1998 NISSAN PICK-UP Repair Manual

3. Remove valve oil seals with Tool.
4. Disassemble rocker shaft assembly.
a. Remove rocker shaft lock bolt.
b. Remove valve rocker and rocker shaft bracket.
If it is difficult to remove rocker shaft bracket, immerse
rocker shaft assembly in oil of 70ÉC (158ÉF) for a few min-
utes and then remove bracket.
Inspection
CYLINDER HEAD DISTORTION
Cylinder head distortion: mm (in)
Standard
Less than 0.07 (0.0028)
Limit
0.2 (0.008)
If beyond the specified limit, correct with a surface grinder. Cyl-
inder head height should be greater than 89.7 mm (3.531 in)
after surface has been ground.
VALVE GUIDE CLEARANCE
lValve guide clearance should be measured parallel with
rocker arm. (Generally, a large amount of wear occurs in
this direction.)
Stem to guide clearance: mm (in)
Limit
Intake 0.15 (0.0059)
Exhaust 0.20 (0.0079)
Maximum allowable deflection
(Dial indicator reading)
Intake 0.30 (0.0118)
Exhaust 0.40 (0.0157)
lTo determine the correct replacement part, measure
valve stem diameter and valve guide inner diameter.
Valve stem diameter: mm (in)
Standard
Intake
7.962 - 7.977 (0.3135 - 0.3141)
Exhaust
7.945 - 7.960 (0.3128 - 0.3134)
SEM626BA
SEM627B
SEM648B
SEM586A
EM030
CYLINDER HEADTD
Disassembly (Cont'd)
EM-56

Valve guide inner diameter:
8.000 - 8.015 mm (0.3150 - 0.3156 in)
VALVE GUIDE REPLACEMENT
1. Drive out valve guide with a press [under a 20 kN (2 ton, 2.2
US ton, 2.0 Imp ton) pressure] or hammer, and suitable tool.
2. Press service valve guide onto cylinder head using suitable
tool until the guide projects out 15.8 to 16.2 mm (0.622 to
0.638 in).
3. Ream valve guide.
Finished size:
8.000 - 8.015 mm (0.3150 - 0.3156 in)
VALVE SEATS
Check valve for any evidence of pitting at valve contact surface,
and reseat or replace if worn out excessively.
lWhen repairing valve seats, check valve and valve guide
for wear beforehand. If worn, replace them. Then correct
valve seat.
lThe cutting should be done with both hands for uniform
cutting.
SEM649B
SEM628B
SEM629BA
SEM630B
SEM024-A
CYLINDER HEADTD
Inspection (Cont'd)
EM-57

REPLACING VALVE SEAT FOR SERVICE PARTS
1. Bore out old seat until it collapses or remove valve seats with
Tool.
Place a copper seat between contact surface of Tool and
cylinder head.
2. If the valve seat for the exhaust side is oversized, machine
its mating area (on the cylinder head side) to the dimensions
indicated in the table below. Refer to the figure at the left for
machining procedures.
Unit: mm (in)
Oversized valve
seatBore diameter ``d''
TD25
0.2 (0.008)38.695 - 38.710
(1.5234 - 1.5240)
0.4 (0.016)38.895 - 38.910
(1.5313 - 1.5319)
3. Place new valve seats on dry ice and allow them to cool for
five minutes.
WARNING:
Do not touch cooled valve seats with bare hand.
4. Heat cylinder head to 80ÉC (176ÉF).
5. Install cooled valve seats on cylinder head with Tool.
6. Stake exhaust valve seat at five places with punch.
When staking valve seat, select different places than those
staked before.
SEM631B
DEM031
SEM632B
SEM087
CYLINDER HEADTD
Inspection (Cont'd)
EM-58

7. Cut or grind valve seat using suitable tool at the specified
dimensions as shown in SDS, EM-100.
8. After cutting, lap valve seat with a lapping compound.
9. Check contact condition of valve seat.
COMBUSTION CHAMBER
Check combustion chamber for cracks and other damage. If
necessary, replace.
REPLACING COMBUSTION CHAMBER
Usually combustion chamber should not be removed.
1. Remove combustion chamber so that cylinder head cannot
be damaged.
2. Install combustion chamber.
Identification of combustion chambers
Identification mark
(on combustion chamber)Outer diameter
``D'' mm (in)Engine
3 places 37 (1.46) TD25
(1) Cool combustion chamber with dry ice for approximately 5 to
10 minutes.
WARNING:
Do not touch cooled combustion chamber with bare hand.
(2) Align combustion chamber knock pin with cylinder head
notch, and drive in combustion chamber with a soft hammer.
3. Check amount of protrusion of combustion chamber.
Protrusion:
Standard
þ0.05 to 0.10 mm (þ0.0020 to 0.0039 in)
VALVE DIMENSIONS
Check dimensions in each valve. For dimensions, refer to SDS.
When valve head has been worn down to 0.5 mm (0.020 in)
in margin thickness, replace the valve.
Grinding allowance for valve stem tip is 0.2 mm (0.008 in) or
less.
SEM633B
DEM107
.
SEM634B
SEM188A
CYLINDER HEADTD
Inspection (Cont'd)
EM-59

VALVE SPRING SQUARENESS
Align the valve spring with a square. Rotate the spring to mea-
sure any gap between the top of the spring and the square.
Out-of-square ``S'':
Less than 2.3 mm (0.091 in)
VALVE SPRING PRESSURE LOAD
Refer to SDS, EM-99.
VALVE LIFTER AND PUSH ROD
Valve lifter
1. Check valve lifters for excessive wear on the face.
2. Replace with new ones if worn beyond repair.
a. Valve lifter end should be smooth.
b. Valve lifter to lifter hole clearance: mm (in)
Standard
0.030 - 0.073 (0.0012 - 0.0029)
Limit
Less than 0.20 (0.0079)
Valve lifter outer diameter ``A'':
Standard
25.960 - 25.970 mm (1.0220 - 1.0224 in)
Cylinder block valve lifter hole diameter ``B'':
Standard
26.000 - 26.033 mm (1.0236 - 1.0249 in)
Push rod
1. Inspect push rod for excessive wear on the face.
2. Replace if worn or damaged beyond repair.
3. Check push rod for bend using a dial gauge.
Maximum allowable bend
(Total indicator reading):
Less than 0.5 mm (0.020 in)
SEM635B
EM113
SEM636B
DEM033
CYLINDER HEADTD
Inspection (Cont'd)
EM-60

ROCKER SHAFT AND ROCKER ARM
1. Check valve rockers, brackets and rocker shafts for scoring,
wear or distortion. Replace if necessary.
2. Check clearance between valve rockers and rocker shaft. If
specified clearance is exceeded, replace affected valve rock-
ers or shafts.
Specified clearance: mm (in)
Standard
0.014 - 0.056 (0.0006 - 0.0022)
Limit
Less than 0.15 (0.0059)
Rocker shaft outer diameter ``A'':
Standard
19.979 - 20.000 mm (0.7866 - 0.7874 in)
Rocker arm inner diameter ``B'':
Standard
20.014 - 20.035 mm (0.7880 - 0.7888 in)
3. Check rocker shaft bend at its center. If bend is within speci-
fied limit, straighten it; and if it is greater than specified limit,
replace rocker shaft.
Rocker shaft bend
(Total indicator reading):
Limit
Less than 0.3 mm (0.012 in)
MEASURING CYLINDER HEAD TO VALVE DISTANCE
Measure distance from cylinder head surface to intake and
exhaust valves. If specified distance is exceeded, replace
valve(s) or valve seat(s).
Specified distance: mm (in)
Standard
Intake and Exhaust
0.7 - 1.3 (0.028 - 0.051)
Limit
Less than 1.7 (0.067)
for intake and exhaust valves
SEM027
SEM028
SEM026.SEM026
CYLINDER HEADTD
Inspection (Cont'd)
EM-61

Assembly
1. Assemble rocker shaft component parts.
lFace punch mark toward the front of the engine.
Identification of rocker arms
Identification mark
(At area
Vaon rocker arm)For use with
Two ridges Intake
No ridge Exhaust
2. Install valve component parts.
Identification of valves
Identification mark
(on intake and exhaust valve)
Engine
Intake valve Exhaust valve
2 B TD25
lAlways use new valve oil seal. (Refer to EM-68.)
lInstall valve spring (uneven pitch type) with its narrow
pitch side toward cylinder head side.
DEM034
SEM066C
MEM180A
SEM615F
SEM638B
CYLINDER HEADTD
EM-62

Installation
1. Install cylinder head gasket.
Identification of cylinder head gaskets
Identification cut hole
(on cylinder head gas-
ket)Inner diameter
``d'' mm (in)Engine
2 94.4 (3.717) TD25
a. When replacing only cylinder head gasket, install same
grade gasket as the one formerly used.
b. When replacing or repairing cylinder block, cylinder head,
piston, connecting rod and crankshaft, select gasket as fol-
lows:
lSelecting gasket thickness
(1) Measure piston projection from cylinder block surface.
a. Measure the projection a and a¢(cylinder liner height above
cylinder block) at two points in each cylinder.
b. Measure the projection b and b¢(piston height above cylin-
der block) at two points, when the piston is at the top dead
center position.
c. Calculate the piston height projection above cylinder liner b
-a(b¢-a¢).
d. Average the two projections (piston height above cylinder
liner) for each cylinder H
L.
(2) Select suitable cylinder head gasket which conforms to the
largest amount of projection of the four pistons.
Unit: mm (in)
Average values piston projections HL
Gasket thicknessGasket
grade num-
ber New parts In assembly
Less than 0.168 (0.0066)1.35
(0.0531)1.20
(0.0472)2
0.168 - 0.218 (0.0066 - 0.0086)1.40
(0.0551)1.25
(0.0492)3
More than 0.218 (0.0086)1.45
(0.0571)1.30
(0.0512)4
Make sure that No. 1 piston is at TDC on its compression
stroke.
SEM250F
.
DEM036
MEM079A
CYLINDER HEADTD
EM-63