Service and Parts Manual - Cummins Onan

FIGURE 33. MEASURING PISTON CLEARANCE
1. Fitting Pistons:
a. Proper piston tolerances must. be maintained
for satisfactory operation.
b. Measure the piston to cylinder clearance as
shown in Figure 33 to be sure the total clearance
follows specifications.
2. Fitting Piston Rings:
a. Install the piston ring in the cylinder bore.
Invert the piston and push the ring to the end
of ring travel, about halfway into the bore,
which trues the ring end gap. Check the gap
with a feeler gauge as shown in Figure 34.
b. The practice of filing ring ends to increase the
end gap is not recommended. If the ring end
gap does not meet specifications, check for the
correct set of rings and the carrect bore size.
A cylinder bore that is 0.001 ” under size will
reduce the end gap 0.003 ” .
FIGURE 34. POSITIONING OF PISTON RING AND
MEASURING OF END GAP
L
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CYLINDER BLOCK
1. Make a thorough check for cracks. Minute cracks
may be detected by ccating the suspected area
with a mixture of 25% kerasene and 75% light motor
oil. Wipe the part dry and immediately apply a
coating of zinc oxide (white lead) dissolved in
wood alcohol. If cracks are present, the white
coating will become discolored at the defective
area.
2. Inspect the cylinder bore far scaring. Check the
Welsh plugs for a tight, even fit and the fins for
breakage.
3. Check the cylinder bore for taper, out of round
and wear, with’a cylinder bore gauge, telescope
gauge or inside micrometer (Figure 35). These
measurements should be taken at four pIaces - the
top and bottom of piston ring travel.
4. Record measurements taken lengthwise at the top
and bottom of ‘the piston travel as follows:
a. Lengthwise of the black, measure and record
as “A” the diameter of the cylinder at the top
of the cylinder where greatest ring wear occurs.
b. Also, lengthwise of the blak, measure and
record as “By’ the cylinder diameter at the
piston skirt travel.
c. Crosswise of the block, measure and record
as “C” the diameter of the top of the cylinder
at the greatest point of wear.
d.’Measure and recard as “D” the diameter at
the bottom of the cylinder bore and crosswise
of the block.
e. Reading “A” compared to reading “B” and
reading “C” compared to reading “D’? indicates
cylinder taper.