IO-390-D Series Engine Maintenance Manual
© 2020 Avco Corporation. All Rights Reserved
72-30
March 2020
Page 229
IO-390-D Series Engine Maintenance Manual
19.
Barrel Glaze and Varnish Removal from Interior Cylinder Barrel
A.
Use a self-centering, self-bottoming hone that follows a choke located in the top of the
cylinder barrel.
B.
Use kerosene or light engine oil for lubrication while honing.
C.
Put the deglazing hone in a low-speed drill.
D.
Surface hone each cylinder barrel with a minimum of six to eight passes over the glazed
surface, using a smooth up and down motion of the hone to achieve a good cross-hatch
pattern on the cylinder barrel wall.
E.
Thoroughly clean the hone.
F.
Wipe as much of the abrasive build-up from the cylinder walls and recesses as possible,
especially the recesses formed by the top of the cylinder barrel and the bottom of the cylinder
head.
G.
Make a hooked tool from soft wire and rub the tool back and forth in the recess to loosen any
built-up abrasive. Complete this task each time the cylinder is flushed. There must not be any
abrasive material in this area.
H.
Complete the “Cylinder Cleaning” procedure in Chapter 05-30.
I.
Lubricate the internal cylinder barrel thoroughly with SAE 50 engine oil or a rust
preventative oil that conforms with MIL-C-6529.
NOTICE:
If step wear is found inside the cylinder barrel, measure it using the dial bore gage
usually used to measure cylinder diameter. If the depth of the step wear is less than
0.0025 in. (0.0635 mm), remove the step as per the previous steps to remove
cylinder barrel glaze. If the barrel contains a wear step exceeding 0.0025 in. (0.0635
mm), replace the cylinder.
In some cylinders, a small rough area can be found at either end of the barrel
extending less than 0.250 in. (6.35 mm) from the end. This condition is a result of
the manufacturing process and has no effect on the quality or condition of the barrel.
20.
Heli-Coil
®
Replacement
NOTICE:
The IO-390-D Series engines have long reach spark plugs.
A.
Replace the spark plug Heli-Coil
®
insert (Figure 40) in the cylinder head if the threads in the
spark plug hole in the cylinder are damaged (usually occurs when hard carbon on the end of
the spark plug causes the insert to unwind during spark plug removal).
Figure 40
Heli-Coil
®
