1.7.4 Idler Gear
DETROIT DIESEL 53
Fig. 3. - Idler Gear Details and Relative Location of Parts
through the end plate and into the counterbore in the
the cylinder block. Then remove the idler gear hub and
the idler gear inner thrust washer as an assembly.
3. Insert two 3/8" - 16 bolts through the idler gear hub
and thread them into the cylinder block, as shown in Fig.
1., to be sure the bolt holes will be in alignment when
Wash the idler gear and bearing assembly, hub and
the flywheel housing is installed.
thrust washers thoroughly in clean fuel oil and dry them
with compressed air. Examine the gear teeth and
4. Insert the 3/8 "-16x1-3/4 " special bolt through the
bearing for scoring, pitting and wear. If the gear teeth
center of the idler gear hub and thread it into the
are worn or the bearing is scored, pitted or worn
cylinder block. Tighten the bolt to 40-45 Ib-ft torque.
excessively, replace the gear and bearing assembly or
Then remove the two 3/8"-16 bolts previously installed
install a new bearing in the gear. Examine the outside
for alignment of the gear hub.
diameter of the idler gear hub and thrust washers; if
scored or worn excessively, replace them.
5. Lubricate the idler gear hub and idler gear bearings
liberally with clean engine oil.
When a new bearing is installed in the idler gear, it must
not protrude beyond the gear face on either side.
6. Position the crankshaft gear and the camshaft gear -
so that their timing marks will align with nose on the idler
Install Idler Gear and Bearing Assembly
gear. Refer to Fig, 1. in Section 1.7.1.
1. Place the inner thrust washer on the forward end of
7. With these timing marks in alignment, install the
the idler gear hub with the flat in the inner diameter of
idler gear as shown in Fig. 2.
the thrust washer over the flat on the end of the gear
hub and with the oil grooves in the thrust washer facing
8. Apply a thin film of cup grease to the inner face
the idler gear.
(face with the oil grooves) of the outer idler gear thrust
washer. Then place the thrust washer over the end of
Place the small protruding end of the idler gear
the idler gear hub with the oil grooves in the side of the
thrust washer facing the idler gear and the flat in the
inner diameter of the thrust washer over the flat on the
end of the idler gear hub.
9. Check the backlash between the mating gears. The
backlash should be .003 " to .005 " between new gears
and should not exceed .007 " between used gears.
1972 General Motors Corp.