IO-390-D Series Engine Maintenance Manual
© 2020 Avco Corporation. All Rights Reserved
12-30
March 2020
Page 93
IO-390-D Series Engine Maintenance Manual
Table 1 (Cont.)
Fault Isolation Guide
Problem
Cause
Corrective Action
Ref.
Low oil pressure
(Cont.)
Failed or failing
bearings
NOTICE:
Metal in the
oil filter element or oil
suction screen is a sign
of excessive bearing
wear.
Drain the oil from the oil sump.
Open the crankcase and examine the
bearings. Refer to “Tappet, Main
Bearing, and O-Ring Removal”
or
It is recommended the engine be sent
to Lycoming Engines for evaluation.
Include a description of the problem.
12-10
72-05
72-20
Oil pump not operating
correctly
Remove and examine the oil pump.
72-25
Oil pressure gage not
operating correctly
Test the oil pressure gage.
AMM
Excessive oil
consumption
New piston rings are not
completely seated
(break-in not done).
As part of break-in, operate the engine
at not less than 65% power for the first
50 hours.
IOM
Piston rings are worn,
broken, or incorrectly
installed
OR
Cylinder barrels are
glazed or worn too
much
1.
Complete the “Cylinder
Compression Check Procedure.”
2.
Complete the “Cylinder Borescope
Inspection Procedure” to determine
if further corrective action is
necessary
NOTICE:
Listen for a hissing sound
at the breather of the crankcase which
is an indication of air leaks around the
rings.
72-30
3.
Remove the cylinders, hone the
cylinder barrels, replace the piston
rings, and re-install the cylinders as
per the following sections:
•
Cylinder Removal
•
Piston Removal
•
Piston Inspection
•
Piston Ring Replacement
•
Barrel Glaze and Varnish
Removal from Interior Cylinder
Barrel
•
Piston Installation
•
Cylinder Installation
72-30
