When a great deal of grinding is necessary on a badly
burned or worn seat, a condition such as that shown in
figure 3-53 will occur. When this happens, you should
narrow and center the valve seat by using a 20 degree
stone to cut down the upper portion of the valve seat,
and a 70 degree stone to cut down the lower portion of
the seat. Figure 3-54 illustrates a valve seat that has
been narrowed down from the top of the valve seat.
Grinding with the narrowing stones usually requires
only a few seconds. Check often while grinding so that
you will not remove too much metal.
CHECKING ROCKER ARMS.--After rocker
arms have been removed, they should be inspected for
wear or damage. Rocker arms with bushings can be
Figure 3-54.--Correct valve seat after narrowing seat.
rebushed if the old bushing is worn. On some rocker
arms, the valve ends, if worn, can be ground down on
engine speeds. They also ensure proper valve seating
the valve refacing machine. Excessively worn rocker
and provide a safety factor in case one spring should
arms should be discarded.
The silent lash rocker arm can be disassembled by
Test valve springs for uniformity and strength. For
removing the eccentric retaining pin. If more than one
an accurate test, use a valve spring tester (fig. 3-55)
rocker arm is being disassembled, do not mix the parts;
when one is available. If a valve spring tester is not
make sure all parts go back into the rocker arms from
available, place used springs on a level surface beside a
which they were taken. When reassembling a rocker
pair of new springs. Use any straightedge to determine
arm, make sure the eccentric is installed so that the
irregularities in height. Replace worn out springs with
recessed dot (which is on the side with the smaller
new ones. Unequal or cocked valve springs will offset,
radius) is next to the plunger.
in the assembled job, all the precision that has been put
into the grinding operation.
When reinstalling rocker arms and shafts in the
cylinder head, make sure that the oil holes (in shafts so
When you have reassembled an engine after
equipped) are on the underside so they will feed oil to
reconditioning the valves, make sure the adjusting
the rocker arms. Be sure that all springs and rocker arms
screws are backed off before rotating the engine. A
are restored to their original positions as the shafts are
valve that is too tight could strike and damage the piston
attached to the head.
or the valve, or both.
CHECKING VALVE SPRINGS.--While work-
ing with valves, you may notice that some of them have
more than one spring. These additional springs are
coiled to offset a tendency of the valve to vibrate at high
Figure 3-55.--Valve spring tester.
Figure 3-53.--Valve seat too wide and low in block.