F. Reading
“A”
compared to reading “C” and
reading “B” compared to reading “D” indi-
cates whether or not cylinder is out-of-round.
If out-of-round exceeds0.003 inch
(0.08
mm),
the cylinders must be rebored and honed to
the next oversize. A reboring machine is used
when going to oversize pistons. The following
repair data covers honing to oversize by use
of a hone.
Reboring
the
Cylinder
Rebore and hone engine whenever cylinder bore is
worn, damaged, out-of-round, or if cylinder taper
exceeds specifications.
A
worn cylinder bore should
be resized to the smallest standard oversize diameter
at which
it
will clean up. The final finish and bore
diameters should then be obtained by honing.
/BCAUTIONI
If boring bar
is
operated incorrecfly,
it will produce a rough cylinder sur-
face that may
not
clean up even when honed. Boring
should be done only by qualified service personnel
who are careful in fheir
work.
After boring to the correct oversize cylinder bore
dimension, piston and ring clearance should be
appropriate. There is no need to adjust or“fit” pistons
and rings.
When reboring cylinders, take the following pre-
cautions:
1.
2.
3.
4.
Make sure cutting tool is properly ground before
using it.
Be sure top of engine block is smooth and deposit
free.
Clean base of boring bar before bar is set up.
Deposits under boring bar will cause
it
to
tilt,
and
the cylinder will be distorted after boring.
Make
an
initial rough cut, followed bya finish cut.
Then hone cylinder bore to the specified over-
size.
Honing Cylinders [Using Precision Hones)
Refer
to
hone manufacturer’s recommended grit size
to produce specified surface finish of
20
to
40
RMS.
Too
rough of a finish will wear out the rings and too
smooth of a finish can retard piston ring seating.
1, Position block solidly for either vertical or horiz-
ontal honing.
Use
either
a
drill press
or
heavy-
duty drill which operates at approximately
250
to
450
r/min.
2.
Follow hone manufacturer’s instructions for the
use of oil or lubricant on stones.
Do
not use lubri-
cants with a dry hone.
3.
Insert hone in bore and adjust stones to fit snugly
to the narrowest section. When adjusted cor-
rectly, the hone should not shake or chatter in
cylinder bore but will drag freely up and down
when hone is not running.
4.
Connect drill to hone and start drill. Feel out bore
for high spots, which cause an increased drag on
stones. Move hone up and down
in
bore with
short overlapping strokes about
40
times per
minute. Usually bottom of cylinder must be
worked out first because
it
is smaller.
As
cylinder
takes a uniform diameter, move hone up and
down all the way through cylinder bore.
5.
Check diameter of the cylinder regularly during
honing. A dial bore gauge is the easiest method,
but a telescoping gauge can be used. Check size
at six places in bore; measure twice at top, middle
and bottom at 90-degree angles.
6.
Crosshatch formed by the stones should form an
included angle of
23
degrees. This can be
achieved by moving the rotating hone (250 to450
r/min) up and down in cylinder bore about
40
times per minute.
7.
Clean cylinder bores thoroughly with soap,
water, and clean rags. A clean white rag should
not become soiled on wall after cleaning is com-
plete. Do not use a solvent or gasoline, since they
wash
oil
from the walls but leave metal particles.
?
8.
Dry crankcase and coat
it
with oil.
Deglazing Cylinder
Bores
Deglaze the cylinder bores if thereare no scuff marks
and no wear or out of round beyond specifications
before installing new rings. Deglazing gives a fine
finish but does not enlarge cylinder diameter,
so
the
original pistons with new rings may still be used.
The reason for deglazing a cylinder is to provide
cavities to hold oil during piston ring break-in.
1.
Wipe cylinder bores with a clean cloth which has
been dipped in clean, light engine oil.
2.
Use a brush type deglazing tool with coated bris-
tle tips to produce a crosshatch pattern in the
cylinder bore.
3. The deglazing tool should be driven by a slow
speed drill. Move deglazing tool up and down
in
cylinder
(10
to
12
complete strokes) rapidly
enough to obtain a crosshatch pattern as shown
in Figure 9-30.
-1
Never use gasoline
or
commer-
cial cleaners
to
clean cylinder
bores
after deglazing
or
honing. These solvents
will not remove abrasives from fhe walls. Abra-
sives
not
removed from engine will rapidly wear
rings, cylinder walls, and bearing surfaces
of
all
lubricated parts.
4.
Clean cylinder bore thoroughly with soap, water,
and clean rags. Continue cleaning until a clean
white rag shows no discoloring when wiped
through cylinder bore.
b
9-1
4
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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