1991 ACURA NSX Service Repair Manual

Cylinder Heads

Illustrated Index (cont'd)
CAUTION:
To
avoid
damage,
wait
until
the
engine
coolant
temperature
drops
below
100°F
(39-C]
before
removing
the
cylin-

der head.

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

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

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

Troubleshooting, page 6-3 ('91-'93) or ('94-'96)

EXHAUST GAS
RECIRCULATI0N (EGR) VALVE

6 x 1 .0 mm
12 N·m
(1.2 kg-m.
9 Ib-ft)
8 x
1.25
mm

22 N·m
(2.2 kg-m,
16 Ib-ft)
ENGINE COOLANT
TEMPERATURE (ECT) SENSOR
18 N·m (1.8 kg-m, 13 Ib-ft)

8 x
1.25
mm
22 N·m (2.2 kg-m. 16 lb-ft)
FRONT VTEC SOLENOID VALVE

Troubleshooting. page 6-3

SEALING BOLTS

60 N·m
(6.0 kg-m,

43 lb-ft)

OIL PRESSURE

GAUSE SENDING
UNIT (section 23)

ROCKER

SHAFTS
WASHERS
Replace.

8 x
1.25
mm

22 N·m
(2.2 kg-m,16 Ib-ft)
DOWEL PIN

0-RING

Replace.

ECT SWITCH

28 N·m
12.8 kg-m.

20 lb-ft

O-RING

Replace.

O-RING

Replace.

ROCKER ARM ASSEMBLY[PRIMARY. MID, SECONDARY]

Inspection, page 6-32 ('91-'93) or ('94-'96)

ROCKER SHAFT

OIL CONTROL
ORIFICE

Remove with 5 mm

boit and clean.

FILTER
Replace.

GASKET

Replace.

O-RING

Replace.ProCarManuals.com

INTAKE VALV E
SPRIN G OUTE R VALV
E KEEPER S
SPRIN G RETAINE R
INTAK E VALV E
SPRIN G INNE R
CYLINDE R HEA D BOL T
11 x 1. 5 m m78 N- m (7. 8 kg-m , 5 6 Ib-ft )Apply engin e oi l t oth e bol t threads .
CYLINDE R HEA D
GASKE T
Replace . CYLINDE
R HEA D BOLT S
11 x 1.5 m78N- m (7. 8 kg-m , 5 6 Ib-ft )
Appl y engin e oi l t o
the bol t threads .
VALVE SPRIN G SEA T
EXHAUS T VALV E
SPRIN G
SPRIN G RETAINE R
VALVE KEEPER S
VALVE SEA L
VALV E GUID E
LOS T MOTIO N
ASSEMBL Y
Test , 6-3 2
CYLINDE R HEA D
GASKE TReplace .
DOWEL PI N
OI L CONTRO L ORIFIC E
Remov e wit h 6 m m
bol t an d clean .
O-RING S
Replace . CYLINDE
R HEA D ORIFIC ERemove wit h 6m mbolt an d clean .
VALVE SEA L
VALV E GUID E
LOS T MOTIO N
ASSEMBL Y VALV
E SPRIN GSEAT
EXHAUS T VALV E
INTAK E VALVE
DOWEL PIN S
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Cylinder Heads

Removal

Engine removal is not required for this procedure. Make sure jacks and safety stands are
placed properly and hoist brackets ere attached to cor- rect positions on the engine.
CAUTION: Use a fender cover (special tool) to avoid damaging
painted surfaces. Unplug the wiring connectors carefully while holding
the connector portion to avoid damage.
To avoid damaging the cylinder heads, wait until the
engine coolant temperature drops below 100°F
(38°C) before loosening the retaining bolts. Do not open the engine cover when the roof panel is
stored (NSX-T open top).
NOTE:
Unspecified items are common.

Mark all wiring and hoses to avoid misconnection.
Also, be sure that they do not contact other wiring or

hoses or interfere with other parts.

Inspect the timing belt before removing the cylinder

head.

Turn the crankshaft pulley SO that the No. 1 piston is at top dead center (see page 6-19 ('91-'93) or ('94-'96)).
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, then remove the right rear wheel/tire.
4. Drain the engine coolant (see page 10-5 ). 5. Remove the engine under guard, then remove the
front exhaust pipe A.

GASKETS
Replace.

FRONT EXHAUST

PIPE A

SELF-LOCKING NUT

10 x
1.25
mm

55 N·m (5.5 kg-m, 40 Ib-ft)
Replace.
SELF- LOCKING NUT

8 x
1.25
mm

22 N·m (2.2 kg-m. 16 Ib-ft)

Replace.

6. Remove the rear exhaust pipe A.

SELF- LOCKING NUT

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

Replace.

REAR

EXHAUST

PIPE A

SELF-LOCKING NUT
10 x
1.25
mm

55 N·m (5.5 kg-m.

40 Ib-ft)

Replace.
GASKETS

Replace.

7. Remove the engine oil cooler base assembly (see
page 6-15 ('91-'93) or ('94-'96).

8. Lower the car.
9. Remove the strut brace (see page 5-3 ).ProCarManuals.com

10. Remove the engine cover stay from the strut brace,
then set the engine cover stay between the engine
cover and rear hatch latch (NSX-T open top),
CAUTION: Use a shop tower to avoid damaging

painted surfaces.

SHOP

TOWEL

11. Relieve fuel pressure by loosening the service bolt on the fuel filter about one turn (see section 11).
Do not smok* while working on fuel
system; Keep open flame or spark away from work

area. Drain fue1 only into an approved container.

12. Remove the fuel feed pipe and fuel return hose (see page 5-5 ('91-'93) or ('94-'96).

13. Remove the evaporative emission (EVAP) control
canister hose and brake booster vacuum hose (see
page 5-5 ('91-'93) or ('94-'96).
14. Disconnect the breather pipe and vacuum hose, then remove the air cleaner housing.

6 x 1.0 mm

10 N·m (1.0 kg-m, 7 lb-ftl

AIR CLEANER
HOUSING

BREATHER

PIPE

: CORROSION RESISTANT BOLT
15. Remove the Hoses, then remove the expansion tank
(see page 5-5 ('91-'93) or ('94-'96).
16. Removel the radiator hoses and heater hose (see
page 5-6 ('91-'93) or ('94-'96).

17. Disconnect the two connectors, then remove the
control box (see page 5-6 ('91-'93) or ('94-'96).

18. Remove the intake manifold plate and top cover.

INTAKE MANIFOLD

PLATE
6 x
1.0mm

12 N·m (12kg-m,

9 lb-ft)

TOP COVER

19. Remove the fuel injector covers.
6 x 1.0 mm
12 N·m (1-2 kg-m, 9 lb-ft)

FUEL INJECTOR

COVER

(cont'd)

ENGINE

COVER

STAYProCarManuals.com

Cylinder Head s
Remova l
20. Remov e th e breathe r hos e an d wate r bypas s hoses .
BREATHE RHOSE
WATE R BYPAS S
HOSE S
21. Remov e th e ignitio n coi l cove r an d harnes s cover .
6 x 1. 0 m m10 N- m (1. 0 kg-m ,7 Ib-ft )
IGNITIO N COI LCOVER .
HARNES S COVE R
22. Remov e th e positiv e Crankcas e ventilatio n (PCV )
hose , vacuu m hos e an d harnes s clamp .
6 x 1. 0 m m10 N- m (1. 0 kg-m , 7 Ib-ft )
PCV HOS E
VACUU M HOS E
23. Remov e th e harnes s cover s an d groun d cable s fro m
th e intak e manifold .
GROUND CABL E6 x 1. 0 m m12 N- m (1. 2 kg-m , 9 Ib-ft )
GROUN D CABL E
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24. Remove the engine wire harness connectors and
wire harness clamps from the cylinder head and
intake manifold, Six injector connectors
Intake air temperature (IAT) sensor connector
CKP/CYP sensor connector
Heated oxygen sensor (HO2S) connectors

Ignition control module (ICM) connectors

Engine coolant temperature (ECT) sensor connec-

tor

ECT gauge sending unit connector
ECT switch connector
Exhaust gas recirculation (EGR) valve lift sensor

connector

Throttle position sensor connector Engine oil pressure gauge sending unit connector
Knock sensor connector
VTEC solenoid valve connectors
VTEC pressure switch connectors
Engine oil pressure switch connector
Alternator connector

Alternator terminal

Throttle body 6P connector

25. Remove the ignition coils and connector.

26. Remove the EGR pipe and intake manifold assem- bly.

8 x 1.25mm

22 N·m (2.2 kg-m, 16 Ib-ft)

6 x 1.0 mm
12 N·m
(1.2 kg-m,

9 lb-ft)

GASKETS

Replace. INTAKE
MANIFOLD
ASSEMBLY

GASKET
Replace.
27. Loosen the adjusting nut and idler pulley center nut,
then remove the air conditioning compressor belt

(see page 6-17('91-'93) or ('94-'96)).

28. Remove the cover, adjusting bolt, mounting bolt and mounting nut, then remove the alternator belt
and alternator.

COVER

MOUNTING BOLT
10 x
1.25
mm

45 N·m (4.5 kg·m,

33 Ib-ft)

MOUNTING NUT
10 x
1.25
mm

45 N·m (4.5 kg·m.

33 Ib·ft)
ALTERNATOR

BELT

29. Disconnect the knock sensor connector, then remove
the wire holder.

6 x 1.0 mm
12N·m (1.2 kg-m, 9 Ib-ft)

KNOCK SENSOR
WIRE HOLDER
(cont'd)

6 x 1.0 mm

12 N·m (1.2 kg-m, 9 Ib-ft)

ADJUSTING

BOLTProCarManuals.com

Cylinder Heads

Removal (cont'd)
30. Remove the water passage. \
\
32. Remove the alternator bracket stiffener (see page 6-16
('91-'93) or ('94-'96).
33. Remove the alternator bracket.

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

ALTERNATOR
BRACKET

10 x
1,25
mm

45N·m (4.5 kg-m,

33 Ib-ft)

34. Remove the timing belt (see page 6-15 ('91-'93) or ('94-'96)).

the timing belt

35. Remove the camshaft pulleys.

RETAINING

BOLTS
CAMSHAFT PULLEYS

GROUND

CABLE

WASHER

CYLINDER HEAD

COVER

31. Remove the cylinder head covers.
0-RINGS

Replace.

CONNECTING PIPE

WATER PASSAGE

8 x 1.25 mm

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

36. Remov e th e fron t an d rea r bac k covers .
REAR BAC K
COVE R
RUBBER SEAL S
FRON T BAC K
COVE R
37. Loose n th e rocke r ar m locknut s an d th e adjustin g
screws .
38. Remov e th e camshaf t holde r plates , camshaf t holder s
and camshafts .
FRONT INTAK ECAMSHAF T
CAMSHAFT HOLDE R
PLATE S
RUBBE R SEA L
FRON T EXHAUS TCAMSHAF T
OIL SEAL S
Replace .
39. Remov e th e cylinde r hea d bolts , the n remov e th e
cylinde r head .
CAUTION : T o preven t warpage , unscre w th e bolt s
i n sequenc e 1/ 3 tur n a t a time ; repea t th e sequenc e
unti l al l bolt s ar e loosened .
CYLINDE R HEA D BOLT S LOOSENIN G SEQUENC E
NOTE : Separat e th e cylinde r hea d fro m th e bloc k
with a fla t blad e screwdrive r a s shown .
40. Remov e th e fron t an d rea r exhaus t manifold s (se e
page 9-4 ).
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