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SECTION 10
INSPECTION AND RECONDITIONING
CYLINDER BARRELS
Inspection and Reconditioning
Check all gasket surfaces to make sure they are free
of gasket fragments.
Gasket surfaces must also be
free of deep scratches or nicks.
Scoring of the Cylinder Wall: Unbumed fuel, in severe
cases, can cause scuffing and scoring of the cylinder
wall. As raw fuel seeps down the cylinder wall, it
washes the necessary lubricating oils off the piston
and cylinder wall so that the piston rings make metal
to metal contact with the wall. Scoring of the cylinder
wall can also be caused by localized hot spots result-
ing from blocked cooling fins or from inadequate or
contaminated lubrication.
If the cylinder bore is badly scored, excessively wom,
tapered, or out of round, resizing is necessary.
Use
an inside micrometer to determine amount of wear
(refer to *Specifications, Tolerances, and Special
Torque Values", Section 1), then select the nearest
suitable oversize of either .003", .010", .020" or .030".
Resizing to one of these oversizes will allow usage of
the available oversize piston and ring assemblies.
Initially, resize using a boring bar, then use the follow-
ing procedures for honing the cylinder:
Honing
While most commercially available cylinder hones can
be used with either portable drills or drill presses, the
use of a low speed drill press is preferred as it facili-
tates more accurate alignment of the bore in relation
to the crankshaft crossbore.
Honing is best accom-
plished at a drill speed of about 250 RPM and 60
strokes per minute.
After installing coarse stones In
hone, proceed as follows:
1. Lower hone into bore and after centering, adjust
so that the stones are in contact with the cylinder
wall. Use of a commercial cutting-cooling agent
is recommended.
2. With the lower edge of each stone positioned
even with the lowest edge of the bore, start drill
and honing process.
Move hone up and down
while resizing to prevent formation of cutting
ridges. Check size frequently.
10.2
NOTE:
Keep in mind the temperatures caused by
honing may cause inaccurate measure-
ments. Make sure the barrel is cool when
measuring.
3. When bore is within .0025" of desired size, re-
move coarse stones and replace with burnishing
stones. Continue with bumishing stones until
within .0005" of desired size and then use finish
stones (220-280 grit) and polish to final size. A
crosshatch should be observed if honing is done
correctly. The crosshatch should intersect at ap-
proximately 23-33? off the horizontal. Too flat of
an angle could cause the rings to skip and wear
excessively, too steep of an angle will result in
high oil consumption (refer to Figure 10-2).
Figure 10-2. Cylinder Bore Crosshatch After Honing.
4. After resizing, check the bore for roundness, taper,
and size, Use an inside micrometer, telescoping
gauge, or bore gauge to take measurements (Re-
fer to Figure 10-3). The measurements should be
taken at three locations in the cylinder--at the top,
middle, and bottom. Two measurements should
be taken (perpendicular to each other} at each of
the three locations.
NOTE:
Your final bore size should be exactly
-003, .010, .020, or .030 over standard
size. Service replacement pistons are
manufactured to precise tolerances to
match those sizes.
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