IO-390-D Series Engine Maintenance Manual
72-30
© 2020 Avco Corporation. All Rights Reserved
Page 196
March 2020
IO-390-D Series Engine Maintenance Manual
Table 2
Summary of Cylinder Compression Check Results and Corrective Action
Results
Indication
Corrective Action
Differential pressure of
70 psi (483
kPa) or more
for an engine cylinder
Satisfactory
No corrective action necessary.
Differential pressure of
61 to 69 psi
(
421 to 441 kPa
) for an engine
cylinder
Wear has
occurred
Complete the Cylinder Compression Check
again after the next 100-hour engine
operating interval - record results.
Monitor the differential pressure.
Differential pressure of
60 psi (414
kPa)
or less for an engine cylinder
Cylinder worn
or not in
conformance
Either manually turn the crankshaft three
times or start the engine and operate for 3
minutes and repeat the Cylinder Compression
Check.
If the results of the second Cylinder
Compression Check are too low, listen for
airflow at the exhaust and intake ports.
Identify all of the causes and complete the
necessary corrective action.
Difference of
5 psi (34 kPa)
or less)
between engine cylinders (Pressure
readings for all engine cylinders
must be nearly equal.)
Satisfactory
No corrective action necessary.
Difference of
6 to 15 psi (41 to 103
kPa)
between engine cylinders.
Repeat the Cylinder Compression Check
after the next 10 hours of engine operation. A
valve can reseat itself and show satisfactory
compression again. If the difference remains
between
6 to 15 psi (41 to 103 kPa)
after the
second Cylinder Compression Check,
identify all of the causes and complete the
necessary corrective action.
Difference of
15 psi (103 kPa)
or
more between engine cylinders
Start and operate the engine for 3 minutes
and repeat the Cylinder Compression Check.
If the difference between engine cylinders is
still
15 psi (103 kPa)
or more, replace all of
the engine cylinders.
Air escaping at spark plug spot face
Fluorescent
Penetrant
Inspection of
area shows
cracks
Replace the cylinder with a cylinder kit.
Leak check at the spark plug port
seals (using a soap solution) shows
bubbling around spark plug port
seal.
Heli-Coil
®
insert requires
replacement.
Complete the “Heli-Coil
®
Replacement”
procedure in this chapter.
