1991 ACURA NSX lock

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

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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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

EXHAUSTProCarManuals.com

Reaming
NOTE: Fo r ne w valv e guide s only .
1 . Coa t bot h reame r an d valv e guid e wit h cuttin g oil .
2 . Rotat e th e reame r clockwis e th e ful l lengt h o f th e
valv e guid e bore .
3 . Continu e t o rotat e th e reame r clockwis e whil e
removin g i t fro m th e bore .
4 . Thoroughl y was h th e guid e i n detergen t an d wate r
t o remov e an y cuttin g residue .
5 . Chec k clearanc e wit h a valv e (se e pag e 6-39 ).
— Verif y tha t th e valv e slide s in th e intak e an d exhaus t
valv e guide s withou t exertin g pressure .
VALVE GUID E
REAMER , 5. 5 m m
07HAH-PJ7010 B
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Cylinder Head s
Installatio n
Install th e cylinde r head s in th e revers e orde r o f removal :
• Alway s us e ne w hea d gaskets .
• Cylinde r head s an d engin e bloc k surfac e mus t b e
clean .
• Tur n th e crankshaf t s o tha t No . 1 pisto n i s a t TD C
(se e pag e 6-19 ).
• D o no t us e th e middl e cove r an d lowe r cove r fo r
storin g remove d items .
• Clea n th e middl e cove r an d lowe r cove r befor e
installation .
1 . Instal l th e fron t an d rea r exhaus t manifold s t o eac h
cylinde r head , the n tighte n th e self-lockin g nut s i n a
crisscros s patter n i n tw o o r thre e steps , beginnin g
with th e inne r nut .
• Appl y oi l t o th e self-lockin g nu t threads .
• Alway s us e ne w exhaus t manifol d gaskets .
2 . Instal l th e exhaus t manifol d covers .
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Cylinder Head s
Installatio n
Rear:
8 x 1.2 5 mm22 N- m (2. 2 kg-m ,16 Ib-ft ) REA
R PRIMAR Y
HO2S45 N- m (4. 5 kg-m ,33 Ib-ft )
B e carefu l no t t o damage .
GASKE T
Replace .
REA R EXHAUS T
MANIFOLD
EXHAUSTMANIFOL DCOVER
SELF-LOCKIN G NU T8 x 1.2 5 mm34 N- m (3. 4 kg-m ,25 Ib-ft )Replace .
Install th e cylinde r head s o n th e engin e block .
Th e cylinde r hea d dowe l pin s an d th e hea d oi l con -
tro l orific e mus t b e aligned .
• Alway s us e a ne w cylinde r hea d gasket .
• Clea n th e oi l contro l orific e befor e installing .
CYLINDE R HEA D OI L CONTRO L CYLINDE R HEA D
GASKE T ORIFICE S GASKE T
Replace . Clean . Replace .
DOWE L PI N DOWE
L
PIN S
O-RIN G
Replace .
4. Tighte n th e cylinde r hea d bolt s sequentiall y i n tw o
o r thre e steps .
• Appl y clea n engin e oi l t o th e bol t thread s an d
washe r contac t surfaces .
Specifie d Torqu e
11 x 1. 5 m m
78 N- m (7. 8 kg-m , 5 6 Ib-ft )
NOTE : W e recommen d usin g a beam-typ e torqu e
wrench . Whe n usin g a preset-typ e torqu e wrench ,
b e sur e t o tighte n slowl y an d no t t o over-tighten .
CYLINDE R HEA D BOLT S TORQU E SEQUENC E
CYLINDER HEA D BOL T11 x 1. 5 m m78 N- m (7. 8 kg-m , 5 6 Ib-ft )Apply clea n engin e oi l t o th ebolt thread s an d washe r contac tsurfaces .
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Camshafts
Installation
CAUTION : Valv e locknut s shoul d b e loosene d an d ad -
justin g screw s backe d of f befor e installation .
1 . Afte r wipin g dow n th e camshaf t an d journal s i n th e
cylinde r head , lubricat e bot h surface s an d instal l th e
camshaft s an d rubbe r caps.
NOTE : Appl y liqui d gaske t aroun d th e rubbe r cap .
2 . Tur n th e camshaft until it s keywa y i s facin g up . (No . 1
cylinde r TDC) .
3 . Se t a ne w O-rin g an d a dowe l pi n i n th e oi l passag e
o f th e No . 1 camshaf t holder .
4 . Instal l th e camshaf t seal s wit h th e ope n sid e
(spring ) facin g in .
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NOTE: Ne w ro d bearing s mus t b e selecte d b y matchin g
connectin g ro d assembl y an d crankshaf t identificatio n
markings (se e pag e 7-8 ).
TIMIN GBELTSIDE
CAUTION :
• Th e pisto n skir t i s coate d wit h molybdenum ;
handle th e pisto n carefull y t o preven t an y
damage .
• Th e connectin g rod s ar e mad e o f titanium . At -
temptin g t o remov e th e pisto n pi n wit h conven -
tional sho p equipmen t wil l damag e th e connec -
ting rod .
• I f th e piston , connectin g rod , o r pisto n pi n re -
quir e replacement , al l thre e mus t b e replace d a s
an assembly .
PISTONInspection , pag e 7-13NOTE :• Befor e removin g piston , inspec t th e to pof th e cylinde r bor e fo r carbo n build-u p
o r ridge . Remov e ridg e i f necessary , pag e 7-9 .
• T o maintai n prope r pisto n clearance , matc hthe lette r o n th e pisto n to p (N o lette r denote s A. )with th e lette r fo r eac h cylinde r stampe d o n th eblock .
CONNECTIN G RO D ASSEMBL Y
En d play , pag e 7- 6
Selection , pag e 7-1 4
CONNECTIN G RO D
BEARING SClearance , pag e 7- 7
Selection , pag e 7- 8
CONNECTIN G RO D
WASHE R
CONNECTIN G RO D CA P NU T8 x 0.75 mm20 N- m (2. 0 kg-m , 1 4 Ib-ft )then tur n 95 °Afte r torquin g eac h bearin g
cap , rotat e crankshaf t t o
chec k fo r binding .
CYLINDE R BOR E SIZE SNOTE : T o maintai n prope r pisto n clearance ,match thes e letter s wit h th e letter s o n th epistons . Th e letter s o n th e bloc k rea d fro mleft t o right , No . 1 throug h No . 3 . cylinder son th e firs t lin e an d No . 4 throug h No . 6cylinder s o n th e secon d line .
CONNECTIN G RO D BEARIN G CA P
Installation , pag e 7-1 8 to 7-2 1NOTE : Instal l cap s s o th e bearin g reces s i s
o n th e sam e sid e a s th e reces s i n th e rod . PISTO
N RING S
Replacement , pag e 7-1 5
Measurement , page s 7-1 5 an d 7-1 6
Alignment , pag e 7-1 6
CONNECTIN G RO D BOL T
Inspec t to p o f eac h cylinde r bor e
for carbo n build-u p o r ridg ebefor e removin g piston .Remov e ridg e i f necessary , pag e 7- 9
ENGIN E BLOC K
Cylinde r bor e inspection , pag e 7-12
Warpag e inspection , pag e 7-12
Cylinde r bor e honing , pag e 7-13
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