Oil Relief Valve - Lycoming O-320 76 Series Operator's Manual

SECTION 5
MAINTENANCE PROCEDURES
c. Oil Relief Valve (Non-Adjustable) – The function of the oil pressure relief valve is to 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 (Lycoming P/N 73629 or 73630) to decrease pressure. A modification on later models has
eliminated the need for the spacers. Particles of metal or other foreign matter 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 enables the operator to maintain engine
oil pressure within the specified limits. If the pressure under normal operating conditions should
consistently 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 gauge. If the pressure is above maximum or below minimum specified limits, stop engine
and screw the adjusting screw out to decrease pressure and in to increase pressure. Depending on
installation, the adjusting screw may have only a screw driver slot and is turned with a screw driver;
or may have the screw driver slot plus a pinned .375-24 castellated nut and may be turned with either
a screw driver or a box wrench.
4. CYLINDERS. Although the complete procedure for disassembly and reassembly is given here, it is
recommended that, as a field operation, cylinder maintenance be confined to replacement of the entire
assembly. Valve replacement should be undertaken only as an emergency measure.
a. Removal of Cylinder Assembly –
(1) Remove exhaust manifold.
(2) Remove rocker box drain tube, intake pipe, baffle and any clips that might interfere with the
removal of the cylinder.
(3) Disconnect ignition cables and remove spark plugs.
(4) Remove rocker box cover and rotate crankshaft until piston is approximately at top center of the
compression stroke. The approximate position may be located by observing top of piston through
the spark plug hole and also observing that both valves are in the closed position.
(5) Remove the 5/16 x 24 self-locking nut. Thus remove the valve rocker, valve rocker fulcrum shim
and rotator from exhaust valve.
Do not lose shim when valve rocker fulcrum is removed from cylinder head.
(6) Remove push rods by grasping ball end and pulling rod out of shroud tube. Detach shroud tube
spring and lock plate and pull shroud tubes through holes in cylinder head.
The hydraulic tappets, push rods, rocker arms and valves must be assembled in the same
location from which they were removed.
5-6
LYCOMING SERIES OPERATOR'S MANUAL
NOTE
NOTE
O-320