twice the number of teeth as the crankshaft gear so that
Inspect the camshaft end plug in the cylinder
the camshaft rotates at one-half the speed of the
block. Replace if any leaking is evident from the
crankshaft. The camshaft has eight cam lobes, two for
circumference of the plug.
each set of valves. The cam lobes are positioned to
Inspect the camshaft bearings in the cylinder
provide the correct valve opening and closing
block for scoring or visible damage; replace damaged
characteristics for each valve. The camshaft is provided
bearings if necessary. Check the camshaft-to-bearing
with an integral gear which drives the engine oil pump.
clearance, and, if necessary, replace bearings as
The camshaft rides in sleeve bearings which are seated
in the cylinder block.
(1) Temporarily insert the camshaft in the block.
Check the clearance between the camshaft bearing
journals and camshaft bearings with feeler stock cut in
strips ¼s inch wide. Dress the feeler stock with a stone
to eliminate burrs or feathered edges.
With the engine removed from the truck and
between the fan end and drive end bearings and journals
mounted on an engine stand, proceed as follows:
must be between 0.002 and 0.004 inch and the center
Remove the cylinder head (para 9-6).
journal must be between 0.003 and 0.0047.
Remove the valves and valve tappets (para 9-
Remove the gear cover (para 9-19).
Remove the governor parts.
Do not insert the camshaft too far into the block.
Pull the gear (11, fig. 9-6) from the camshaft
If the camshaft bumps the expansion plug on the
drive end of the engine, an oil leak could result.
Remove the two bolts (12) and lockwashers
(13) that secure the thrust plate (14) to the block; remove
(2) If clearance exceeds tolerances, remove the
the thrust plate.
camshaft and remove the camshaft bearings. New
Pull the camshaft (17) from the block.
bearings are pre-reamed. Install new bearings, taking
care to align the oil holes with the passages in the block.
Use caution to prevent damage to the bearings during
Dry cleaning solvent P-D-680 is toxic and
flammable. Wear protective goggles and gloves
and use only in a well ventilated area. Avoid
Lubricate the camshaft bearings with engine
contact with skin, eyes, and clothes and don't
oil and install the camshaft in the block. Position the
breathe vapors. Do not use near open flame or
excessive heat. The flash point is 100°F -
thrust plate (14, fig. 9-6) on the camshaft; secure with
the two bolts (12) and lockwashers (13).
138°F. (38°C - 59°C). If you become dizzy while
Hold the camshaft toward the front of the
using cleaning solvent, get fresh air immediately
engine with a bar inserted into the fuel pump hole. Align
and get medical aid. If contact with eyes is
the timing marks on the camshaft and crankshaft gears
made, wash your eyes with water and get
medical aid immediately.
camshaft. Position the governor drive assembly against
the camshaft gear and secure with nut (10, fig. 9-6).
Cleaning and Inspection
Tighten the nut to 85 to 90 ft/lbs torque.
Clean all parts with cleaning solvent P-D-680
and dry thoroughly.
Inspect the camshaft for cracks, worn or
scored cams, worn or scored bearing surfaces, chipped,
cracked, or broken gear teeth, and clogged oil passages.
Refer to table 9-1 for wear limits. Replace a damaged
Inspect the' thrust washer for scoring and
wear. Replace the thrust washer if any signs of wear are
Inspect the cam gear for cracked, chipped or
broken gear teeth, damaged shaft bore, or worn thrust
surface. The cam gear and the mating gear on the
crankshaft must be replaced as a pair. Do not attempt to
Figure 9-30. Timing Gears Showing Alignment Marks.
replace these gears singly.
Change 1 9-24