IO-390-D Series Engine Maintenance Manual
72-30
© 2020 Avco Corporation. All Rights Reserved
Page 216
March 2020
IO-390-D Series Engine Maintenance Manual
Piston Inspection Checklist (Cont.)
Comments:
If inspection of the piston shows the original ground surface of the piston skirt to be undamaged, the
piston is acceptable and can be re-installed.
If any of the following conditions are found on the piston, replace the piston.
•
Damage
•
Cracked, bent, or broken lands, scored skirts or any out-of-tolerance dimensional limits
•
Piston grooves worn to the extent that relatively high steps or ridges are on the lower lands
NOTICE:
Refer to the applicable parts catalog to identify a replacement piston and associated rings.
B.
Piston Ring End-Gap Check
CAUTION
DURING THE PISTON RING END-GAP CHECK, USE CARE NOT TO
SCRATCH OR SCORE THE PISTON OR CYLINDER BORE.
(1)
Lubricate the piston ring, piston, and cylinder bore with a light coating of a mixture of
15% pre-lubricant (STP or equivalent) and 85% SAE 50 mineral-base aviation-grade
lubricating oil
(2)
Put one of the piston rings in the cylinder in which it will be used.
(3)
To square the piston ring in the cylinder bore, install the piston in the cylinder and use a
soft mallet to tap the dome end of the piston on the inside, until the bottom of the piston
skirt is flush with the end of the cylinder barrel. Remove the piston from the cylinder.
(4)
Measure the piston ring end-gap with feeler gauges. Record the measurement in the
Piston Inspection Checklist. Compare the measurement with the ring end-gap
measurement in the latest revision of the
Service Table of Limits - SSP-1776
.
(5)
If necessary to increase the end-gap, carefully file the ends of the piston ring.
(6)
Repeat this check for each piston ring to be used in each cylinder.
