ACURA NSX 1991 Service Repair Manual

Cylinder Head

Camshaft

The camshaft is a cast piece. By improving dimensional accuracy, it became possible to achieve minimum space be-

tween cams, thus allowing a more compact cylinder head. Each camshaft is supported on four bearing journals with forc-

ed lubrication. On the right end of each camshaft is a driven pulley. The exhaust and intake cycles require a total of 36

cam lobes to open and close the valves.

FRONT BANK

No. 6 No. 5 No. 4

S M P S M P S M P

P M S P M S P M S
EXHAUST INTAKE

S M P S M P S M P

P M S P M S P M S
REAR BANK

No. 3 No. 2 No. 1

No. 3 No. 2 No. 1
No. 6 No. 5 No. 4
INTAKE EXHAUST

P: PRIMARY

M:MID

S: SECONDARY

: Intake valve open

: Exhaust valve open
Manual Transmission

Automatic Transmission

Low-speed valve timing

High-speed valve timingProCarManuals.com

Lubrication System

Lubrication Flow

VTEC SOLENOID VALVE

ROCKER SHAFT

ORIFICES
M
M

M

CYLINDER HEAD

ORIFICE

OIL SCREEN

OIL PUMP

RELIEF VALVE

OIL FILTER

ENGINE COOLANT

ENGINE OIL

COOLER

CYLINDER HEAD

ORIFICE

ROCKER SHAFT

ORIFICES

P: PRIMARY

M: MID

S: SECONDARY
M
M

M

VTEC SOLENOID VALVE
No. 3

M
M
M
No. 1

No. 2
M

M
M

No. 6 No. 5 No. 4
Front

Rear
CRANKSHAFT

MAIN JOURNAL

MAIN BEARING

CAP BRIDGEProCarManuals.com

Exhaust System

Dual Exhaust System

A compact dual exhaust system is used to provide low back pressure.
Sound tuning has been optimized to give a sporty exhaust sound note suitable to this type of car. This is done by a col-
lection chamber in muffler.
MUFFLER

REAR
EXHAUST

PIPE

REAR EXHAUST

MANIFOLD

FRONT THREE WAY CATALYTIC

CONVERTER

REAR THREE WAY CATALYTIC

CONVERTER

FRONT
EXHAUST

PIPE

FRONT EXHAUST

MANIFOLD

Exhaust gas
from
rear bank

COLLECTION CHAMBER

Exhaust gas

from

front bank

FeaturesProCarManuals.com

Cooling

Cooling System

Two cooling systems are employed:

An antifreeze/water system with the radiator mounted in the front of the vehicle.

An air-cooling system driven by a fan mounted in the engine compartment.

BLEEDER

RADIATOR

BLEEDER

WATER VALVE

HEATER CORE
DRAIN

DRAINS

BLEEDER

ENGINE DRAIN

WATER PUMP

ENGINE OIL

COOLER

ENGINE DRAIN

FAST IDLE THERMO VALVE

IDLE AIR CONTROL (IAC) VALVE

BREATHER PIPE

THROTTLE

BODY
THERMOSTAT
TEMPERATURE SWITCH
ENGINE COOLANT
BLEEDER
EXPANSION

TANKProCarManuals.com

Special Tools

Ref.
No.
Tool Number

07MAK-PR7020A
Description

Engine Removal/Installation Fixture
Qty

1
Page Reference

5-27ProCarManuals.com

Engine Removal/Installation

Make sure jacks and safety stands are placed proper-ly and hoist brackets are attached to the correct
positions on the engine (see section 1).
Make sure the car will not roll off stands and fall
while you are working under it. 3. Remove the expansion tank cap to speed draining.
Use care when removing the expan-
sion tank cap to avoid scalding by hot engine
coolant or steam.

4. Raise the hoist to full height.
5. Drain the engine coolant (see section 10).

STRUT BAR
10 x
1.25
mm

39 N.m (3.9 kg-m, 28 Ib-ft)
EXPANSION TANK

CAP

: CORROSION RESISTANT BOLT
(cont'dj

1. Move the seat bottoms and backs as far forward as

they will go.

2. Disconnect the battery negative terminal first, then
the positive terminal.
Loosen the drain plug from the radiator lower

tank.

Remove two drain bolts from the water pipes

Reinstall the drain bolts with new washers.

Loosen the front and rear engine drain bolts to
drain engine coolant from cylinder heads. Con-
nect rubber hoses to the drain bolts.
6. Drain transmission oil/fluid. Reinstall the drain plug using a new washer.
CAUTION: Do not overtighten the drain plug.
7. Drain the engine oil. Reinstall the drain plug using a new washer.
8. Lower the hoist.
9. Remove the strut bar.
CAUTION:
Use front and rear fender covers to avoid damaging
painted surfaces.
Unspecified items are common.Unplug the wiring connectors carefully while holding
the coupler and the connector portion to avoid damage.
Mark all wiring and hoses to avoid mis-connection.
Also, be sure that they do not contact other wiring or hoses or interfere with other parts.
If the ground clearance needs to be increased, use a
scissors jack and install the rubber spacers to the coil
springs (page 1-8).
Put rubber pads under the jacking points when using
jacks or safety stands to avoid damaging the body (page 1-9 to 11).ProCarManuals.com

Engine Removal/Installation

(cont'd)

10. Disconnect the resistor connector and fan motor connector, then remove the engine room fan
assembly.
ENGINE ROOM

FAN
ENGINE ROOM
FAN CONNECTOR
GROMMET
11. Remove the rear trim panels behind the
passenger's seat, then disconnect four connectors
from Engine Control Module (ECM) and five con- nectors from floor wire harness.
ENGINE WIRE
HARNESS CONNECTORS
ECM

PASSENGER'S

SEAT

FLOOR WIRE HARNESS
ENGINE WIRE

HARNESS

FUEL PUMP RESISTOR
CONNECTORGROUND

CABLE

6x1.0
mm

10 N.m (1.0 kg-m, 7 Ib-ft)
CORROSION RESISTANT BOLT
6 x 1.0 mm

10 N.m d.Okg.m, 7 Ib-ft)ProCarManuals.com

12. Remove the intake manifold plate and the top
cover.
13. Remove the throttle cable by loosening the locknut, then slip the cable end out of the throttle bracketand accelerator linkage.

INTAKE MANIFOLD
TOP COVER
6 x 1.0 mm

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

PLATE

ADJUSTING NUT

LOCKNUT
CABLE END

14. Relieve fuel pressure by slowly loosening the ser-
vice bolt on the fuel filter about one turn (see sec-

tion 11 ).

1 5. Remove the fuel feed pipe.
16. Remove the fuel return hose from the pressure con- trol valve.

6 x 1.0 mm

22 N .
m (2.2 kg-m. 16 Ib-ft) 12 N .
m (1.2 kg-m, 9 Ib-ft)
FUEL FEED
PIPE
WASHERS

Replace.

FUEL RETURN
HOSE

17. Disconnect two hoses, then remove the expansion tank.

6 x 1.0 mm
10 N .
m (1.0 kg-m, 7 Ib-ft)
EXPANSION TANK
WATER HOSES
(cont'd)

Do not smoke while working on the
fuel system. Keep open flame away from work
area. Drain fuel only into an approved container.
CAUTION:
THROTTLE CABLE

NOTE:

Take care not to bend the cable when removingit. Always replace a kinked cable with a new
one.
Adjust the throttle cable when installing (see
section 11).
Before disconnecting any fuel line, relieve the
fuel pressure as described above.
Place a shop towel over the fuel filter to prevent
pressurized fuel from spraying over the engine.ProCarManuals.com

Engine Removal/Installation

(cont'd)

18. Remove the breather pipe, then remove the air in- take duct and the air cleaner case.

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

CASE

BREATHER PIPE

19. Disconnect the evaporative emission (EVAP) con- trol canister hose from throttle body.
20. Disconnect the brake booster vacuum hose from the intake manifold.
EVAP CONTROL CANISTER
EVAP CONTROL

CANISTER
HOSE
BRAKE BOOSTER

VACUUM HOSE 21. Disconnect the two engine wire harness connec-
tors from the side wire harness at left side of
engine compartment, and remove the engine wireharness terminal and the starter cable terminal
from the main fuse box and clamps.
22. Remove the ground cable from the transmission. MAIN FUSE BOX
6x1.0
mm
10 N .
m
(1.0 kg-m,
7 Ib-ft)
ENGINE WIRE

HARNESS

23. Remove the water hoses and the heater hose from the water passage.
HEATER HOSE
WATER HOSES
: CORROSION RESISTANT BOLTProCarManuals.com

24. Disconnect the three connectors from the emission
control box.
6 x 1.0 mm
10 N .
m
(1.0 kg-m,
7 Ib-ft)
EMISSION CONTROL

BOX

CONNECTORS

25. Move the trunk carpet and disconnect the right rear sensor connector. Push the wire and connector
through the body hole into the engine compart-

ment.

26. Remove the front engine mounting bolt (page 5-29).
RIGHT REAR SENSOR
CONNECTOR 27. Raise hoist to full height.
28. Remove the clutch slave cylinder from the transmission case (M/T see section 12).
CONTROL LEVER
SHIFT CABLE CABLE COVER
CENTER ROD
ASSEMBLY

8x1.25
mm
22 N.m
(2.2 kg-m,
16 Ib-ft)

6x1.0
mm

8 N.m (0.8 kg-m, 6 Ib-ft)

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

UNDER GUARD

10 x
1.25
mm
60 N
.
m (6.0 kg-m, 43 Ib-ft)
(cont'd)
: CORROSION RESISTANT BOLT/NUT
Do not disconnect the vacuum hoses.
Do not disconnect the clutch hose.
29. Remove the lower cover, then remove the shift cable and select cable with cable bracket (M/T see
section 13).
30. Remove the cover, then remove the shift cable (A/T see section 14).

NOTE:
Take care not to bend the cable when removingit. Always replace a kinked cable with a new
one.
Adjust the cables when installing.
31. Remove the engine under guard and the center rod
assembly.

A/T:ProCarManuals.com