Operating instructions

5-1
SECTION V
CLEANING, REPAIR AND REPLACEMENT
5-1. MATERIALS AND PROCESSES.
5-2. Equipment, materials and processes in general
use in aircraft engine overhaul shops are satisfactory
for cleaning IO-520 engine parts.
5-3. Aluminum alloy parts can be degreased by
spraying with any fortified mineral spirit solvent or by
brush application of the same liquid. Fortified mineral
spirits are more effective when the parts are immersed
in them and allowed to remain for a short time to
permit solvent action to loosen caked deposits.
Carbon deposits and gum (oil varnish) may be
removed most easily by immersing these parts in a hot
bath of an inhibited, mild alkaline cleaning compound.
Immersion time should be only as long as necessary to
remove the deposits. Carbon solvent should be
employed only when carbon deposits are too hard and
thick for removal by other solvents. Give special
attention to cleaning studs, tapped holes and drilled
holes. Caution must be exercised in cleaning of all
aluminum alloy engine parts. Do not use any strong
alkaline solutions to clean aluminum alloy castings or
wrought aluminum alloy parts, because strong
solutions will attack and destruct a bare machined
surface. Immediately after removing soaking parts
from a caustic or inhibited, mild alkaline bath, remove
all traces of the alkali by spraying the parts with a jet
of wet steam or by brushing vigorously with a mineral
spirit solvent. Cleaned parts may be dried by use of a
jet of dry compressed air to remove all solvent liquids.
CAUTION
All alkaline residues must be
removed from crevices, recesses and
boles, as well as from other surfaces,
to prevent the formation of a
foaming emulsion in the engine
lubricating oil after reassembly.
5-4. No polishing compound or abrasive paste or
powder should be needed or employed for cleaning
engine parts. Scraping, abrasion with wire brushes,
sandpaper or abrasive cloth and buffing wheels are
dangerous methods to use on soft metals such as
aluminum. Scratches resulting from such methods
allow a concentration of stress at the scratch and may
cause fatigue failure.
5-5. Various blasting techniques can be employed to
remove hard carbon deposits if suitable equipment is
available. The most suitable types of grit for dry
blasting are plastic pellets and processed natural
materials, such as wheat grains and crushed fruit pits
or shells. Air pressure should be the lowest that will
produce the desired cleaning action. Small holes and
finished surfaces which do not require cleaning should
be protected from the blast by seals and covers,
particularly if the grit is sharp. Sand, shot and metal
grit are too abrasive and too heavy for use on soft
metals such as aluminum. After any blasting process,
blow off all dust with dry compressed air and make
sure that no grit has lodged in crevices, recesses and
holes.
5-6. SPECIFIC PARTS.
5-7. CYLINDERS. Precautions applicable to both
aluminum and steel must be exercised in cleaning and
storing these assemblies. Remove oil and loose
material with a mild alkaline cleaner by spraying or
brushing. If stubborn deposits of car- bon remain on
cylinder heads, the areas affected may be vapor
blasted. All machined surfaces must be protected from
abrasive action during the blasting operation.
5-6. PISTONS. Do not use wire brushes or scrapers
of any kind. Soft and moderately hard carbon deposits
may yield to solvent action. If deposits remain, blast
the heads with soft grit or by the vapor grit method,
first having installed tight fitting skirt protectors.
Ring grooves may he cleaned by pulling through them
lengths of binder twine or very narrow strips of crocus
cloth. Do not use automotive ring groove scrapers,