Lycoming IO-390-D Series Maintenance Manual page 222

Summary of Cylinder Compression Check Results and Corrective Action
Results
Differential pressure of 70 psi (483
kPa) or more for an engine cylinder
Differential pressure of 61 to 69 psi
(421 to 441 kPa) for an engine
cylinder
Differential pressure of 60 psi (414
kPa) or less for an engine cylinder
Difference of 5 psi (34 kPa) or less)
between engine cylinders (Pressure
readings for all engine cylinders
must be nearly equal.)
Difference of 6 to 15 psi (41 to 103
kPa) between engine cylinders.
Difference of 15 psi (103 kPa) or
more between engine cylinders
Air escaping at spark plug spot face
Leak check at the spark plug port
seals (using a soap solution) shows
bubbling around spark plug port
seal.
72-30
Page 196
IO-390-D Series Engine Maintenance Manual
IO-390-D Series Engine Maintenance Manual
Table 2
Indication
Satisfactory No corrective action necessary.
Wear has Complete the Cylinder Compression Check
occurred again after the next 100-hour engine
operating interval - record results.
Monitor the differential pressure.
Cylinder worn Either manually turn the crankshaft three
or not in times or start the engine and operate for 3
conformance 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.
Satisfactory No corrective action necessary.
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.
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.
Fluorescent Replace the cylinder with a cylinder kit.
Penetrant
Inspection of
area shows
cracks
Complete the "Heli-Coil
®
Heli-Coil
insert requires procedure in this chapter.
replacement.
© 2020 Avco Corporation. All Rights Reserved
Corrective Action
Replacement"
®
March 2020