Acura NSX 1991 Manual page 114

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Valve Seats
Reconditioning
1. Renew the valve seats in the cylinder head using a
valve seat grinder.
NOTE: If guides are worn (see page 6-39), replace
them (see page 6-40) before grinding the valve seats.
2. Carefully grind a 45° seat, removing only enough
material to ensure a smooth and concentric seat.
3. Bevel the upper edge of the seat with the 30° stone
and the lower edge of the seat with the 60° stone.
Check width of seat and adjust accordingly.
4. Make one more very light pass with the 45° stone
to remove any possible burrs caused by the other
stones.
Valve Seat Width:
Standard (New):
Intake 0.80 - 1.00 mm (0.031 - 0.039 in)
Exhaust 1.25 - 1.55 mm (0.049 - 0.061 in)
Service Limit:
Intake 1.5 mm (0.059 in)
Exhaust 2.0 mm (0.079 in)
SEAT WIDTH
Table of Contents
After resurfacing the seat, inspect for even valve
seating: Apply Prussian Blue compound to the valve
face, and insert valve in original location in the head,
then lift it and snap it closed against the seat sever-
al times.
ACTUAL
SEATING
SURFACE
VALVE
SEAT
PRUSSIAN BLUE COMPOUND
6. The actual valve seating surface, as shown by the
blue compound, should be centered on the seat.
• If it is too high (closer to the valve stem), you
must make a second cut with the 60° stone to
move it down, then one more cut with the 45°
stone to restore seat width.
• If it is too low (closer to the valve edge), you must
make a second cut with the 30° stone to move
it up, then one more cut with the 45° stone to
restore seat width.
NOTE: The final cut should always be made with
the 45° stone.
7. Insert intake and exhaust valves in the head and
measure valve stem installed height.
Valve Stem Installed Height (Intake and Exhaust):
Standard (New): 41.55-42.35 mm
(1.6358-1.6673 in)
Service Limit: 42.435 mm (1.6707 in)
8. If valve stem installed height is over the service limit,
replace the valve and recheck. If still over the service
limit, replace the cylinder head; the valve seat in the
head is too deep.
VALVE STEM
INSTALLED HEIGHT