Valve seat repair:
A valve seat not producing a uniform contact with its valve or
showing a width of the seating contact that is off the specified
range must be repaired by regrinding or by cutting and regrind-
ing and finished by lapping.
1) EXHAUST VALVE SEAT: Use a valve seat cutter to make
three cuts in the order illustrated in figure. Three cutters must
be used: the first for making the 15
angle, the second for
making the 75
angle and the last for making the 45
seat
angle. The third cut must be made to produce the desired
seat width.
2) INTAKE VALVE SEAT: The cutting sequence is the same as
for exhaust valve seats but the second angle differs, as will
be noted in figure.
3) VALVE LAPPING: Lap the valve on the seat in two steps, first
with a coarsesize lapping compound applied to the face and
the second with a fine-size compound, each time using a
valve lapper according to the usual lapping method.
NOTE:
After lapping, wipe the compound off the valve face
and seat, and produce a contact pattern with a marking
compound (red-lead paste). Check to be sure that the
contact is centered widthwise “a” on the valve seat
and that there is no break in the contact pattern ring.
Be sure to check and, as necessary, adjust the valve
clearance after re-installing the cylinder head and
valve mechanism.
ENGINE MECHANICAL (F8B ENGINE)
6A-23
Seat width for exhaust valve
seat
1.3 – 1.5 mm
(0.0512 – 0.0591 in.)
Seat width for intake valve
seat
1.3 – 1.5 mm
(0.0512 – 0.0591 in.)
