Piper Navajo PA-31 Service Manual page 941

PIPER NAVAJO SERVICE MANUAL
4. Remove the two hex nuts (23) and washer (24), and slide the housing inner half (21) off the
motor through bolts. The spacer (7) will drop out.
5. Install new motor brushes as described in Paragraph 13-26, Step b. If the motor commutator
is badly worn, or if the motor is defective in any respect, it must be replaced.
13-42. CLEANING. (Refer to Figure 13-27, 13-28 or 13-29.)
a. Clean individual metal parts (except those parts containing switches and electrical wiring) and the
combustion tube assembly, by immersing them in dry-cleaning solvent, such as Stoddard solvent (Federal
Specification P-D-680). A bristle brush should be used to assist the cleaning process if foreign
accumulations are stubborn to remove.
CAUTION
Do not attempt to buff or scrape off any deposits on face of spray
nozzle. The face of the nozzle is very susceptible to damage from
mishandling. Carefully repeat cleaning process using only a bristle
brush and repeated applications of solvent to loosen any stubborn
deposits.
b. Use compressed air or lintless cloth to dry the parts, unless sufficient time is available for them to
air dry.
c. Wipe electrical components with a clean, dry cloth. If foreign material is difficult to remove,
moisten the cloth in carbon tetrachloride or electrical contact cleaner and clean all exterior surfaces
thoroughly.
13-43. CLEANING AND INSPECTING THE COMBUSTION TUBE ASSEMBLY. (Refer to Figure 13-27,
13-28 or 13-29.)
a.
Slight scaling and discoloration of the combustion tube assembly is a normal condition for units
that have been in service up to 1000 airplane hours. The slight scaling condition will appear to be mottled
and a small accumulation of blue-gray powder may be present on the surface in certain areas. This
condition does not require replacement of combustion tube assembly, unless severe overheating has
produced soft spots in the metal.
NOTE
This assembly should be inspected prior to cleaning in order to
prevent the removal of visible evidences of damage.
b.
Look inside the exhaust outlet to determine if the combustion tube appears to be heavily scaled
or mottled. Deformation is more difficult to detect visually but can usually be observed by looking straight
through the combustion tube assembly and sighting along the outer surface of the inner combustion tube.
An assembly that has been obviously deformed should be replaced. Slight deformation will not affect
heater operation unless it is extensive and localized enough to reduce the flow of ventilating air through the
heater more than 10 percent.
c. The combustion tube assembly may be cleaned by either of two methods:
1.
One method is to soak the combustion tube assembly overnight in an Oakite M-S Stripper
solution, made by mixing one pound of Oakite salts with each gallon of water used. The solution should be
maintained at a temperature of between 190°F and 210°F. After overnight soaking, rinse the combustion
tube assembly thoroughly in water to remove all traces of the Oakite solution. In order to reach all areas of
the combustion tube assembly, it is advisable to let it stand in the rinsing water for as long as 1/2 hour,
while occasionally agitating it to circulate the water. All openings should be left open during this operation.
Be sure to dry the combustion tube assembly thoroughly after cleaning.
Reissued: 10/12/79
HEATING AND VENTILATING SYSTEM
5C11