Onan T260G Service Manual page 48

3. 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.
4.
Make an initial rough cut, followed by a finish cut.
Then hone cylinder bore to the specified oversize.
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 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
lubricants 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 to 450
rpm) 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 complete.
Do not use a solvent or gasoline since they wash
oil from the walls but leave the metal particles.
8 . Dry crankcase and coat it with oil.
Deglazing Cylinder Bores
Deglaze the cylinder bores if there are no scuff marks
and no wear Or out of round beyond specifications
before installing new rings. Deglazing gives a
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
bristle tips to produce a crosshatch pattern in the
cylinder bore.
3. Use a slow speed drill to drive the deglazing tool.
Move deglazing
tool
up and down in cylinder (10 to
12 complete strokes) rapidly enough to obtain a
crosshatch pattern (Figure 19).
FIGURE 19. CROSS HATCHING
...
Never use gasoline or commer-
CAUTION
cial cleaners to clean cylinder
bores after deglazing or honing. These solvents
will not remove abrasives from the 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.