Reboring the Cylinder
Rebore and hone the 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 diameter should then
be
obtained by honing.
Final bore diameter should equal the standard di-
ameter added to the oversize.
CAUTION
improper boring will result in
engine
damage.
Boring
must
be
done by
qualified
mechanics.
After boring to the correct oversize cylinder bore di-
mension, piston and ring clearance should be ap-
propriate. There is no need to adjust to "fit" piston
and rings.
When reboring cylinder, take the following precau-
tions:
1.
Make sure the cutting tool is properly ground
before using
it.
2. Be sure the top of engine block is smooth and
deposit free.
3. Clean the base of the boring bar before bar is
set up. Deposits under the boring bar will cause
it to tilt and the cylinder
will
be
distorted after
boring.
4.
Make an initial rough cut, followed by a finish
cut. Then hone the cylinder bore to the speci-
fied oversize.
Honing Cylinder (Using Precision Hones)
1.
Position block solidly for either vertical or hori-
zontal honing. Use either a drill press
or
heavy-
duty drill which operates at approximately
250
to
450
rpm.
2.
Follow hone manufacturer's instructions for the
use
of oil or lubricant on stones.
Do
not use lu-
bricants with a dry hone.
3.
Insert hone in bore and adjust stones to fit
snugly to the narrowest section. When ad-
justed correctly, the hone should not shake
or
chatter in cylinder bore, but will drag freely up
and down when hone is not .running.
4.
Connect the drill to the hone and
start
drill. Feel
out
the bore for high spots, which cause an in-
creased drag on stones. Move hone up and
down in bore with short overlapping strokes
about
40
times per minute. Usually the bottom
of'
cylinder
must be worked out first because
it
is smaller. As the cylinder takes a uniform
diameter, move the hone up and down all the
way through cylinder bore.
5.
Check the 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
to
450
rpm) up and down in cylinder bore about
40 times
per
minute.
7.
Clean cylinder bore thoroughly with soap,
water and clean rags.
A
clean white rag should
Refer to hone manufacturer's recommended grit
not become soiled on wall after cleaning is
size to produce specified surface finish of
20
to
complete.
Do
not use a solvent or gasoline
40
RMS. Too rough
of
a finish will wear out the rings
since they wash oil from the walls but leave the
and too smooth of a finish can retard piston ring
metal particles.
seating.
8.
Dry
crankcase and coat it with oil.
11-17
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