Yamaha XZ550RJ 1982 Service Manual page 55

CAUTION:
If the valve seat is obviously pitted or worn, it
should be cleaned with a valve seat cutter. Use
the 45° cutter. When twisting the cutter, keep an
even downward pressure to prevent chatter
marks.
If cutting section A of the valve seat, use a
30° cutter. If cutting section B, use the 45°
cutter. If cutting section C, use the 60° cut-
ter.
2. Measure the valve seat width. Apply me-
chanic's bluing dye (such as Dykem) to the
valve face and valve seat, apply a very
small amount of fine grinding compound
around the surface of the valve face, insert
the valve into position, and spin the valve
quickly back and forth. Lift the valve, clean
off all grinding compound, and check the
valve seat width. The valve seat and valve
face will have removed the bluing wherever
they contacted each other. Measure the
seat width with vernier calipers. It should
measure approximately 1.0mm (0.039 in).
The valve-seat contact area should be one
uniform width. If the valve seat width varies
or if pits still exist, further cutting will be
necessary. Remove just enough material to
achieve a satisfactory seat.
3. If the valve seat is uniform around the pe-
rimeter of the valve face but is too wide or
not centered on the valve face, it must be
altered. Use either the 30°, 45°, or 60° cut-
ters to correct the improper seat location in
the manner described below:
•
If the valve face shows that the valve seat is
centered on the valve face but is too wide, then
lightly use both the 30° and the 60° cutters to
reduce the seat width to 1.0mm (0.039 in).
•
If the seat shows to be in the middle of the
valve face but to narrow, use the 45° cutter un-
til the width equals 1.0mm (0.039 in).
•
If the seat is too narrow and right up near the
valve margin, then first use the 30° cutter and
then the 45° cutter to get the correct seat width.
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