Lycoming YO-233-B2A Maintenance Manual page 126

(12) Examine the exhaust valve key which tends to wear in uniform distinctive patterns.
Replace a worn or damaged valve key. If the key does not need to be replaced, use a
Valve Spring Compressor (ST-25) to compress the exhaust valve springs and install it in
the same position from where it was removed.
(13) Turn the crankshaft to position the piston at the bottom of the compression stroke and
remove the rope from the cylinder.
CAUTION DO NOT MIX PLUNGER ASSEMBLIES WITH DIFFERENT PART
(14) Remove the nut, lockplate, and shroud tube spring (Figure 5). Discard the lockplate.
(15) Remove the exhaust side push rod assembly, shroud tube, hydraulic lifter socket, and
plunger assembly.
(16) Remove the washer and seal from the cup in the exhaust side tappet bore of the
crankcase, and shroud tube seal from the engine cylinder. Discard the seals.
NOTICE: Do not confuse "valve spring seats" with "valve seats," valve spring seats
(Figure 5) are metal disks installed on the ends of the valve springs in the rocker
box and are field replaceable. Valve seats (Figure 15) are installed inside the
cylinder at the surface where the intake or exhaust valve rests during engine
operation when that valve is closed. Valve seats only can be replaced by an
authorized vendor.
(17) Use a cloth dampened with mineral spirits to wipe the oil from the top surface of the
upper exhaust valve spring seat (Figure 5).
(18) Loosen the screws identified in Figure 6 to prevent the screw from touching the Gage
Adapter (ST-71-8) when installed on the valve stem.
(19) Install the Gage (ST-71) on the valve on the cylinder head as shown in Figure 6.
72-30
Page 106
NUMBERS IN THE SAME ENGINE. DIFFERENT PLUNGERS HAVE
VARYING LEAK DOWN RATES WHICH CAN CAUSE INCORRECT
ENGINE OPERATION.
Figure 6
Gage ST-71 Installation on the Cylinder Head
YO-233-B2A Engine Maintenance Manual
TEO-540-A1A Engine Maintenance Manual
© 2021 Avco Corporation. All Rights Reserved
February 2021