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(26) Insert the screwdriver between the Gage (ST-71) and valve spring on the opposite side
and push the valve spring toward the dial indicator as shown in Figure 9.
(27) Relax the screwdriver and record the reading on the dial indicator. For the exhaust valve
guide to be acceptable, the measurement must be within the specified limits in the latest
revision of the Service Table of Limits - SSP-1776.
• If the measurement is greater than the specified limit, either replace the cylinder or
send the cylinder to an authorized vendor who can replace the valve guide.
• If the measurement is less than the specified limit, ream the valve guide per
instructions in the latest revision of Service Instruction No. SI-1425.
(28) Move the piston to near its top end of travel.
(29) Remove the Gage Adapter (ST-71-8) from the valve stem.
(30) Loosen each cap screw in the Gage (ST-71) (Figure 6) in small equal increments to
decrease pressure on the valve spring slowly and equally.
(31) Remove the Gage (ST-71) from the cylinder.
NOTICE: Make sure the plunger assembly is clean and dry. There must be no oil in the
plunger assembly.
(32) Examine and install an acceptable plunger assembly and hydraulic lifter socket (Figure
5) in the exhaust side tappet bore of the crankcase. Refer to the latest revision of Service
Instruction SI-1011 for plunger assembly inspection guidelines.
(33) Apply engine oil mixture (15% pre-lubricant (STP or equivalent) and 85% SAE No. 50
mineral base aviation grade lubricating oil) to the new seal and shroud tube seal (Figure
5).
(34) Install a new seal and the washer into the cup in the exhaust side tappet bore of the
crankcase.
(35) Assemble the new shroud tube seal over the outer end of the shroud tube.
(36) Insert the shroud tube through the hole in the rocker box and seat the end firmly into the
crankcase.
(37) Install the shroud tube spring, new lockplate, and nut. Torque the nut to 96 in.-lb. (11
Nm).
NOTICE: If necessary, turn the nut up to one additional hex to align the flat on the nut with the
tab on the lockplate.
(38) Ensure the flat on the nut aligns with the lockplate tab and bend the tab up. Lockplate
tabs must not be bent up on the corner of the nut.
(39) Make sure that the valves are closed with the piston at TDC of the compression stroke.
(40) Use a brush and apply a mixture of 15% STP or equivalent and 85% SAE No. 50
mineral-based aviation-grade lubricating oil to 1-inch (2.54 cm) of both ends of the push
rods. Refer to the latest revision of Service Instruction No. SI-1059 for any new details.
(41) Install the push rod assembly into the full length of the shroud tube.
(42) Press the push rod tightly from the outer end of the shroud tube to test the spring tension
and free travel of the unloaded or dry hydraulic tappet plungers. Make sure the springs
compress and return.
NOTICE: The valve stem cap (Figure 5) is only on the exhaust valve stem.
72-30
Page 108
YO-233-B2A Engine Maintenance Manual
TEO-540-A1A Engine Maintenance Manual
© 2021 Avco Corporation. All Rights Reserved
February 2021
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