GMC 1976 ZEO 6083 Maintenance Manual page 688

any cooling fins . A conventional type valve spring
lifter may be used when removing the valve spring
locks, which are of the split type . Clean all carbon
deposits from the cylinder heads, piston tops, valves,
guides, etc. If a valve face is burned or warped, or the
stem worn, install a new valve.
Valve locks are split, tapered typed, the smaller
diameter of which must face toward the valve head .
Tappets are also replaceable from the valve chamber,
after first removing the valve assemblies .
The valve
face
angle is 44°. The valve
seat
angle
is 45° as shown in Figure 6. This 1 ° interference angle
results in a sharp seating surface between the valve
and the top of the valve seat. The interference angle
method of grinding valves minimizes face deposits
and lengthens valve life .
CAUTION: The valves should not be hand
lapped, because the sharp contact may be
destroyed. This is especially important
where stellite faced valves and seats are
used.
Valve faces should be finished to 44°. Valve seats
should be ground with a 45° stone and the width of
the seat band should be 1/32" to 3/64" wide . Grind
only enough to assure proper seating.
Remove all grinding compound from engine
~J T
ic
^4SO
J
tic
FR F ti
RIGHT
c F
VALVE
WRONG
SEAT
A-1595
Figure 6-Valve Interference Angle
ONAN MOTOR GENERATOR
24C- 1 1
parts and place each valve in its proper location .
Make pencil marks at intervals across the valve face
and observe if the marks rub off uniformly when the
valve is rotated part of a turn against the seat.
TAPPET ADJUSTMENT (FIGURE 7)
The engine is equipped with adjustable valve tap-
pets . The valve tappet clearance should be checked
and adjusted, when necessary. Adjust the valve clear
ance only when engine is at ambient temperature.
Proceed as follows :
1 . Remove all parts necessary to gain access to
valve tappets.
2. Remove spark plugs to ease the task of turning
the engine over by hand .
3. Use the engine flywheel to turn the engine over
slowly by hand until the left hand intake valve opens
and closes . Continue turning the flywheel until the
TC mark is on the top and lined up with the TC mark
on the gear cover . Both valves should be closed . This
should place the left hand piston at the top of its
compression stroke, the position it must be in to get
proper valve adjustment for the left cylinder .
4. For the intake valve, a .003" thickness gauge
should just pass between valve stem and tappet .
5. For the exhaust valve, a .010" thickness gauge
(.012" on the 6KW) should just pass between valve
stem and tappet .
6. To correct the valve clearance, use a 7/16"
open end wrench to turn the adjusting screw to ob-
Figure 7-Adjusting Valves