Onan T260G Service Manual page 47

A.
Measure and record as "A" the cylinder bore
diameter (parallel to crankshaft) near the top
of cylinder bore where greatest amount of
wear occurs.
B. Also measure and record as "B" cylinder bore
diameter (parallel to crankshaft) at the bottom
of piston travel.
C. Measure and record as "C" cylinder bore
diameter (perpendicular to crankshaft) near
the top of cylinder bore where greatest
amount of wear occurs.
D. Also measure and record as "D" cylinder bore
diameter (perpendicular to crankshaft) at the
bottom of piston travel.
E. Reading "A" subtracted from reading "B" and
reading "C" subtracted from reading "D"
indicates cylinder taper.
If cylinder taper exceeds that specified in
DIMENSIONS AND CLEARANCES rebore and
hone cylinder to the next oversize.
F. Reading "A" compared to reading "C" and
reading
"B"
compared to reading "D" indicate
whether or not cylinder is out of round. If out of
round exceeds that specified in DIMENSIONS
AND CLEARANCES the cylinders must be
rebored and honed to the next oversize. A
reboring machine is used when going to oversize
pistons.
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. Final
bore diameter should equal the standard diameter
added to the oversize.
TOP END OF CYLlNDER
WEAR
RING
A REA
0 4 9 0
I
BOTTOM OF
RING TRAVEL
I
FIGURE
18.
METHODS OF MEASURING THE DIAMETER
OF A CYLINDER BORE
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:
lf boring
bar is
operated incorrectly
1. Make, sure cutting tool is properly ground before CAUTION
it will produce a rough cylinder sur- using it.
face that may not clean up even when honed. Boring
should be done only by qualified service personnel
2.
Be sure top of engine block is smooth and deposit
who are careful in their work. free.
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