1.7.4
DETROIT DIESEL 53
IDLER GEAR AND BEARING ASSEMBLY
IN-LINE
ENGINES
The engine idler gear and bearing assembly, located at
the flywheel end of the engine, meshes with the
camshaft and crankshaft gears and rotates on a
stationary hub. The hub is secured directly to the
cylinder block by a bolt which passes through the hub
and three bolts which pass through the flywheel
housing, hub and end plate (Fig. I).
On early engines, an idler gear spacer (dummy hub)
was used on the side opposite the idler gear. Currently
Two timing marks (a triangle within a circle) are
the flywheel housing has an integral cast hub and a
stamped on the idler gear diametrically opposite
,015" thick shim is used between the flywheel housing
(180 ) to one another.
and the end plate.
The inside diameter of the idler gear bearing is
2.186 "-2.187 " and the outside diameter of the idler
Remove Idler Gear and Bearing Assembly
gear hub is 2.1825 "-2.1835 ". Therefore, the clearance
(Flywheel Housing Removed )
between the idler gear hub and the idler gear bearing
is 0025" to .0045", with a maximum allowable wear
1. Remove the idler gear outer thrust washer from the
limit of ,007".
idler gear hub (Fig. 3).
A thrust washer is provided on both sides of the idler
2. Slide the idler gear straight back off of the idler
gear and bearing assembly. The standard thickness of
gear hub.
the idler gear and bearing assembly is 1.233" to
1.234" and the standard thickness of the two thrust
3. Remove the bolt which secures the idler gear hub to
washers is ,236" to ,240", thus, the clearance between
the thrust washers and the idler gear is ,006" to
,013", with a maximum allowable wear limit of
,017".
On an In-line engine, the idler gear is positioned on
the left-hand side for a right-hand rotating engine
as viewed from the rear. Refer to Fig. 5 under General
Description.
Fig. 2 Installing Idler Gear
Fig. 1 Installing Idler Gear Hub
SEC. 1.7.4 Page 1
August. 1972
