ALLIS-CHALMERS
VALVES AND SEATS
142A. Intake and exhaust valves are
not interchangeable and the intake
valves on all models seat directly in
cylinder head with a face and seat
angle of 45 degrees. The exhaust
valves seat on renewable ring type
inserts with a face and seat angle of
45 degrees. The method of removing
the renewable type valve seat inserts
is shown in Fig. AC55. Valve seat
width is ^-inch for both the intake
and the exhaust. Seats can be nar-
rowed, using 15 and 75 degree stones.
Intake and exhaust valves have a stem
diameter of 0.3095-0.3100.
Adjust the intake valve tappet gap
to 0.010 hot and the exhaust valve
tappet gap to 0.019 hot.
VALVE GUIDES AND SPRINGS
142B.
Guides can be pressed or
driven from cylinder head if renewal
is required. Press guides into cylinder
head with smaller O.D. of guide up,
until top of the guide is ^^-inch above
the valve cover gasket surface of
cylinder head. Maximum allowable
valve stem to guide clearance is 0.006.
Ream new guides after installation,
to provide the recommended stem to
guide clearance of 0.0015-0.003. Refer
to paragraph 142A for valve stem
diameter.
142C.
Intake and exhaust valve
springs are interchangeable in all
models. Renew any spring which is
rusted, discolored or does not meet
the load test specifications which
follow:
Spring free length
2)^2
inches
Renew if less than Iff inches
Pounds pressure
at
1 %
inches 40- 50
Pounds pressure
at 1^ inches 105-115
VALVE TAPPETS
(CAM FOLLOWERS)
142D.
The 0.560-0.561 diameter
mushroom type tappets operate di-
rectly in the unbushed cylinder block
bores with a suggested clearance of
0.0005-0.0025. Maximum allowable
clearance is 0.0035.
To remove the tappets, it is first
necessary to remove the camshaft as
outlined in paragraph 144. Tappets
are available in standard size only.
ROCKER ARMS
143.
The hollow rocker arm shaft
is drilled for lubrication to each rock-
er arm bushing. Lubricating oil to
the drilled cylinder head passage and
slotted oil stud (S—Fig. AC55A)
is supplied by an external oil line
which is connected to the main oil
gallery on left side of engine. CAU-
TION: Always check the slotted stud
to be sure the slot is facing the oil
passage in the head. If oil does not
flow from the hole in the top of each
rocker arm, check for foreign mate-
rial in the external oil line or in the
cylinder head passage.
Fig.
AC55A—Rocker arms assembly Is lu-
bricated via the slotted stud (SK
ParagrapKs 142A-143B
The procedure for disassembling and
reassembling the rocker arms from
the shaft is evident. Check the rock-
er arm shaft and the bushing in each
rocker arm for excessive wear. Maxi-
mum allowable clearance between the
shaft and bushings is 0.005. When in-
stalling new bushings, make certain
that oil hole in bushing is in register
with oil hole in rocker arm and ream
the bushings to provide a clearance
of 0.001-0.002 for the 0.8405-0.841 di-
ameter rocker arm shaft. When in-
stalling the rocker arm shaft, make
certain that the oil metering holes in
the shaft point toward push rods in-
stead of valve stems.
Inspect the valve stem contact but-
ton in the end of each rocker arm for
being mutilated or excessively loose. If
either condition is found, renew the
contact button. Extract the button
retaining snap ring as shown in Fig.
AC55B and remove the button and oil
wick. Install new oil wick and button
and test the button for a free fit in
the rocker arm socket.
Note: If a new contact button has
any binding tendency in the rocker
arm socket, use a fine lapping com-
pound and hand lap the mating sur-
faces.
VALVE TIMING
143A. Valves are properly timed
when timing marks on camshaft gear
and crankshaft gear are in register.
The single punch marked tooth space
on the camshaft gear should be
meshed with the single punch marked
tooth on the crankshaft gear, as shown
at (X) in Fig. AC56.
CRANKCASE FRONT COVER
143B.
To remove the crankcase front
cover (timing gear cover), first drain
the cooling system and remove the
Fig.
AC55B—Rocker arms
are fitted with renewable
type valve stem contact
buttons which can be re-
moved after extracting the
retaining snap rings as
shown.
Fig.
AC55—Method of removing a valve
sear insert.
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