TEXTRON LYCOMING OPERATOR’S MANUAL
O-540 & IO-540 SERIES SECTION 5
NOTE
If
an engine does not have a fill-flowoil filteq change oil ev-
ery 25 hours; also, inspect oil pressure and suction screens
for
metal contamination, and clean thoroughly before reinstalla-
tion.
c. Oil Relief Valve (Non-Adjustable) -The function of the oil pressure
relief valve is not maintain engine oil pressure within specified limits.
The valve, although not adjustable, may be controlled by the addition
of a maximum of nine STD-425 washers under the cap to increase
pressure or the use of a spacer (Textron Lycoming P/N 73629 or
73630) to decrease pressure. A modification on later models has elim-
inated the need for the spacers. Particles of metal or other foreign mat-
ter lodged between the ball and seat will result in faulty readings. It
is advisable, therefore, to disassemble, inspect and clean the valve if
excessive pressure fluctuations are noted.
d. Oil Relief Valve (Adjustable) - The adjustable oil relief valve en-
ables the operator to maintain engine oil pressure within the specified
limits. If the pressure under normal operating conditions should con-
sistently exceed the maximum or minimum specified limits, adjust the
valve as follows:
With the engine warmed up and running at approximately 2000 RPM,
observe the reading on the oil pressure gage. If the pressure is above max-
imum or below minimum specified limits, stop engine and screw the ad-
justing screw out to decrease pressure and in to increase pressure. De-
pending on installation, the adjusting screw may have only a screw drive
slot; or it may have the screw driver slot plus a pinned .37524castellated
nut and may be turned with either a screw drive or a box wrench.
NOTE
Check applicable parts catalog
for
optional sizelpressure-ca-
pacity relief-valvesprings.
4. CYLINDERS. It is recommended that as a field operation, cylinder
maintenance be confined to replacement of the entire assembly. For
valve replacement consult the proper overhaul manual. This should be
undertaken only as an emergency
measure.
Revised January 1999
5-11
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