Machinery Repairman

Figure 13-4.—Lapping tools.
has the same angle as the valve seat (fig. 13-4). You will
use the lapping tool and grinding compounds in almost
the same way you used the disk in the grinding process.
However, you NEVER use the valve disk as a lap. The
following list shows the essential points you must keep
in mind while using the lapping tool:
Do not bear heavily on the handle of the lap.
Do not bear sideways on the handle of the lap.
Shift the lap-valve seat relation so that the lap
will gradually and slowly rotate around the entire
seat circle.
Check the working surface of the lap; if a groove
wears on it, have the lap refaced.
Use only clean compound.
Replace the compound often.
Spread the compound evenly and lightly.
Do not lap more than is necessary to produce a
smooth and even seat.
Always use a fine grinding compound to finish
the lapping job.
When you complete the lapping job, spot-in and
grind-in the disk to the seat.
Abrasive compound needed to grind-in and lap-in
valve seats and disks is available in Navy stock in four
grades. The following list shows grades and the
recommended sequence of use:
GRADE
Coarse
Figure 13-5.—Valve seat construction.
13-6
USE
To lap-in seats that have deep cuts and
scratches or extensive erosion.
Medium To follow up the coarse grade: also
may be used at the start of the
reconditioning process where damage
is not too severe.
Fine To use when the reconditioning
process nears completion.
Microscopic To finish lap-in and do final grind-in.
fine
REFACING.—The seat of a valve may be so
deeply cut, scored, or corroded that lapping will not
correct the condition. If so, you must machine it, or, in
an extreme case, replace it with a new seat.
Many valves have removable seats that are
threaded, welded, threaded and welded, or pressed into
the valve body. In view A of figure 13-5, the valve
seating surface has been welded so that it has become