Lycoming IO-390-D Series Maintenance Manual page 240

NOTICE: Lycoming manufactures pistons with a taper that extends from the top to the bottom of the
skirt with the smaller diameter at the top.
Section Through Piston Showing Points for Measuring Diameter
Inspection Item
Measure the inside diameter of the
piston pin hole (Figure 20).
Measure the piston diameter at the
top ring land of the piston between
the top and second compression
ring grooves (at a right angle to the
piston pin hole) (Figure 20).
Measure the diameter
approximately 1/8 in. above the
bottom of the piston skirt. (at a
right angle to the piston pin hole)
(Figure 20).
Measure the piston ring clearance.
**Compare the actual measurement against the limits in the latest revision of the Service Table of
Limits - SSP-1776. Replace the piston if any of the measurements are out of tolerance.
72-30
Page 214
Piston Inspection Checklist (Cont.)
Figure 20
Cylinder 1 Cylinder 2 Cylinder 3 Cylinder 4
Actual
Measurement**
SSP-1776
Actual
Measurement**
SSP-1776
Actual
Measurement**
SSP-1776
Actual
Measurement**
SSP-1776
IO-390-D Series Engine Maintenance Manual
IO-390-D Series Engine Maintenance Manual
Findings/Corrective Action
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March 2020