ACURA NSX 1991 Service Repair Manual

Special Tools
Ref.
No.
Tool Number Description

Qty
Page Reference
Valve Guide Reamer, 5.5 mm
Test Harness
Tappet Adjuster
Tappet Locknut Wrench
Valve Spring Compressor

Attachment Extension

Test Harness
VTEC PlugA/T Low Pressure Gauge
A/T Low Pressure Gauge W/Panel
A/T Pressure Hose, 1700 mm
Valve Guide Driver, 5.5 mm
Valve Spring Compressor Attachment
1
1
1
1
1
1
1

1

1

1
6-45
6-13
6-55

6-55

6-40
6-13
6-52,
53

6-18,
19

6-44,
45

6-40ProCarManuals.com

Cylinder Head/Valve Train
Illustrated Index

CAUTION: To avoid damaging the cylinder head, wait

until the engine coolant temperature drops below
100 °F (38 °C) before removing it.NOTE:

CAP NUT

6 x 1.0 mm
10 N .
m
(1.0 kg-m,

7 Ib-ft)
CYLINDER

HEAD COVER

WASHER AND

GROMMET

After installation, fill the engine with oil up to the

specified level, run the engine for more than 3

minutes, then check for oil leakage.

When installing the new crankshaft;

tighten the crankshaft pulley bolt to 280 N .
m (28

kg-m, 203 Ib-ft),

loosen bolt.


retighten it to

250 N .
m (25 kg-m, 181 Ib-ft).

CYLINDER HEAD

COVER
RUBBER SEALS
Replace when damaged

or deteriorated.

6 x 1.0 mm
12N .
m (1.2 kg-m,

9 Ib-ft)

TIMING BELT
REAR MIDDLE

COVER

TIMING BELT
FRONT MIDDLE

COVER
ADJUSTING BOLT

10 x
1.25
mm

43N .
m (4.3 kg-m,

31 Ib-ft)

For adjustment only,
do not remove.

ALTERNATOR

BELT

Adjustment,
section 23

6 x 1.0 mm
12N .
m
(12
kg-m.

9 Ib-ft)

CRANKSHAFT PULLEY
Remove any oil.

SPECIAL BOLT
16x 1.5 mm

250N .
m (25 kg-m,

181 Ib-ft

Tightening torque for
a new crankshaft.

203

Apply oil to
the bolt threads, but not
to the surface that contacts the washer.
6 x 1.0 mm

12N .
m (1.2 kg-m,

9 Ib-ft)
AIR CONDITIONING (A/C) BELT
Adjustment, section 22
6x 1.0 mm

12N .
m (1.2 kg-m, 9 Ib-ft)

(cont'd)

A/C ADJUSTING

PULLEY BRACKET

RUBBER SEAL
Install with concave

surface facing out.

Remove any oil.
TIMING BELT

DRIVE PULLEY

Remove any oil.

Install with concave
surface facing in.
Remove any oil.

TIMING BELT

Inspection, page 6-22
Adjustment, page 6-22 Replacement, page 6-23 to 26
RUBBER SEALS

Replace when damaged
or deteriorated.
CAP NUT

6 x 1.0 mm

10N .
m (1.0 kg-m,

7 Ib-ft)

TIMING BELT

LOWER COVER

RUBBER SEAL
KEY

Remove any oil.

TENSIONER

280

250N.m

25
kg-m,
181 Ib-ft)

(28
0
0
0

Use new O-rings and gaskets when reassembling.

Replace rubber seals, if damaged or deteriorated.

Prior to installing the cylinder head cover, apply a thin

layer of liquid gasket to the mating surface of the

cylinder head cover and rubber seals to prevent the
rubber seal from falling off.ProCarManuals.com

Cylinder Head/Valve Train

Use new 0-rings and gaskets when reassembling.
Replace rubber seals, if damaged or deteriorated.

Illustrated Index (cont'd)

6 x 1.0 mm
10N .
m (1.0 kg-m.
7 Ib-ft)

8x
1.25
mm

22N.
m (2.2 kg-m. 16 Ib-ft)

Apply oil to the bolt threads.

FRONT INTAKE
CAMSHAFT

RUBBER SEALS

FRONT EXHAUST
CAMSHAFT
OIL SEAL Replace.
DOWEL PIN
CAMSHAFT PULLEY
CRANKSHAFT POSITION (CKP)/ CYLINDER POSITION (CYP) SENSOR
6x1.0
mm
12N ·
m (1.2 kg-m,
9 Ib-ft)
RUBBER SEALS Replace when damaged

or deteriorated.

TIMING BELT
COVER PLATE
6x1.0
mm

12N ·
m (1.2 kg-m.
9 Ib-ft)
10 x
1.25
mm

70N .
m (7.0 kg-m.

51 Ib-ft) DOWEL PIN

CAMSHAFT HOLDER

DOWEL PIN
O RING
Replace.

NOTE:ProCarManuals.com

REAR VARIABLE VALVE TIMING
AND VALVE LIFT ELECTRONIC CONTROL
SYSTEM (VTEC) SOLENOID VALVE

Troubleshooting, page 6-15, 16
EXHAUST GAS
RECIRCULATION (EGR) VALVE

6x1
.0mm 12N .
m (1.2kg-m,
9 Ib-ft)
FILTER Replace.
8x 1.25mm

22N .
m (2.2 kg-m,

16 Ib-ft)
ENGINE COOLANT
TEMPERATURE (ECT) SENSOR 180 N .
m (1.8 kg-m. 13 Ib-ft)

8x 1.25mm
22N .
m (2.2 kg-m, 16 Ib-ft)

FRONT VTEC SOLENOID VALVE

'Troubleshooting, page 6-15, 16

O-RING
Replace.
GASKET

Replace.
ROCKER

SHAFTS WASHERS

Replace.
SEALING BOLTS

60N.m (6.0 kg-m,

43 Ib-ft)
OIL PRESSURE GAUGE SENDING
UNIT (section 23)

8x 1.25mm
22N .
m (2.2 kg-m,

16 Ib-ft)

DOWEL PIN

O-RING
Replace.
ECT SWITCH

28 N ·
m
(2.8 kg-m.
20 Ib-ft)

O-RING

Replace.

ROCKER ARM ASSEMBLY
(PRIMARY, MID, SECONDARY)

Inspection, page 6-36

ROCKER SHAFT

ORIFICE

Remove with 5 mm

bolt and clean.

O-RING

Replace.

(cont'd)ProCarManuals.com

Cylinder Head/Valve Train

Illustrated Index (cont'd)

To avoid damaging the cylinder head, wait until the engine coolant temperature drops below 100°F (38°C) before

removing it.
In handling a metal gasket, care should be taken not to fold it or damage the contact surface of the gasket.

Prior to reassembling, clean all the parts in solvent, dry them, and apply lubricant to any contact parts.

INTAKE VALVE
SPRING OUTER
CYLINDER HEAD BOLTS
11x1.5mm

78N .
m (7.8 kg-m, 56 Ib-ft

Apply engine oil to

the bolt threads.
INTAKE VALVE
SPRING INNER
VALVE SEAL
VALVE GUIDE

LOST MOTION

ASSEMBLY
VALVE KEEPERS
SPRING RETAINER
VALVE SPRING SEAT CYLINDER HEAD BOLTS

11 x
1.5m
78N .
m (7.8 kg-m, 56 Ib-ft)
Apply engine oil to

the bolt threads.

VALVE SPRING SEAT EXHAUST VALVE
SPRING
SPRING RETAINER

VALVE KEEPERS

VALVE SEAL
VALVE GUIDE
LOST MOTION

ASSEMBLY

Test, 6-36

CYLINDER HEAD
GASKET (METAL) Replace.
DOWEL PINS
CYLINDER HEAD ORIFICE

Remove with 6mm

bolt and clean.

O-RINGS

Replace.

OIL CONTROL JET

Remove with 6mm

bolt and clean.

DOWEL PIN
CYLINDER HEAD
GASKET (METAL)
Replace. EXHAUST VALVE
INTAKE VALVE

CAUTION:

NOTE: Use new O-rings and gaskets when reassembling.ProCarManuals.com

1. Disconnect the 2P connector from the VTEC
solenoid valve.
2. Measure resistance between the YEL (front) or BLU/YEL (rear) terminal and body ground.
Resistance: approx 14—30 ohms 4. If filters are normal, push the VTEC solenoid valve
with your finger and check its movement.

FILTER

Replace.
YEL (front) or BLU/YEL (rear)
3. If the resistance is within specifications, remove the VTEC valve assembly from the cylinder head,and check the VTEC valve filter for clogging.
VTEC VALVE
ASSEMBLY
VTEC VALVE
FILTER

Replace.

6 x 1.0 mm
12 N ·
m (1,2 kg-m, 9 Ib-ft)

If there is clogging, replace the engine oil filter

and engine oil.
6x1.0
mm

12 N .
m (1.2 kg-m, 9 Ib-ft)

If VTEC solenoid valve is normal, check the
engine oil pressure.
VTEC Valve Inspection

VTEC

14
30ProCarManuals.com

Remove any oil.
TIMING BELT

Inspection, page 6-22

Adjustment, page 6-22

6 x 1.0 mm
12N .
m(1.2kg-m,9 Ib-ft)
Timing Belt
Illustrated Index
Turn the crankshaft so that the No. 1 piston is at top
dead center (TDC) (page 6-25, 26)
Replace rubber seals if damaged or deteriorated.
Prior to installing the cylinder head cover, apply a thin
layer of liquid gasket to the mating surface of the cylinder head cover and rubber seals to prevent the
rubber seal from falling of.
CYLINDER HEAD COVER
CAP NUT

6x 1.0 mm

10N .
m (1.0 kg-m, 7 Ib-ft)
CAP NUT

6 x 1.0 mm

10N .
m (1.0 kg-m,
7 Ib-ft)

WASHER

RUBBER SEALS
Replace when damaged

or deteriorated.

ADJUSTING BOLT
10 x
1.25
mm

43N .
m (4.3 kg-m,31 Ib-ft)

For adjustment only,

do not remove.
Remove any oil.

COLLARS

RUBBER SEALS

Replace when damaged
or deteriorated.

6 x 1.0 mm
12N .
m (1.2 kg-m.
9 Ib-ft)
6x1.0
mm
12N .
m (1.2 kg-m.
9 Ib-ft)

TIMING BELT
FRONT MIDDLE

COVER

CRANKSHAFT
PULLEY

Remove any oil.
6 x 1.0 mm

12N .
m (1.2 kg-m.

9 Ib-ft)

SPECIAL BOLT
16 x 1.5 mm

250N .
m (2.5 kg-m,

181 Ib-ft)

Tightening torque for
a new crankshaft.

Apply oil to the bolt threads,
but not to the surface

that contacts the washer.

280


0

250N.m

28

0

25
kg-m.

203

0

181 Ib-ft LOWER COVER

RUBBER SEAL
After installation, fill the engine with oil up to the

specified level, run the engine for more than 3
minutes, then check for oil leakage.
When installing a new crankshaft; i tighten the crankshaft pulley bolt to 280N.m (28
kg-m, 203 Ib-ft), loosen it, retighten it to 250
N.m (25 kg-m, 181 Ib-ft).ProCarManuals.com

Rotate pulley and

Inspect belt.
for wear.

1 . Remove the ignition coil covers and harness clamps.
2. Disconnect the connectors, then remove the ignition
coils.
3. Remove the cylinder head covers.
4. Inspect the timing belt for cracks and coolant or oil

soaking.

NOTE:

TDC MARK
BLUE MARK

ADJUSTING BOLT

43N
.
m (4.3 kg-m.

31 Ib-ft)

Direction

of rotation

POINTER ON

LOWER COVER
Tension Adjustment

Always adjust timing belt tension with the engine cold.

Do not rotate the crankshaft when adjusting bolt is

loose (the timing belt will skid over the teeth of the
rear intake camshaft pulley).

Never adjust the belt tension on any other occasion

than when the belt is removed.

shaft pulley.
3. Loosen the timing belt adjusting bolt 180° (the slack
Then, tighten the timing belt adjusting bolt.

4. Verify the No. 1 piston at TDC (page 6-26).

5. Rotate the crankshaft clockwise 9-teeth on cam- shaft pulley (The blue mark on crankshaft pulley
should line up with the pointer on lower cover).
6. Loosen the timing belt adjusting bolt.
7. Retighten the adjusting bolt, torque to 43 N .
m (4.3
kg-m, 31 Ib-ft).

at


should be eliminated).

quence of


and

by turning each cam-
Replace the belt if coolant or oil soaked.
Remove any oil or solvent that gets on the belt.

Inspect this area

Timing Belt
Inspection
CAUTION:

NOTE:
Tensioner is spring-loaded to apply proper tension to
the belt automatically after making the following ad-
justment.
Inspect the timing belt before adjusting the belt
tension.
Always rotate the crankshaft clockwise. Rotating it
counterclockwise may result in improper adjustment
of the belt tension or cause the belt to jump a tooth on the camshaft pulleys.
1 . Install the timing belt with the No. 1 piston at TDC
(page 6-25, 26).

2. Fix the crankshaft, remove the slack in the se-ProCarManuals.com

13. Remove the breather hose, and the air cleaner case
(page 5-22).

(cont'd)

WATER HOSES

Do not disconnect.

EXPANSION TANK
12. Remove the expansion tank.
NOTE: Do not disconnect water hoses.

6x 1.0 mm
10N .
m (1.0kg-m, 7 Ib-ft)
IGNITION COIL

CONNECTOR

6 x 1.0 mm

12N .
m (1.2kg-m,
9 Ib-ft)
6x1.0
mm

12 N .
m
(1.2 kg-m.

IGNITION COIL
CAUTION: Inspect the water pump when replacing the
timing belt (page 10-11).

O-RING
Replace.

8*
1.25
mm
8x
1.25
mm

22N.
m (2.2 kg-m,

16 Ib-ft)
5. Lower the car.
6. Remove the strut bar (page 5-19).
7. Remove the intake manifold plate. 8. Remove the top cover (page 5-21).
9. Remove the ignition coil covers.
10. Remove the injector cover and the wire harness
covers.
11. Remove the ignition coils and the connecters.
22N
.
m (2.2 kg-m,

16 Ib-ft)

Replace.

Removal

9 Ib-ft)
HARNESS
COVERS
COVER

6x 1.0 mm

10N .
m (1.0 kg-m,
7 Ib-ft)

FR

There are front and rear ignition coils and covers.
They can be identified by the mark FF (front) or RR (rear) printed on them.
When installing front and rear ignition coil covers, attach a rubber seal to the intake side.

NOTE:

Before removing the timing belt, mark direction of ro-
tation if it is to be reused.

NOTE:

1. Disconnect the negative terminal from the battery.

2. Raise the car.
3. Remove the right rear wheel/tire.
4. Remove the engine oil cooler base assembly.
Do not disconnect the hoses.ProCarManuals.com

45N
.
m (4.5 kg-m. 33 Ib-ft)

14. Remove the connector, the terminal and the alternator.
1 5. Remove the bolt from the side engine mount, then
push the side mounting bracket into the housing of
the body (page 5-27).
16. Remove the transmission mount.
17. Remove the cylinder head covers.

18. Turn the crankshaft so that the No. 1 piston is at

top dead center (page 6-25, 26).

19.
Install
a
brace
under
the
engine, then
tilt
the
engine approximately 5° using a jack.
Timing Belt
Removal (cont'd)
BELT COVER
ALTERNATOR
20. Remove the alternator bracket stiffener.
ALTERNATOR BRACKET
STIFFENER

21. Remove the air conditioning (A/C) compressor ad-
justing pulley and belt.

22. Remove the dipstick pipe mounting bolt, then re- move the front and rear timing belt middle covers.
23. Remove the crankshaft pulley, then remove the tim- ing belt lower cover.
24. Loosen the timing belt adjusting bolt 180° and release the belt tension.
NOTE: Push the tensioner to release tension from
the belt, then retighten the adjusting bolt.
ADJUSTING BOLT
Do not remove. When

adjusting, loosen

it
180°.
25. Remove the timing belt from the pulleys.
CAUTION: Do not crimp or bend the timing belt more

than 90° or less than 25 mm (1 in.) in diameter.
DIAMETER

1.0 x
1.25
mm

45N .
m (4.5 kg-m,

33 Ib-ft)

6 x 1.0 mm

12N .
m (1.2 kg-m, 9 Ib-ft) DIPSTICK PIPE

8x1.25 mm

22N .
m

(2.2 kg-m,
16 Ib-ft)
9 Ib-ft)
6 x 1.0 mm

12N .
m (1.2 kg-m.

6 Ib-ft29

ADJUSTING BOLT

8x1.25 mm

8N .
m (0.8 kg-m,

1.0 x
1.25
mm
8x1.25 mm

12N .
m (1.2 kg-m,

9 Ib-ft)ProCarManuals.com