IO-390-D Series Engine Maintenance Manual
© 2020 Avco Corporation. All Rights Reserved
72-30
March 2020
Page 225
IO-390-D Series Engine Maintenance Manual
S.
Install the valve rocker shaft cover with a new valve rocker shaft cover gasket, new lock
washers and nuts. Torque the nuts to 96 in.-lb. (11 Nm).
CAUTION
BE SURE THERE IS NO OIL INSIDE THE TAPPET BODIES AND THAT
THE TAPPET PLUNGER AND CYLINDER ASSEMBLY ARE
THOROUGHLY CLEAN AND DRY. WASH ANY LUBRICATING OR
PRESERVATIVE OIL (MINERAL SPIRITS, STODDARD SOLUTION, OR
EQUIVALENT) FROM THESE PARTS, SINCE TAPPET ASSEMBLIES
MUST BE ABSOLUTELY DRY FOR THE TAPPET CLEARANCE CHECK.
NOTICE:
If the clearance between the valve rocker and the cylinder head cannot be brought
within the
Service Table of Limits - SSP-1776
install the standard valve rocker
thrust washer per the latest revision of Service Bulletin No. SB-225 for replacement
valve rocker thrust washers.
T.
Measure the clearance between the valve rocker and cylinder head. Refer to the latest
revision of the
Service Table of Limits - SSP-1776
.
NOTICE:
The procedure to measure dry tappet clearance is the same for intake or exhaust
valves.
U.
To measure the dry tappet clearance:
(1)
Push in on the push rod end of the valve rocker.
(2)
Use a Valve Clearance Gage (ST-23) (Figure 35) to measure the distance between the end
of the valve rocker assembly and the valve stem cap (Figures 36 and 37).
(a)
Insert the 0.028 end of the Valve Clearance Gage (ST-23) between the valve rocker
assembly and the valve stem cap. If it cannot be inserted, use a shorter pushrod.
(b)
Try to insert the 0.080 end of the Valve Clearance Gage (ST-23) between the valve
rocker assembly and the valve stem cap. If it can be inserted, use a longer pushrod.
(3)
The distance must be between 0.028 and 0.080 in. (0.711 to 2.032 mm) (Figure 36).
NOTICE:
If the clearance is not within the prescribed limit, insert a longer or shorter push
rod to obtain the correct clearance. Refer to the latest revision of Service
Instruction No. SI-1060 or the applicable parts catalog for available push rods.
Figure 35
Valve Clearance Gage
(ST-23)
Figure 36
Dry Tappet Clearance
Figure 37
Measuring Dry Tappet
Clearance
V.
Recheck the valve rocker clearance on all cylinders and make any adjustments as required.
