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IO-390-D Series Engine Maintenance Manual
IO-390-D Series Engine Maintenance Manual
25. Crankshaft Idler Gear Installation
NOTICE: The left crankshaft idler gear has etched circles in two locations. The location with
etched circles on two teeth side-by-side aligns with the single etched circle on the
crankshaft gear (Figure 94). The other location with the etched circle is on a single gear
tooth (Figure 95) and aligns between the two teeth with the etched circles on the
camshaft gear. The correct orientation of these etched circles is necessary to ensure
correct valve timing.
Figure 94
Correct Alignment Between the Crankshaft
Gear and the Left Crankshaft Idler Gear
A. Install the left crankshaft idler gear (Figure 96) in place on the idler shaft with a new bushing
(Figure 2). Turn the crankshaft gear and/or the camshaft gear to align the gears.
B. Install the right crankshaft idler gear with a new bushing on the idler shaft located to the left
of the crankshaft gear.
C. Install a rubber band around the gears to hold them in place (Figure 97).
Crankshaft Idler Gears Installed
26. Crankshaft Endplay Clearance Check
Complete the crankshaft endplay clearance check after the crankshaft is installed and the
crankcase halves have been assembled. Verify the crankshaft endplay clearance is within
acceptable limits.
A. Attach a dial indicator gage to the crankcase starter pad.
B. Move the crankshaft to the rear of the engine as far as possible.
© 2020 Avco Corporation. All Rights Reserved
March 2020
Figure 96
Figure 95
Correct Alignment Between the Camshaft
Gear and the Left Crankshaft Idler Gear
Rubber Band to Hold Crankshaft
Figure 97
Idler Gears
72-20
Page 181
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