IO-390-D Series Engine Maintenance Manual
72-20
© 2020 Avco Corporation. All Rights Reserved
Page 150
March 2020
IO-390-D Series Engine Maintenance Manual
E.
Measure the diameter of the alignment dowel (Dimension A) shown in Figure 32 and
determine if the measurement conforms to the values for the different alignment dowel part
numbers in the latest revision of Service Bulletin No. SB-475 for additional details.
F.
If the alignment dowel is out of tolerance or out of round, replace the dowel with a new one
per the “Alignment Dowel Replacement” procedure in this chapter.
8.
Crankshaft Bearing Surface Inspection
A.
Examine all bearing surfaces for scoring, galling, and wear.
B.
Refer to the latest revision of
Service Table of Limits - SSP-1776
to identify the nominal
manufactured specifications of the bearing journals. Undersize crankshaft bearing journals in
Table 1 are identified by a code symbol stamped on the front of the flange as a suffix to the
part number.
Table 1
Crankshaft Undersize Codes
Journals
0.003 in. (0.076 mm)
0.006 in. (0.152 mm)
Main Bearing Journals
M03M
M06M
C.
Using a micrometer, measure and record the dimensions.
D.
If the actual undersize is between the service limit (0.0015 in. and 0.003 in.), complete the
following:
(1)
Polish to 0.003 in. (0.076 mm) undersize.
(2)
Fit with 0.003 in. (0.076 mm) bearing insert.
(3)
Repeat for all bearings.
CAUTION
DURING POLISHING, DO NOT ALLOW THE LATHE SPEED TO
EXCEED 150 RPM.
NOTICE:
Polishing undersize is preferable to grinding undersize because shafts that are
polished do not require re-nitriding.
If one bearing journal is polished to 0.003 in. or 0.006 in. undersize, all
corresponding journals must be polished to the same size.
E.
If, after the bearing journal is polished to 0.003 in. (0.076 mm), the bearing journal requires
more polishing complete the following:
(1)
Polish to 0.006 in. (0.152 mm) undersize.
(2)
Fit with 0.006 in. (0.152 mm) bearing insert.
(3)
Repeat for all like bearings.
F.
If the actual undersize is greater than 0.006 in. (0.152 mm), replace the crankshaft.
