IO-390-D Series Engine Maintenance Manual
© 2020 Avco Corporation. All Rights Reserved
72-20
March 2020
Page 147
IO-390-D Series Engine Maintenance Manual
Crankshaft Inspection Checklist for IO-390-D Series Engines (Cont.)
Item
Comments
Findings/
Corrective Action
Done
Counterweight Inspection (Cont.)
Examine the surface of the
counterweight for scoring,
scratches, punch marks, or
any other surface damage.
Make sure the
counterweight surface is
smooth.
Replace the counterweight
if there is scoring, scratches,
punch marks, or any other
surface damage or if the
counterweight surface is not
smooth.
If one or more cracks are
found on the counterweight,
replace the counterweight*.
Outcome of Counterweight
Position 1 inspection:
Accept
Replace
Outcome of Counterweight
Position 2 inspection:
Accept
Replace
Findings / Comments:
Complete Non-Destructive
Test (NDT) (magnetic
particle inspection) on the
counterweights.
Refer to Chapter 05-50.
Findings / Comments:
Examine the bushing bore
on the counterweight for
roundness and for any
scratches, etching, galling
or any other surface
damage. Measure the
bushing bore diameter on
the counterweight.
Replace the counterweight
if the bushing bore on the
counterweight is not round,
not smooth, is out of
tolerance, or has surface
damage.*
Outcome of Bushing Bore
Inspection for Counterweight
Position 1
Accept Replace
Outcome of Bushing Bore
Inspection for Counterweight
Position 2
Accept Replace
(a)
If the counterweight has a letter B marking, the bushing
bore diameter must be between 0.9384 and 0.9392 in.
(23.8354 and 23.8557 mm).
(b)
If the counterweight does NOT have a letter B marking,
the bushing bore on the counterweight is smaller and
must be between 0.9369 and 0.9377 in. (23.7973 and
23.8176 mm).
Bushing Bore Diameter
Counterweight Position 1:
Bushing Bore Diameter
Counterweight Position 2:
NOTICE:
If the bushing bore on the counterweight is not within the specified tolerances, replace
the counterweight. Some counterweights must be replaced as a matched set.*
CAUTION
DO NOT INCREASE THE DIAMETER OF THE BUSHING BORE ON A
COUNTERWEIGHT. THIS ENLARGEMENT CAN CAUSE ENGINE
DAMAGE BECAUSE IT WILL DECREASE THE SNAP RING GROOVE
DEPTH IN THE BUSHING BORE ON THE COUNTERWEIGHT.
*Refer to the latest revision of Service Instruction Nos. SI-1012 and SI-1535 for part numbers and
instructions to replace counterweights and rollers.
