TM 9-3431-254-14&P
in a different position to insure a uniform seat which
assembly, shown in Fig. B-50, from the cylinder head.
will show entirely around the valves. After valves
Take out shaft setscrew from bottom of bracket with
have been lapped in evenly, remove and wash both
a 1/8" Allen wrench, and tap shaft out toward set
valves and head thoroughly with kerosene and re-
screw end of bracket, using a brass rod.
assemble.
In reassembly be sure set screw seat in shaft is lined
Valve guides in the cylinder head are replaceable.
up with tapped hole in bracket. After tightening set
The valve stem has a clearance of .002" to .004" in
screw in place, prick punch threads to prevent screw
the guide. When the clearance becomes .006", the
from falling out. Lubricate shaft so that rocker arm
guide should be driven out and a new guide pressed
bearings won't operate `dry' when engine is started.
in place. Allow 1/32" to 1/64" clearance between
the valve guide boss and the bottom of the valve
guide shoulder. Check guide for .3440 /.3445" I.D.
Pull tappets outward to clear lobes while camshaft is
after pressing in place. Ream if necessary.
being removed. Withdraw tappets from inside the
VALVE SEAT INSERTS are not replaceable, due to
crankcase. In reassembly, clean and lubricate tappets.
method of installing. If seat inserts become worn and
Insert thrust plunger and spring into end of camshaft,
ground down to the extent that the seats are wider
as these hold shaft in place endwise. See Fig. B-52.
than the valve face, replace cylinder head.
The camshaft gear has offset mounting holes to pro-
vide accurate assembly for valve timing. The gear can
ROCKER ARM ASSEMBLY (Fig. B-50)
only be out on the correct way for matching up the tim-
Very little wear will occur to the rocker arms as long
ing mark with that of the crankshaft. See Fig. B-52.
as they are adequately lubricated. If replacement is
necessary, remove the complete rocker arm bracket
Note: Beginning with engine serial No. 4904657, a
shell type center main bearing replaces the split rol-
ler bearing. The bearing and hanger assemblies are
not interchangeable for service replacement unless
the complete crankshaft assembly is changed and the
The following instructions apply to the current pro-
duction engines with shell center main bearing. Refer
to Page B-33 for overhaul procedures relative to the
now obsolete roller type center main bearing and crank-
shaft oil collet.
Caution: Do not attempt to remove crankshaft from en-
gine without first removing center bearing hanger.
With reference to Fig. B-53, disconnect oil pressure line
at center bearing hanger and at oil header behind fil-
ter, by using a 1/2 inch hex tubing nut wrench, Re-
move hanger to case screws and washers. Then loosen
and back out cap to hanger screws about 1/2 inch.
Tap screw heads lightly and alternately with a ham-
mer to break cap away from hanger body.
B-31