1991 ACURA NSX Service Repair Manual

(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

RUBBER BAND
WASHERS EXHAUST ROCKER
Replace. SHAFT INTAKE ROCKER

SHAFT

Rear Cylinder Head:

SEALING BOLTS 20 mm60N .
m (6.0 kg-m, 43 Ib-ft) INTAKE ROCKER
SHAFT
WASHERS
Replace. EXHAUST ROCKER
SHAFT
Front Cylinder Head:
SEALING BOLTS 20 mm
60N .
m (6.0 kg-m, 43 Ib-ft)
RUBBER BAND
EXHAUST ROCKER ARM ASSEMBLIES

Rocker Arms and Shafts

Locations

Identify parts as they are removed to ensure reinstallation in original locations.
Inspect rocker shafts and rocker arms (pages 6-36 and 37).
Rocker arms must be installed in the same position if reused.
Install 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.
RUBBER BAND
CYLINDER NUMBER
CYLINDER NUMBER
RUBBER BAND

NOTE:

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.

EXHAUST ROCKER ARM ASSEMBLIESINTAKE ROCKER ARM ASSEMBLIESProCarManuals.com

Rocker Arms and Lost Motion Assemblies

Inspection

NOTE: When reassembling the primary rocker arm, care-

fully apply air pressure to the oil passage of the rocker

arm.

PRIMARY ROCKER ARM

MID ROCKER ARM

SECONDARY

ROCKER ARM

PISTONS

1. Inspect the rocker arm pistons. Push them

manually.

PRIMARY

MID

SECONDARY

Apply oil to the pistons when reassembling.

Bundle the rocker arms with rubber bands to

keep them together as sets.
LOST MOTION ASSEMBLY
2. Remove the lost motion assembly from the cylinder

head and inspect it. Pushing it gently with the finger

will cause it to sink slightly. Increasing the force on

it will cause it to sink deeper.

Push

NOTE:
Check piston movement
If they do not move smoothly, replace the rocker

arm assembly.
If the lost motion assembly does not move

smoothly, replace it.ProCarManuals.com

Rocker Arms and Shafts
Clearance
Measure both the intake rocker shafts and exhaust rocker
shafts.

1. Measure diameter of shaft at first rocker location.

MICROMETER

Surface should be smooth.

2. Zero gauge to shaft diameter.

MICROMETER

CYLINDER BORE
GAUGE
Inspect rocker arm

face for wear.

Repeat for all rockers.
3. Measure inside diameter of rocker arm and check for

out-of-round condition.

Rocker Arm-to-Shaft Clearance (IN and EX):
Standard (New):
Primary and Secondary:
0.025-0.052 mm (0.0010-0.0020 in)

Mid:
0.024-0.053 mm (0.0009-0.0021 in)

Service Limit: 0.08 mm (0.003 in)

If over limit, replace rocker shaft and all over-

tolerance rocker arms.
NOTE: If any rocker arm needs replacement, replace
all three rocker arms in that set (primary, mid, and secondary).ProCarManuals.com

Camshafts

Inspection

1. Put the camshafts, the camshaft holders and holder pipes on the cylinder head, and then tighten

the bolts to the specified torque.

NOTE: Apply clean engine oil to 8 mm bolt threads.
Specified torque: 8 mm x 1.25 mm bolts:
22N .
m (2.2 kg-m, 16 Ib-ft)
6 mm x 1.0 mm bolts: 10N .
m (1.0 kg-m, 7 Ib-ft)

CAMSHAFT HOLDER BOLTS TORQUE
SEQNUENCE

FRONT:

REAR:
PLASTIGAGE STRIP
2. Seat the camshaft by pushing it toward left end of
cylinder head.
3. Zero the dial indicator against the left end, then push the camshaft back and forth, and read the end play.Camshaft End Play:
Standard (New): 0.05—0.15 mm

(0.002-0.006
in)

Service Limit: 0.5 mm (0.02 in)
4. Remove the bolts, then remove the camshaft holders from the cylinder head.
Do not rotate the camshaft during inspection.
Remove the rocker arms and rocker shafts.

NOTE:

Lift camshaft out of cylinder head, wipe clean,
then inspect lift ramps. Replace camshaft if lobes
are pitted, scored, or excessively worn. Clean the camshaft bearing surfaces in the
cylinder head, then set camshaft back in place.
Insert plastigage strip across each journal.

5. Install the camshaft holders, and then tighten the

bolts to the specified torque, as shown in the left
column on this page.
6. Remove the camshaft holders and measure widest portion of plastigage on each journal.
Camshaft-to-Holder Oil Clearance:
Standard (New):
0.050-0.089
mm

(0.002-0.004 in)

Service Limit: 0.15 mm (0.006 in)ProCarManuals.com