Normal Wear Pattern; Fitting Piston; Measuring Piston Ring Gap - Ford 1956 Truck Shop Manual

Section a-Cylinder Block, Pistons, Piston Rings, and Connecting Rods and Bearings
29
F;g. 44-Normal Wear Pattern
WEAR AREAS
6609
a bent connecting rod. The normal wear pattern of a
piston is shown in fig. 44.
Inspect the piston pins for signs of fracture or etch-
ing. Chec k the p in for proper fit in the piston and rod
bushing. Chec k for wear in the pin retainer grooves.
(2) REPAIRS.
Replace pistons showing signs of ex-
cessive skirt clearance, or ring side clearance, wavy ring
lands, frac tures or d a m age from detonation or pre-
ignitio n.
R eplace pist on pins showing signs of fracture or etch-
ing. Piston pins that show wear or
fit
loosely in the
piston or rod bushing should be replaced. R eplace all
piston pi n retainers.
(3) FITTING PISTONS. Pistons
of 0.020, 0.030,
0.040, 0.060 inch oversize are avai lable for most engines.
Check the parts catalogue for sizes available.
To fit a piston in a cylinder bore, calculate the size
piston d esired by taking a bore check (fig. 40) and select
the proper size piston to provide the desired clearance.
Chec k t he piston b eing fitted by a ttac hing a tension
scale to th e e nd of a fee le r gauge ribbon (1/2 inch wide)
of t he proper thickness. Position the feeler on the side of
the piston 90 ° from the piston pin hol e. Invert the piston,
then push the piston a nd feeler into the bore parallel to
the crankshaft axis. H old the piston and pull out the
fee ler ribbon, noting the reading on the pull scale
(fig. 45).
If
the scale reading is greater than the maximum
allowable pull, recheck calcul ations to be sure the proper
size piston has been selected, check for a damaged piston,
try a new piston, or hon e the cylinder to obtain the
proper fit.
If the scale readi ng is less than the mmimum allow-
ab le pu ll, recheck calculations before trying another
Fig 45-Fitting Piston-Typical
piston. If none can be fitted, bore the cylinder to the next
size piston. When a piston has been fitted, mark it for
assembly in the cylinder to which it was fitted .
NOTE:
A.ll pistons are tile sOine weight, both standard
and oversize; there/ore, pistons oj various sizes can
be i1ltermixed without upsetting engine balance. Re-
bore only the cylinder or cylinder' which require it.
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6485
Fig . 46-Measurin9 Piston Ring Gap-Typical