It is unnecessary to remove discolor-ation and light scoring from piston skirts. Abrasive cloth
must not be used on the piston skirts because the diameters and cam-ground contour must not
be altered. Heavily scored or burned pistons should
be
discarded. And it is recommended that
pistons be replaced during major engine overhaul regardless of condition.
Honing of cylinder walls for any reason is justification for complete piston ring replacement.
72-20-04 VALVES.
After degreasing valves, inspect them and discard any whose head is warped excess-
ively, or insufficient stock to permit
refacing within specified limits, or whose stem is
burned, scored, eroded or nicked. Carbon deposits may be loosened by solvent action or they
may be scraped off while the valve is rotated in a polishing head or lathe collet. Apply
crocus cloth moistened in mineral spirit, and polish the stems with dry crocus cloth. Replace-
ment of exhaust valves is recommended at major overhaul regardless of condition.
I
Intake valve refacing figure 72-20-28C.
72-20-05 ROCKER SHAFTS.
100%
replacement at overhaul.
Degrease these parts by brushing on
mineral spirit solvent. Prior to magnetic inspection, polish the steel bearing surfaces with
crocus cloth moistened with kerosene, then with dry crocus cloth.
72-20-06 PUSHRODS, VALVE ROCKERS AND SMALL STEEL PARTS.
Degrease these parts with mineral
spirit solvent. Giving special attention to removal of sludge from all oil passages. Blow
compressed air thru
pushrod.
72-20-07 CAMSHAFT AND CRANKSHAFT.
All parts must be degreased by brushing or spraying with
mineral spirit solvent. Give particular attention to threads, oil holes and recesses. Before
magnetic inspection, the crankpins, main journals, oil seal race of the crankshaft and all
journals, cam lobes and gear mount flange of the camshaft must be smoothed with crocus
cloth,
moistened in mineral spirits. This is to be accomplished while shaft is rotated
in a
high speed lathe (about 100
RPM).
All gum (varnish) deposits must be removed to permit
reliable magnetic indications.
72-20-08 CRANKCASE.
The oil passages must be pressure-flushed with mineral spirit solvent and
I
inspected with the aid of a flashlight. If the castings are immersed in an alkaline bath,
follow this by spraying with steam followed by flushing the oil passages with solvent. After
the castings dry, inspect them thoroughly for alkaline residues, and
remove any traces of
scum.
72-20-09 GEARS.
Gears without bushings are freed of hard deposits by immersion in a caustic stripping
bath, when cold solvents are not effective. Bushings are discolored by this treatment, there-
fore, bushed gears must be cleaned by other methods. Spray or brush with a mineral spirit
solvent using a brass wire brush.
WARNING
.
. .
Do not pressure blast gears, blasting
will
remove hardened surface.
72-20-10 SHEET METAL PARTS AND INTAKE MANIFOLD.
Clean these parts by spraying or brushing
with mineral spirit solvent, or use a cold emulsion type cleaner and flush with water to
rinse.
Immediately after cleaning bare steel
parts, spray or dip them in clean engine oil or, for
longer storage, in a corrosion-preventive oil mixture. Wrap ball bearings in waxed paper.
Wrap or cover other clean parts to protect them from abrasive dust in the air.
72-20-04
DECEMBER
1992
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