2. Measure the vertical runout of the valve
stem by rolling the stem on a piece of plate glass
and measuring any gap with a feeler gauge. The
runout should not exceed the service limit in
3. Measure valve stems for wear (Figure
Replace the valve if the stem diameter is less
than the wear limit in Table 1.
4. Remove all carbon and varnish from the
valve guides with a stiff spiral wire brush.
5 . Inspect the valve/guide clearance; insert
each valve in its guide. Hold the valve just
slightly off its seat and rock it sideways, then at
a right angle to the first check (Figure 45). If it
rocks more than the limit in Table 1, the guide
is probably worn and should be replaced.
Take the cylinder head to a dealer and have
the valve guides measured and replaced if
necessary. Installation of new guides requires
special installation and reaming tools.
7. Inspect the valve seats. If worn or burned.
they must be reconditioned with special cutting
or grinding tools. This work should be done by
your dealer or local machine shop. If you are
performing the work yourself, see Table 1 at the
end of this chapter for valve seat specifications
8. Seats and valves in near-perfect condition
can be reconditioned by lapping with fine
carborundum paste. Lapping, however, is
always inferior to precision grinding or cutting.
Valve lapping is a simple operation which
can restore the valve seal without machining if
the amount of wear or distortion is not too
Valve lapping is not a substitute .for
precision grinding or cuttirzg of valves
and their seats. Get a professional
opinion on whether or not lapping will
do the job before you settle for it.
1. Coat the valve seating area in the head with
a lapping compound such as Carborundum or
2. Insert the valve into the combustion
3. Wet the suction cup of a lapping stick
(Figure 47) and stick it onto the head of the
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