ACURA NSX 1991 Service Repair Manual

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

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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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Rocker Arm s an d Shaft s
Remova l
1. Scre w a 5 m m bol t int o eac h rocke r shaf t oi l contro l
orifice , the n pul l ou t th e rocke r shaf t oi l contro l ori -
fices .
ROCKE R SHAF T
OI L CONTRO L
ORIFIC E
Clean . 5
m m BOL T
O-RIN G
Replace .
O-RING
Replace .
2. Remov e th e VTE C solenoi d valve , the n remov e th e
sealin g bolts .
WASHE R
Replace .
SEALIN G BOL T
WASHE R
Replace .
FILTER/O-RIN G
Replace .
SEA IN G VTE C SOLENOI D VALV E
BOL T
3. Bundl e th e rocke r arm s wit h rubbe r band s t o kee p
the m togethe r a s sets .
4 . Scre w a 1 2 x 1.2 5 m m bol t int o eac h rocke r shaft .
Remov e th e rocke r arm s whil e slowl y pullin g th e
rocke r shaft s ou t o f th e cylinde r head s towar d th e
transmissio n end .
ROCKE R AR M
ASSEMBL Y RUBBE
R BAN D
12 m m BOL T
1 2 m m BOL T
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Locations
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.

NOTE:
Identify parts as they are removed to ensure reinstallation in priginal locations.

Inspect rocker shafts and rocker arms (see pages 6-32 ('91-'93) or ('94-'96) and 33 ('91-'93) or ('94-'96) .
Rocker arms must be installed in the same position if reused.
Adjust 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.

SEALING BOLTS 20 mm
60 N·m (6.0 kg-m, 43 Ib-ftl EXHAUST ROCKER

SHAFT

WASHERS

Replace.
INTAKE ROCKER

SHAFT

Rear Cylinder Head:

SEALING BOLTS 20 mm
6
0
N·m (6.0 kg-m, 43 Ib-ft)

INTAKE ROCKER

SHAFT

WASHERS
Replace. EXHAUST ROCKER
SHAFT INTAKE ROCKER ARM ASSEMBLIES RUBBER BAND
RUBBER BAND
CYLINDER NUMBER
CYLINDER NUMBER
RUBBER BAND
RUBBER BAND
EXHAUST ROCKER ARM ASSEMBLIES EXHAUST ROCKER ARM ASSEMBLIES

Front Cylinder Head:ProCarManuals.com

Rocker Arm s an d Los t Motio n Assemblie s
Inspection
NOTE: Whe n reassemblin g th e primar y rocke r arm , care -
full y appl y ai r pressur e t o th e oi l passag e o f th e rocke r
arm.
PRIMAR Y ROCKE R AR M
MI D ROCKE R AR M
SECONDAR Y
ROCKE R AR M
PISTON S
Inspect th e rocke r ar m pistons . Pus h the m manually .
— If the y d o no t mov e smoothly , replac e th e rocke r
ar m assembly .
PRIMARYMID
SECONDAR Y
Check pisto n movemen t
NOTE:
• Appl y oi l t o th e piston s whe n reassembling .
• Bundl e th e rocke r arm s wit h rubbe r band s t o
kee p the m togethe r a s sets . 2
. Remov e th e los t motio n assembl y fro m th e cylinde r
hea d an d inspec t it . Pushin g i t gentl y wit h th e finge r
wil l caus e i t t o sin k slightly . Increasin g th e forc e o n
i t wil l caus e i t t o sin k deeper .
— If th e los t motio n assembl y doe s no t mov e
smoothly , replac e it .
Pus h
LOS T MOTIO N ASSEMBL Y
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Rocker Arm s an d Shaft s
Clearanc e
Measure bot h th e intak e rocke r shaft s an d exhaus t rocke r
shafts .
1 . Measur e diamete r o f shaf t a t firs t rocke r location .
MICROMETE R
Surface shoul d b e smooth .
2. Zer o gaug e t o shaf t diameter .
MICROMETE R
CYLINDER BOR EGAUG E
3. Measur e insid e diamete r o f rocke r arm , an d chec k fo r
out-of-roun d condition .
Rocke r Arm-to-Shaf t Clearanc e (Intak e an d Exhaust) :
Standar d (New) :
Primar y an d Secondary :
0.025-0.052 m m (0.0010-0.002 0 in )
Mid :
0.024-0.05 3 m m (0.0009-0.002 1 in )
Servic e Limit : 0.0 8 m m (0.00 3 in )
Inspec t rocke r ar mfac e fo r wear .
Repea t fo r al l rockers .
— If ove r limit , replac e rocke r shaf t an d al l over -
toleranc e rocke r arms .
NOTE : I f an y rocke r ar m need s replacement , replac e
al l thre e rocke r arm s i n tha t se t (primary , mid , an d
secondary) .
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Camshafts
Inspection
NOTE:
• D o no t rotat e th e camshaf t durin g inspection .
• Remov e th e rocke r arm s an d rocke r shafts .
1 . Pu t th e camshafts , th e camshaf t holder s an d holde r
plate s o n th e cylinde r head , an d the n tighte n th e bolt s
t o th e specifie d torque .
NOTE : Appl y clea n engin e oi l t o 8 m m bol t threads .
Specifie d torque :
8 m m x 1.2 5 m m bolts :
22N- m (2. 2 kg-m , 1 6 Ib-ft )
6 m m x 1. 0 m m bolts :
10N- m (1. 0 kg-m , 7 Ib-ft )
CAMSHAF T HOLDE R BOLT S TORQU E
SEQUENCE
FRONT :
2. Sea t th e camshaf t b y pushin g i t towar d th e lef t en d o f
cylinde r head .
3 . Zer o th e dia l indicato r agains t th e lef t end , the n pus h
th e camshaf t bac k an d forth , an d rea d th e en d play .
Camshaf t En d Play :
Standar d (New) : 0.05—0.1 5 m m
(0.002—0.006 in)
Servic e Limit : 0. 5 m m (0.0 2 in )
4 . Remov e th e bolts , the n remov e th e camshaf t holder s
fro m th e cylinde r head .
— Lif t th e camshaft out o f th e cylinde r head , wip e i t
clean , the n inspec t th e lif t ramps . Replac e th e
camshaft if lobe s ar e pitted , scored , o r excessivel y
worn.
— Clea n th e camshaf t bearin g surface s i n th e cylin -
de r head , the n se t th e camshaf t bac k in place .
— Inser t a plastigag e stri p acros s eac h journal.
5 . Instal l th e camshaf t holders , an d the n tighte n th e
bolt s t o th e specifie d torqu e a s show n i n th e lef t
colum n o n thi s page .
6 . Remov e th e camshaf t holder s an d measur e wides t
portio n o f plastigag e o n eac h journal .
Camshaft-to-Holde r Oi l Clearance :
Standar d (New) :
0.050-0.08 9 mm
(0.002-0.00 4 in)
Servic e Limit : 0.1 5 m m (0.00 6 in )
PLASTIGAG E STRI P
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7. If camshaft-to-holder oil clearance is out of

tolerance:

— 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) max.

Service Limit: 0.04 mm (0.0016 in)

Rotate camshaft

while measuring

— If the 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 oil clearance is still

out of tolerance, replace the cylinder head.

8. Check cam lobe height wear.

Cam Lobe Height Standard (New):

M/T

A/T
Check this area for wear.

Cam position

P: Primary M: Mid S: Secondary

FRONT BANK

REAR BANK
CYLINDER

NUMBER

EXHAUST

INTAKE

CYLINDER

NUMBER

INTAKE

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