JO
MEASURE CLEARANCE HERE
FIGURE 27. MEASURING PISTON CLEARANCE
3. Fitting Pistons:
a. Proper piston tolerances must be maintained
for satisfactory operation.
b. Measure the piston to cylinder clearance as
shown in Figure 27 to be sure the total
clearanc^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 28.
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 correct bore size. A
cylinder bore that is 0.001 inch under size will
reduce the end gap 0.003
inch.
FIGURE 28. POSITIONING OF PISTON RING AND
MEASURING OF END GAP
CYLINDER
BLOCK
1.
Make a thorough check for cracks. Minute cracks
may be detected by coating the suspected area
with a mixture of 25 percent kerosene and 75
percent 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.
3.
Inspect the cylinder bore for scoring. Check the
Welsh plugs for a tight, even fit and the fins for
breakage.
Check the cylinder bore for taper, out of round
and wear, with a cylinder bore gauge, telescope
gauge or inside micrometer (Figure 29). These
measurements should be taken at four places -
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 block, 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 block, measure and
record as "B" 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 record 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.
30
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