IO-390-D Series Engine Maintenance Manual
© 2020 Avco Corporation. All Rights Reserved
05-30
March 2020
Page 37
IO-390-D Series Engine Maintenance Manual
B.
Dry the crankshaft counterbore threads with compressed air.
Figure 1
Threads in the Crankshaft Counterbore
C.
Clean the threads of the crankshaft counterbore (Figure 1) as follows:
(1)
Use the correct sized undamaged bottoming tap for a 5/16-24 thread size.
CAUTION
TO PREVENT MAKING THE THREADS IN THE CRANKSHAFT
COUNTERBORE TOO LARGE, USE THE CORRECTLY SIZED TAP.
IF THE INCORRECT TAP IS USED, THE BORE CAN BE MADE TOO
LARGE TO CORRECTLY ENGAGE THE THREADS ON THE
CRANSKHAFT GEAR BOLT WHEN THE CRANKSHAFT GEAR IS
INSTALLED ON THE CRANKSHAFT. IF THE BOLT THREADS ARE
TOO LARGE, DISCARD THE CRANKSHAFT AND REPLACE IT
WITH A NEW CRANKSHAFT.
(2)
Install the tap into the recessed counterbore on the crankshaft.
(3)
Turn the tap as necessary to clean the threads.
(4)
Remove the tap.
(5)
Flush the crankshaft counterbore and alignment dowel pin with mineral spirits (MIL-
PRF-680) or equivalent or Stoddard Solvent, or equivalent solvent to remove any debris.
(6)
Dry the crankshaft counterbore threads with compressed air.
(7)
Examine the threads in the crankshaft counterbore for any wear.
(8)
Make sure the tapped hole is clean and the threads are not stripped, galled, or damaged. If
the threads are stripped, galled, or damaged, discard the crankshaft and replace it with a
new crankshaft.
4.
Crankshaft Gear Cleaning
A.
Soak the crankshaft gear in mineral spirits (MIL-PRF-680) or equivalent or Stoddard
Solvent, or equivalent solvent.
B.
Remove all dirt and debris from the crankshaft gear with a lint-free wipe.
C.
Dry with compressed air.
D.
Complete the “Crankshaft Counterbore Cleaning” procedure in this chapter.
