1991 ACURA NSX Service Repair Manual

7. If camshaft-to-holder oil clearance is out of

tolerance:

Rotate camshaft

while measuring

8. Check cam lobe height wear.

Cam Lobe Height Standard (New):

M/T

A/T

EXHAUST
INTAKE
CYLINDER

NUMBER
REAR BANK
INTAKE
FRONT BANK

CYLINDER

NUMBER

EXHAUST
Check this area for wear.

Cam position

P: Primary M: Mid S: Secondary
And camshaft has already been replaced, you

must replace the cylinder head.

If camshaft has not been replaced, first check to-

tal runout with the camshaft supported on V-

blocks.

Camshaft Total Runout:

Standard (New): 0.03 mm (0.0012 in)

Service Limit: 0.06 mm (0.0024 in)

If tne total runout of the camshaft is within toler-

ance, replace the cylinder head.

If the total runout is out of tolerance, replace the

camshaft and recheck. If the bearing clearance

is still out of tolerance, replace the cylinder head.ProCarManuals.com

VALVE SPRING COMPRESSOR
Snap-on CF711
Valves, Valve Springs and Valve Seals

Replacement

NOTE: Identify valves and valve springs as they are re-
moved so that each item can be reinstalled in its original

position.

1. Using an appropriate-sized socket and plastic mallet, lightly tap the valve retainer to loosen the valve keep-
ers before installing the valve spring compressor.
PLASTIC MALLET

SOCKET

2. Install spring compressor. Compress spring and re- move valve keeper.

VALVE SPRING COMPRESSOR
ATTACHMENTEXTENSION

07MAF–PR9010A
VALVE SPRING
COMPRESSOR
ATTACHMENT

07757–PJ1010A
3. Install the special tool as shown.
VALVE SEAL

COMMERCIALLY AVAILABLE
VALVE GUIDE SEAL REMOVER

LISLE P/N 57900 OR KD 3350

SEAL

PULLER

4. Remove the valve guide seal.ProCarManuals.com

Intake Valve Dimensions
A Standard (New): 34.9 — 35.1 mm
(1.374-1.382 in)

B
Standard (New):
111.05-111.40
mm
(4.372-4.386 in)

C Standard (New): 5.475—5.485 mm
(0.2156-0.2159 in)

C Service Limit: 5.445 mm (0.2144 in)
D Standard (New): 1.05—1.35 mm
(0.041-0.053 in)

D Service Limit: 0.85 mm (0.033 in)
Exhaust Valve Dimensions
A Standard (New): 29.9—30.1 mm

(1.177-1.185 in)

B Standard (New): 109.60-109.90 mm
(4.315-4.327 in)

C Standard (New): 5.45-5.46 mm
(0.2146-0.2150 in)

C Service Limit: 5.42 mm (0.2134 in)
D Standard (New): 1.65—1.95 mm
(0.065-0.077 in)

D Service Limit: 1.45 mm (0.057 in)
Cylinder Head Height;
Standard (New): 150.95-151.05
(5.943-5.947 in)

Service Limit: 150.8 mm (5.937 in) Measure along edges, and 3 ways across center.
NOTE: If camshaft-to-holder oil clearances (page 6-38)
are not within specification, the head cannot be

resurfaced.

If camshaft-to-holder oil clearances are within
specifications, check the head for warpage.
Cylinder Heads

Warpage

If warpage is less than 0.05 mm (0.002 in) cylinder
head resurfacing is not required.If warpage is between 0.05 mm (0.002 in) and 0.2
mm (0.008 in), resurface cylinder head.
Maximum resurface limit is 0.2 mm (0.008 in) based
on a height of 151 mm (5.945 in).
PRECISION STRAIGHT EDGEProCarManuals.com

Intake Valve Dimensions
A Standard (New): 34.9 — 35.1 mm
(1.374-1.382 in)

B
Standard (New):
111.05-111.40
mm
(4.372-4.386 in)

C Standard (New): 5.475—5.485 mm
(0.2156-0.2159 in)

C Service Limit: 5.445 mm (0.2144 in)
D Standard (New): 1.05—1.35 mm
(0.041-0.053 in)

D Service Limit: 0.85 mm (0.033 in)
Exhaust Valve Dimensions
A Standard (New): 29.9—30.1 mm

(1.177-1.185 in)

B Standard (New): 109.60-109.90 mm
(4.315-4.327 in)

C Standard (New): 5.45-5.46 mm
(0.2146-0.2150 in)

C Service Limit: 5.42 mm (0.2134 in)
D Standard (New): 1.65—1.95 mm
(0.065-0.077 in)

D Service Limit: 1.45 mm (0.057 in)
Cylinder Head Height;
Standard (New): 150.95-151.05
(5.943-5.947 in)

Service Limit: 150.8 mm (5.937 in) Measure along edges, and 3 ways across center.
NOTE: If camshaft-to-holder oil clearances (page 6-38)
are not within specification, the head cannot be

resurfaced.

If camshaft-to-holder oil clearances are within
specifications, check the head for warpage.
Cylinder Heads

Warpage

If warpage is less than 0.05 mm (0.002 in) cylinder
head resurfacing is not required.If warpage is between 0.05 mm (0.002 in) and 0.2
mm (0.008 in), resurface cylinder head.
Maximum resurface limit is 0.2 mm (0.008 in) based
on a height of 151 mm (5.945 in).
PRECISION STRAIGHT EDGEProCarManuals.com

SEAT WIDTH
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 otherstones.

Valve Seat Width:
Standard:
IN
0.80-1.00
mm
(0.031-0.039
in)

EX 1.25-1.55 mm (0.049-0.061 in.)

Service Limit: IN 1.5 mm (0.059 in)
EX 2.0 mm (0.079 in)

1. Renew the valve seats in the cylinder head using a
valve seat grinder.
NOTE: If guides are worn (page 6-43), replace them(page 6-44) before grinding the valve seats.
Valve Seats
Reconditioning
5. After resurfacing the seat, inspect for even valveseating: 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
7. Insert intake and exhaust valves in the head and measure valve stem installed height.
Valve Stem Installed Height (IN and EX): Standard (New): 41.55-42.35 mm

(1.6358-1.6673 in)

Service Limit: 42.435 mm (1.6707 in)

VALVE STEM
INSTALLED HEIGHT

8. If
valve stem
installed
height
is
over
the
service
limit,
replace valve and recheck. If still over the service
limit, replace cylinder head; the valve seat in the head

is too deep.

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.ProCarManuals.com

Valve Guides

Valve Movement

Measure the guide-to-stem clearance with a dial indica-

tor while rocking the stem in the direction of normal thrust

(wobble method).

Intake Vaive Stem-to-Guide Clearance:

Standard (New): 0.05—0.11 mm

(0.002-0.004
in)

Service Limit: 0.16 mm (0.006 in)

Exhaust Valve Stem-to-Guide Clearance:

Standard (New): 0.10—0.16 mm

(0.004-0.006
in)

Service Limit: 0.22 mm (0.009 in)

Valve extended 10 mm out from seat.

If measurement exceeds the service limit, recheck

using a new valve.

If measurement is now within the service limit,

reassemble using a new valve.

If measurement still exceeds limit, recheck using

alternate method below, then replace valve and

guide, if necessary.
NOTE: An alternate method of checking guide to

stem clearance is to subtract the O.D. of the valve

stem, measured with a micrometer, from the I.D. of

the valve guide, measured with an inside

micrometer or ball gauge.

Take the measurements in three places along the

valve stem and three places inside the valve guide.

The difference between the largest guide measure-

ment and the smallest stem measurement should

not exceed the service limit.

Intake Valve Stem-to-Guide Clearance:

Standard (New): 0.025 — 0.055 mm

(0.001-0.002 in)

Service Limit: 0.08 mm (0.003 in)

Exhaust Valve Stem-to-Guide Clearance:

Standard (New): 0.05—0.08 mm

(0.002-0.003
in)

Service Limit: 0.11 mm (0.004 in)ProCarManuals.com

4. Working from the camshaft side, use the driver and
an air hammer to drive the guide about 2 mm

towards the combustion chamber. This will knock

off some of the carbon and make removal easier.

VALVE GUIDE DRIVER
07742–0010100
5. Turn the head over and drive the guide out toward the camshaft side of head.

If a valve guide still won't move, drill it out with a
5/16 inch bit, then try again.

CAUTION: Drill guides only in extreme cases: you
could damage the cylinder head if the guide breaks.
6. Remove the new guide(s) from the refrigerator, one
at a time, as you need them.

Do not use a torch; it may warp the head.
Do not get the head hotter than 300 °F (150°C)
excessive heat may loosen the valve seats.
To avoid burns, use heavy gloves when handling
the heated cylinder head.
Valve Guides

Replacement

1. As illustrated in the removal steps of this pro- cedure, use a commercially—available air-impact
driver attachment modified to fit the diameter of
the valve guides. In most cases, the same pro- cedure can be done using the Valve Guide Driver

and a conventional hammer.

COMMERCIALLY AVAILABLE
VALVE GUIDE DRIVER
5.3 mm

(0.21
in)

87 mm
(3.43 in.)
57 mm

(2.24 in.)
10.8
mm

(0.42
in)

Removal and Installation

VALVE GUIDE DRIVER
07742–0010100

2. Select the proper replacement guides and chill them in the freezer section of a refrigerator for about an

hour.

3. Use a hot plate or oven to evenly heat the cylinder
head to 300°F (150°C). Monitor the temperature

with a cooking thermometer.

CAUTION: Always wear safety goggles or a face shield when
using the air hammer.
Hold the air hammer directly in line with the valve
guide to prevent damaging the driver.
CAUTION:ProCarManuals.com

7. Slip a 6 mm steel washer and the correct driver at-
tachment over the end of the driver (The washer willabsorb some of the impact and extend the life of the
driver).

DRIVER 6 mm WASHER ATTACHMENT

8. Install the new guide(s) from the camshaft side of
the head; drive each one in until the attachment bot-
toms on the head. If you have all twelve guides todo, you may have to reheat the head one or twomore times.

VALVE GUIDEDRIVER, 5.5 mm

07742-0010100
Valve Guide Installed Height:
Intake: 13.75-14.25 mm (0.541-0.561 in)

Exhaust: 13.75-14.25 mm (0.541-0.561 in) Valve Guide Reaming
NOTE: For new valve guides only.
1. Coat both reamer and valve guide with cutting oil.
2. Rotate the reamer clockwise the full length of the valve guide bore.
3. Continue to rotate the reamer clockwise while removing it from the bore.
4. Thoroughly wash the guide in detergent and water to remove any cutting residue.
5. Check clearance with a valve (page 6-43).

REAMER HANDLE VALVE GUIDE
REAMER, 5.5 mm

07HAH-PJ7010A

Turn reamer in

clockwise direction

only.

Verify that the valve slides in the IN, EX valve
guides without exerting pressure.ProCarManuals.com