5-17. Fuel System Tubes.
a. Removal Observe the following precautions
when removing tubes.
(1) When loosening a coupling nut, always use
a backup wrench on the mating fitting to prevent the
fitting from turning.
(2) Always use the proper size wrench to pre-
vent rounding off the hex corners.
(3) Attach th e wrench to the fitting or coupling
nut in a manner that will prevent crushing of the fitting
or coupling nut.
(4) Never use a pipe wrench, pliers, or vise
grips on a coupling nut or fitting.
Flush tubes with solvent (item 3, table
2-2) and blow dry.
Inspection. Inspect and reject tubes for the fol-
(1) Rinks or en s which could obstruct fuel
flow. Dents are allowable up to 0.015 in..
(2) Cracked or broken tubes or coupling nuts. If
cracked tubes or coupling nut is suspected, refer to TM
l-1520-254-23, Technical Manual Aviation Unit Main-
tenance (AWM) and Aviation Intermediate Mainte-
nance (AVIM) Manual Nondestructive Inspection
Procedure for OH-58 Helicopter Series.
crushed, or otherwise
damages coupling nuts.
(4) Chafing within clamp areas in excess of
0.010 in. deep. Chafing is not allowed at or near the
flared tubing end.
(5) Nicks which exceed 0.010 in. deep.
(1) Observe the precautions listed in removal
when installing the fuel tubes.
(2) Tighten No. 4 size coupling nuts 80 to 120 in.
lb. and No. 5 size coupling nuts 150 to 200 in. lb.
(3) Rigid steel tubing must align with its mat-
ingfittings in the free state such that both coupling nuts
will engage two full threads of their mating fittings
with light finger pressure. The tube must be stretched
during final tightening of the coupling nuts. Adjust-
ments may be made by bending the tube at the principal
bend or bends. All bending must be accomplished with
the tube removed from the engine. flattening effect as
a result of reforming shall not exceed 15 percent of the
5-17.1. Fuel Check Valve.
(1) Disconnect Fire Shield to Fuel Nozzle Hose
(5, Figure 5-3) from fuel nozzle (6) and fuel check valve
(2) Disconnect fuel control-to-firewall shield
tube (4) from Fuel Check Valve (1).
(3) Remove nut (3) washer (2) and check valve
(1) from the firewall shield.
Visually inspect general condition of valve and
check associated tubing for cracked or broken tubes or
coupling nuts. If cracked tubes or coupling nut is sus-
pected, refer to TM l-1520-254-23, Technical Manual
Aviation Maintenance (AWM) and Aviation Inter-
mediate Maintenance (AVIM) Manual Nondestructive
Inspection Procedure for OH-58 Helicopter Series.
(1) Install the check valve (1) and washer (2) in
the fireshield. Install from the aft side with arrow
pointing rearward. Secure the valve with washer (2)
and nut (3). Tighten 55-80 in. lb.
(2) Install fuel control to check valve tube (4)
and fuel nozzle to check hose (5). Tighten coupling nuts
to 80-120 in. lb.
Section Ill. LUBRICATION SYSTEM
Failure to properly install, align, and
tighten oil fittings and tubes could re-
sult in an engine failure.
Lubrication system servicing includes cleaning and
inspecting the magnetic chip detectors and oil pressure
regulator, changing the system oil, cleaning the oil fil-
ter, removing and reinstalling the oil filter housing, oil
pressure reducer, and lube oil check valves. In addition,
it includes adjusting the oil pressure regulating valve
and the scavenge oil flow check.
6-19. Use of Oils.
It is not advisable to mix MIL-L-7807 and
MIL-L-23699 oils except in cases of emer-
gency. If it becomes necessary, the system
must be flushed within 6 hours of operation.
(Refer to paragraph 5-21.)
Nearly all present day lube oils contain an-
tifoam additives which can settle to the bot-
tom of the container. Thoroughly shake
(agitate) the container prior to adding oil to
the system either at an oil change or during
Use of MIL-L-23699 oil is authorized and di-
rected for ambient temperatures above minus 25°F.
5-16 Change 21