatigue
failure, or are badly scratched. If bearings appear to
be serviceable, check them for proper clearance.
Piston Clearance
Proper piston tolerances must be maintained for
satisfactory operation. Use a micrometer to measure
the piston diameter at the point shown in Figure9-23.
When the cylinder bore
is
measured (see Cylinder
Block in this section), subtract the piston diameter
from the cylinder bore diameter to obtain the piston
to cylinder wall clearance. Refer to Dimensions and
Clearances in Section
3
for the recommended piston
clearance.
Fitting Piston Rings
Before installing new rings on the piston, check the
CT-1063
FIGURE
9-23.
PISTON CLEARANCE MEASUREMENT
ring gap by placing each ring squarely in its cylinder,
at a position corresponding to the bottom
of
its travel
(Figure9-24).Thegap between theendsofthe ring is
given in Dimensions and Clearances in Section 3.
The practice of filing ring ends to increase the end
gap is not recommended. If the ring end gap does not
meet specifications, check for the correctness of ring
and bore sizes.
A
cylinder bore that is
0.001
inch
(0.03
mm)
undersize will reduce the end gap 0.003 inch
(0.08
mm).
Standard size rings may be used on
0.005
inch (0.13
mm) oversize pistons. Rings that are
0.010,
0.020,
0.030 and
0.040
inch
(0.25,
0.51,
0.76
and
1.02
mm)
oversize are to be used on corresponding oversize
pistons. Rings
of
the tapered type are usually marked
TOP
on one side, or identified in some other manner.
Install these rings with the identification mark toward
the closed end of the piston.
PISTON
RING
IN
CYLINDER
BORE
FEELER
GAGE
CT-1064
FIGURE
9-24.
CHECKING RING
GAP
9-1
0
Redistribution or publication of this document
by any means, is strictly prohibited.
Redistribution or publication of this document
by any means, is strictly prohibited.
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