The pistons are tin-plated aluminum alloy and are
precision machined, cam ground and balanced. Each
piston is fitted with a nickel alloy top ring insert. Three
compression rings and one oil control ring are located
above the piston pin. The top compression ring and the
two scraper segments of the three-piece oil rings are
chrome plated, Holes drilled through the walls of each
piston at the oil ring groove allow excess oil collected in
the groove to return to the oil pan. Pistons are the full
floating type, held in the piston by retainer rings. A
connecting rod and bearing connects each piston to the
14-81 Piston, Rod, and Rod Bearing Removal and Disas-
Syptoms and Isolation Of Malfunction. A mal-
function of a component of the piston assembly is usually
indicated by loss of engine power, increased oil consump-
tion, bluish-white exhaust smoke, excessive engine knock,
or low oil pressure.
b. Removal and Disassembly.
(1) Remove engine assembly. (para. 2-13).
(2) Support engine on block or engine stand.
(3) Remove cylinder head (para. 14-77).
(4) Drain engine oil, and remove the oil pan, oil
pump and discharge tube (para. 14-65).
(5) Remove the piston ring travel ridge from the
cylinder sleeve. (para. 14-85).
(6) Remove the lock bolts securing the connect-
ing rod bearing caps. (See fig. 14-4 1). Remove the bear-
ing caps and free the lower end of the rods from the crank-
shaft. Remove the shells from the bearing.
(7) Carefully remove each piston and rod
assembly by pushing the assembly out through the top of
the cylinder sleeve.
(8) Remove the pin retainer from the groove in
the piston at each end of the piston pin.
(9) Remove the rings from each piston.
Whenever a connecting rod with the piston is
secured in a vise, be extremely careful that the
bottom of the piston skirt is not nicked. Use
lead jaw protectors to protect the bottom of the
skirt from the nicks and to prevent nicks in the
rod which will lead to piston and/or connecting
PISTON AND RINGS
(10) Drive the piston pin from the piston.
Immerse piston in 180°F water for approximately 5
utes. Remove pin while piston is still hot.
The bore in an aluminum alloy piston expands as
the piston heats but provides a tight fit between
pin and piston at room temperature.
14-82 Piston Assembly Inspection and Repair.
a. Clean pistons with cleaning solvent, Federal
Specification P-D-680, and dry them with clean, com-
pressed air. After cleaning, the piston skirt, piston rings,
and ring grooves should be thoroughly inspected. Be sum
oil drain holes in the oil ring grooves are open and clean.
If the cleaning solution does not remove all carbon from
the bottom of the ring grooves, break the old rings in half
and use the butt ends as scrapers. Be careful to remove
only carbon or foreign material; do not scrape away any
metal from the side or bottom of the ring grooves.
b. The piston skirt should be examined for score
marks or other indications of improper piston clearance.
Inspect the inside of pistons for cracks; scored or cracked
pistons should be replaced. Check pistons for wear. The
skirt diameter of a new piston is 4.246-4.247 inches
(measured at right angles to piston pin and bottom of the
skirt); the inside diameter of a new cylinder sleeve is
4.2495-4.251 inches. giving a running clearance of
c. Any deviation from these measurements will
indicate the amount of wear on the piston and/or the cylin-
der sleeve. If the piston assembly and piston rings are
removed from the cylinder sleeve, even after a short
period of operation, do not reinstall the same rings; in
most cases, used rings will not again seat properly. The
outer diameter of new piston rings have tool marks and
reasonably rough surfaces which allow for fast wear-in
and seating of the rings to the cylinder walls. After a
period of operation, the rings wear or lap themselves to fit
perfectly with the cylinder walls and ring seat.
d. If the wear the in piston compression ring
grooves does not create side clearance with new piston
rings greater than 0.011 inch, if piston pin bore does not
exceed 1.5026 inches, and if no cracks or scores are
detected in piston pin bosses, on the skirt or in the com-
bustion chamber rues, the pistons may be reused with a
reasonable life expectancy of one-half to three-fourths that
of new pistons.
e. Inspect the bore of connecting rod with cap in
place and the socket head capscrews tightened to 80 to 85
foot-pounds or the 12 point capscrews tightened to 65 to
65.5 foot-pounds. Using an inside micrometer, measure
dimensions A and B as shown in figure 14-43. Record
dimensions A and B and arrive at an average dimension.
The average dimension must not exceed 2.9705 inches.
Subtract dimensions A and B and the remainder must not
exceed 0.0015 inch, which is the maximum allowable out-
14-88 Change 12