ACURA NSX 1991 Service Repair Manual

RUBBER BAND
WASHERS EXHAUST ROCKER
Replace. SHAFT INTAKE ROCKER

SHAFT

Rear Cylinder Head:

SEALING BOLTS 20 mm60N .
m (6.0 kg-m, 43 Ib-ft) INTAKE ROCKER
SHAFT
WASHERS
Replace. EXHAUST ROCKER
SHAFT
Front Cylinder Head:
SEALING BOLTS 20 mm
60N .
m (6.0 kg-m, 43 Ib-ft)
RUBBER BAND
EXHAUST ROCKER ARM ASSEMBLIES

Rocker Arms and Shafts

Locations

Identify parts as they are removed to ensure reinstallation in original locations.
Inspect rocker shafts and rocker arms (pages 6-36 and 37).
Rocker arms must be installed in the same position if reused.
Install the rocker arms after torquing the cylinder head bolts. Prior to reinstalling, clean all the parts in solvent, dry them and apply lubricant to any contact surfaces.
RUBBER BAND
CYLINDER NUMBER
CYLINDER NUMBER
RUBBER BAND

NOTE:

CAUTION: After installing the rocker shaft orifice, try to turn the rocker shaft to make sure that the orifice has been

inserted in the hole of the rocker shaft correctly. If the orifice is in place, it should not turn.

EXHAUST ROCKER ARM ASSEMBLIESINTAKE ROCKER ARM ASSEMBLIESProCarManuals.com

Rocker Arms and Lost Motion Assemblies

Inspection

NOTE: When reassembling the primary rocker arm, care-

fully apply air pressure to the oil passage of the rocker

arm.

PRIMARY ROCKER ARM

MID ROCKER ARM

SECONDARY

ROCKER ARM

PISTONS

1. Inspect the rocker arm pistons. Push them

manually.

PRIMARY

MID

SECONDARY

Apply oil to the pistons when reassembling.

Bundle the rocker arms with rubber bands to

keep them together as sets.
LOST MOTION ASSEMBLY
2. Remove the lost motion assembly from the cylinder

head and inspect it. Pushing it gently with the finger

will cause it to sink slightly. Increasing the force on

it will cause it to sink deeper.

Push

NOTE:
Check piston movement
If they do not move smoothly, replace the rocker

arm assembly.
If the lost motion assembly does not move

smoothly, replace it.ProCarManuals.com

Rocker Arms and Shafts
Clearance
Measure both the intake rocker shafts and exhaust rocker
shafts.

1. Measure diameter of shaft at first rocker location.

MICROMETER

Surface should be smooth.

2. Zero gauge to shaft diameter.

MICROMETER

CYLINDER BORE
GAUGE
Inspect rocker arm

face for wear.

Repeat for all rockers.
3. Measure inside diameter of rocker arm and check for

out-of-round condition.

Rocker Arm-to-Shaft Clearance (IN and EX):
Standard (New):
Primary and Secondary:
0.025-0.052 mm (0.0010-0.0020 in)

Mid:
0.024-0.053 mm (0.0009-0.0021 in)

Service Limit: 0.08 mm (0.003 in)

If over limit, replace rocker shaft and all over-

tolerance rocker arms.
NOTE: If any rocker arm needs replacement, replace
all three rocker arms in that set (primary, mid, and secondary).ProCarManuals.com

Camshafts

Inspection

1. Put the camshafts, the camshaft holders and holder pipes on the cylinder head, and then tighten

the bolts to the specified torque.

NOTE: Apply clean engine oil to 8 mm bolt threads.
Specified torque: 8 mm x 1.25 mm bolts:
22N .
m (2.2 kg-m, 16 Ib-ft)
6 mm x 1.0 mm bolts: 10N .
m (1.0 kg-m, 7 Ib-ft)

CAMSHAFT HOLDER BOLTS TORQUE
SEQNUENCE

FRONT:

REAR:
PLASTIGAGE STRIP
2. Seat the camshaft by pushing it toward left end of
cylinder head.
3. Zero the dial indicator against the left end, then push the camshaft back and forth, and read the end play.Camshaft End Play:
Standard (New): 0.05—0.15 mm

(0.002-0.006
in)

Service Limit: 0.5 mm (0.02 in)
4. Remove the bolts, then remove the camshaft holders from the cylinder head.
Do not rotate the camshaft during inspection.
Remove the rocker arms and rocker shafts.

NOTE:

Lift camshaft out of cylinder head, wipe clean,
then inspect lift ramps. Replace camshaft if lobes
are pitted, scored, or excessively worn. Clean the camshaft bearing surfaces in the
cylinder head, then set camshaft back in place.
Insert plastigage strip across each journal.

5. Install the camshaft holders, and then tighten the

bolts to the specified torque, as shown in the left
column on this page.
6. Remove the camshaft holders and measure widest portion of plastigage on each journal.
Camshaft-to-Holder Oil Clearance:
Standard (New):
0.050-0.089
mm

(0.002-0.004 in)

Service Limit: 0.15 mm (0.006 in)ProCarManuals.com

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