ACURA NSX 1991 Service Repair Manual

Installation

CAUTION: Do not rotate the crankshaft or camshaft without installing the belt. The piston could hit a valve
and damage may result.
1 . Install the timing belt in the reverse order of removal; Only keypoints are described here.
2 . Remove all spark plugs.
3. Position the crankshaft and the camshaft pulley as shown before installing the timing belt.
A Set the crankshaft so that the No. 1 piston is at top dead center (TDC).NOTE: Turn the crankshaft until its keyway
is facing up.
B Align the TDC mark on the front exhaust camshaft pulley and front intake camshaftpulley to the pointer on the front timing belt
cover plate.
C Align the TDC mark on the rear intake cam-
shaft pulley to the pointer on the rear timing
belt cover plate.
D Align the rear exhaust camshaft pulley one half tooth clockwise past TDC.
POINTER ON REAR
COVER PLATE
REAR EXHAUSTCAMSHAFT PULLEY

TIMING BELT
DRIVE PULLEY
(CRANKSHAFT)
FRONT EXHAUST

CAMSHAFT PULLEY

(cont'd)
5. Tension the timing belt between the pulleys in the
sequence A to E as shown above.
4. Install the timing belt in the sequence shown.

FRONT INTAKE
CAMSHAFT PULLEY
REAR INTAKE
CAMSHAFT PULLEY
Rear exhaust camshaft pulley.
Timing belt drive pulley (crankshaft)

Ad-

Water

justing pulley
Front intake camshaft pulley Front exhaust camshaft pulley
pump pulley Rear intake camshaft pulley Refer to page 6-22 for timing belt tension ad-

justment.ProCarManuals.com

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 pre-
vent the rubber seal from falling off.
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.
8. If the camshaft pulleys are not positioned at TDC,

remove the timing belt and adjust the positioning of

the pulleys, then reinstall the timing belt.

6. Temporarily install the lower cover and crankshaft

pulley.

7. Check the crankshaft pulley and the camshaft pulleys at TDC.
FRONT:
5.0 mm

PIN PUNCHES

MIDDLE COVER

REAR:

TDC MARK

5.0 mm

PIN PUNCHES
Direction
of rotation.
FRONT:

REAR:

TDC MARK

TDC MARK

(White paint)

TDC MARKS

COVER PLATE

TDC MARK

MIDDLE COVER TDC MARKS

Timing Belt
Installation (cont'd)


Refer to page 6-23, 24 for timing belt removal.
Bring the "UP" mark of the camshaft pulleys to
the top, and align the TDC marks on the pulleys.
Align the holes on the camshaft holder pipes to
the camshaft holes, insert 5.0 mm pin punches
and fix them at TDC.

Remove the pin punches after the timing belt has
been reinstalled.

NOTE:

NOTE:ProCarManuals.com

Crankshaft Position (CKP)/Cylinder Position
(CYP) Sensor
NOTE: Turn the crankshaft so that the No. 1 piston is
at top dead center (page 6-25, 26).

1. Remove the timing belt (page 6-23, 24).

2. Remove the front intake and exhaust camshaft
pulleys.

3. Remove the front timing belt cover plate.
4. Remove the CKP/CYP sensor from the front cylinder head. 5. Install the CKP/CYP sensor in the reverse order of
removal;

Replacement

FRONT INTAKE
CAMSHAFT PULLEY

10 x
1.25
mm

70N .
m (7.0 kg-m,

51 Ib-ft)

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

6 x 1.0 mm
12N .
m (1.2 kg-m,
9 Ib-ft) TIMING BELT
LOWER COVER TIMING BELT
MIDDLE COVER
FRONT TIMING

BELT COVER PLATE

10 x
1.25
mm

70N .
m (7.0 kg-m,

51 Ib-ft) FRONT EXHAUST
CAMSHAFT PULLEY
TIMING

BELT

FRONT

CAMSHAFTS

CKP/CYP

SENSOR

Refer to page 6-25 and 26, when installing the

timing belt.ProCarManuals.com

Cylinder Heads

Removal

Engine removal is not required in this procedure.
CAUTION: To avoid damaging the cylinder heads, wait until the engine coolant temperature drops below 100°F (38°C) before loosening the retaining bolts.

NOTE:
Inspect the timing belt before removing the cylinder
heads.
Turn the crankshaft so that the No. 1 piston is at top
dead center (TDC (page 6-25, 26). Mark all emission hoses before disconnecting them.
1. Disconnect the negative terminal from the battery.
2. Remove the expansion tank cap.
Use care when removing the expan-
sion tank cap to avoid scalding by engine coolant or

steam.

3. Raise the car.
4. Remove the right rear wheel/tire.
5. Remove the engine under guard, then remove the front exhaust pipe.
6. Remove the rear exhaust pipe.
CAUTION: Do not use an air wrench or hammer to
remove or install the exhaust system unless you
first remove the heated oxygen sensors.

GASKETS

Replace.

FRONT EXHAUST

PIPE

SELF-LOCKING NUTS

10 x
1.25
mm

34N .
m (3.4 kg-m, 25 Ib-ft)

Replace.
REAR EXHAUST

PIPE

SELF-LOCKING NUTS

10 x
1.25
mm

34N .
m (3.4 kg-m, 25 Ib-ft)

Replace.

GASKETS
Replace.

7. Remove the under cover, then remove the water pipe drain bolts and drain the engine coolant.
8. Attach the hoses to front and rear engine drain bolts, then loosen the bolts and drain the engine
coolant.
Bleed air from the cooling system when install-
ing the cylinder heads (page 10-5).
9. Remove the engine oil cooler base assembly (page
6-23).

10. Lower the car.
11. Remove the strut bar (page 5-19).
12. Remove the intake manifold plate and top cover (page 5-21).
13. Remove the throttle cable by loosening the locknut, then slip the cable and nut off the throttle bracketand throttle link (page 5-21).

NOTE:
Take care not to bend the cable when removingit. Always replace a kinked cable with new one.Adjust throttle cable when installing (see sec-

tion 11).ProCarManuals.com

14. Relieve fuel pressure (see section 11).
Do not smoke while working on fuel
system; keep open flame or spark away from work
area. Drain fuel only into an approved container.
1 5. Disconnect the fuel feed pipe and the return hose
(page 5-21).

16. Remove the ignition coil covers, the wire harness covers, the ignition coils and the connectors (page
6-23).
17. Remove the water hoses, then remove the expan- sion tank (page 5-21).
18. Remove the breather hose, and the air cleaner housing (page 5-22).
19. Remove the brake booster hose, the evaporative emission (EVAP) control canister hose and other
hoses from the intake manifold and throttle body
(page 5-22).
20. Remove the emission control box (page 5-23). Do not disconnect emission hose.Disconnect the three connectors before
removing.
21. Remove the connector, the terminal and the alternator.
22. Disconnect the following engine wire harness con- nectors, then remove the harness clamps from thecylinder head and the intake manifold.
Front cylinder head:

Crankshaft position (CKP)/cylinder position
(CYP) sensor connector
Air conditioning (A/C) compressor magnetic clutch connector
Heated oxygen sensor (H02S) connector
Ground cable terminals Three injector connectors (cylinders No. 4, 5

and 6)

Intake air temperature (IAT) sensor connector
Ignition control module (ICM) connector
Condenser connector

Engine oil pressure gauge sending unit

connector

VTEC solenoid valve connector
VTEC pressure switch connector
Engine coolant temperature (ECT) sensor

connector
ECT sending unit connector
Accelerator pedal opening sensor connector

(throttle body)

Radiator fan control sensor connector
Rear cylinder head: Engine oil pressure switch connector (oil cooler

base)

Heated oxygen sensor connector
Three injector connectors (cylinders No. 1, 2

and 3)
Idle air control (IAC) valve connector
Knock sensor connector
Throttle actuator motor connector

Throttle position sensor connector

VTEC solenoid valve connectorVTEC pressure switch connector
ICM connector

Ground terminal

ICM CONNECTORS THROTTLE ACTUATOR

MOTOR CONNECTOR

THROTTLE POSITION
SENSOR CONNECTOR
ACCELERATOR PEDAL OPENING
SENSOR CONNECTORProCarManuals.com

Cylinder Heads
Removal (cont'd)
23. Remove the exhaust gas recirculation (EGR) pipe and the intake manifold assembly.
NOTE: Fill the cylinder head intake ports with clean
shop towels to prevent foreign materials from get-

ting into the cylinders.

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

16 Ib-ft)

EGR PIPE MOUNTING BOLT

6 x 1.0 mm

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

GASKET
Replace. INTAKE MANIFOLD

GASKET

Replace.
GROUND CABLE

6 x 1.0 mm
12N .
m (1.2 kg-m,
9 Ib-ft)
POSITIVE CRANKCASE VENTILATION
(PCV) HOSE
Remove.

IAT SENSOR
CONNECTORINJECTOR CONNECTOR
(No. 4 CYLINDER)
GROUND

CABLE

INJECTOR CONNECTOR
(No.1 CYLINDER)ProCarManuals.com

(cont'd)
29. Remove the water passage.

O-RINGS
Replace.
CONNECTING PIPE
WATER PASSAGE

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

30. Remove the cylinder head covers.
31. Turn the crankshaft so that the No. 1 piston is at top dead center (page 6-25, 26).

32.
Install
a
brace
under
the
engine, then
tilt
the
engine approximately 5° using a jack (page 6-24).
33. Remove the alternator bracket.
8 x
1.25
mm

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

10 x
1.25
mm

45N.m (4.5 kg-m.

33 Ib-ft)

ALTERNATOR
BRACKET

24. Remove the bolt from the side engine mount, then
push the side mounting bracket into the housing of
the body (page 5-27).
25. Remove the transmission mount. 26. Remove the alternator bracket stiffener (page 6-24).
27. Disconnect the knock sensor connectors, then re- move the wire holder.

6 x 1.0 mm
12N .
m (1.2 kg-m. 9 Ib-ft)
KNOCK SENSOR
WIRE HOLDER
28. Remove the heater hose and the water hoses.
WATER HOSES
HEATER HOSEProCarManuals.com

Cylinder Head

Removal (cont'd)

34. Remove the A/C compressor adjusting pulley and

belt.

33. Remove the dipstick pipe mounting bolt, then re-

move the front and rear timing belt middle covers.

35. Remove the crankshaft pulley, then remove the tim-

ing belt lower cover.

36. 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.

Loosen it 180°.

37. 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.

FRONT TIMING BELT

COVER PLATE
RUBBER SEALS
39. Remove the front and rear timing belt cover plates.

REAR TIMING BELT

COVER PLATE
RETAINING

BOLTS

CAMSHAFT PULLEYS
38. Remove the camshaft pulleys.

A/C compressor adjusting pulley and A/C com-

pressor belt

Timing belt lower cover

Crankshaft pulley
NOTE: Removal of the following items is not necessary

if only the rear cylinder head is going to be removed.ProCarManuals.com

40. Loosen the valve locknuts and the adjusting

screws.

41. Remove the camshaft holder pipes, the camshaft

holders and the camshafts.

CAMSHAFT HOLDER

PIPES

FRONT INTAKE

CAMSHAFT

RUBBER SEAL

FRONT EXHAUST

CAMSHAFT

OIL SEALS

Replace.

42. Screw a 5 mm bolt into each rocker shaft orifice,

then pull out the rocker shaft orifices.

ROCKER SHAFT

ORIFICE

O-RING

Replace.
5 mm BOLT

O-RING

Replace.

(cont'd)
12 mm BOLT
12 mm BOLT
ROCKER ARM

ASSEMBLY
RUBBER BAND
SEALING VTEC VALVE

BOLT

45. Bundle the rocker arms with rubber bands to keep

them together as sets.

46. Screw a 12 x 1.25 mm bolt into each rocker

shaft. Remove the rocker arms while slowly pull-

ing the rocker shafts out of the cylinder heads

toward the transmission.
FILTER

Replace.
WASHER

Replace.
43. Remove the VTEC valve assemblies.

44. Remove the sealing bolts.

WASHER

Replace.

SEALING BOLTProCarManuals.com

Cylinder Heads

Removal (cont'd)

47. Disconnect the connectors and remove the engine

wire harness.

48. Remove the cylinder head bolts, then remove the

cylinder heads.

CAUTION: To prevent war page, unscrew the bolts

in sequence 1 /3 turn at a time; repeat the sequence

until all bolts are loosened.

CYLINDER HEAD BOLTS LOOSENING SEQUENCE

49. Remove the front and rear exhaust manifold covers,

then remove the front and rear exhaust manifolds.

CAUTION: Do not use an air wrench or hammer to

remove the exhaust system unless you first remove

the heated oxygen sensor.
NOTE: Separate the cylinder head from the block with

a flat blade screwdriver as shown.ProCarManuals.com