Isuzu N-Series. Service manual — part 317

6A-10 ENGINE MECHANICAL

Valve Spring Squareness

Use a surface plate and a square to measure the valve
spring squareness.
If the measured value exceeds the specified limit, the
valve spring must be replaced.

Valve Spring Tension

Use spring tester to measure the valve spring tension.
If the measured valve is less than the specified limit, the
valve spring must be replaced.

Valve Guide

Caution:
Taking care not to damage the valve seat contact sur-
face, when removing carbon adhering to the valve head.
Carefully inspect the valve stem for scratching or abnor-
mal wear. If these conditions are present, the valve and
the valve guide must be replaced as a set.

Valve Stem and Valve Guide Clearance

(Measuring Method-I)

1. Set the dial indicator to the valve stem measuring

point.

2. Move the valve stem end from side to side.

Read the dial indicator.
Note the total indicator reading.
If the measured values exceed the specified limit,
the valve and the valve guide must be replaced as
a set.

Valve Spring Squareness

mm (in)

Limit

1.0 (0.04)

Valve Spring Tension

N (kg/lb)

Set Length

mm (in)

Standard

Limit

47.0 (1.85)

414 — 477 (42.2 —

48.6/93 — 107)

401 (40.9/98)

N6A0120E

N6A0121E

Total Dial Indicator Reading
(Valve Stem and Valve Guide
Clearance)

mm (in)

Valve

Standard

Limit

Intake Valve

0.038 — 0.071

(0.0015 —

0.0028)

0.20 (0.0079)

Exhaust Valve

0.064 — 0.096

(0.0025 —

0.0038)

0.25 (0.0098)

N6A0122E

ENGINE MECHANICAL 6A-11

(Measuring Method-II)

1. Measure the valve stem outside diameter.

Refer to the “Valve Stem Outside Diameter”.

2. Use a caliper calibrator or a telescoping gauge to

measure the valve guide inside diameter.

3. Calculate the clearance between the valve guide

inside diameter and the valve stem outside diame-
ter.
If the clearance exceeds the specified limit, the
valve and the valve guide must be replaced as a
set.

Valve Stem Outside Diameter

Measure the valve stem diameter at three points.
If the measured valve is less than the specified limit, the
valve and the valve guide must be replaced as a set.

Valve Guide Replacement

Valve Guide Removal
Use a hammer and the valve guide replacer to drive out
the valve guide from the cylinder head lower face.
Valve Guide Replacer: 5-8840-2227-0

Valve Guide Installation

1. Apply engine oil to the valve guide outer circumfer-

ence.

2. Attach the valve guide installer to the valve guide.

Valve Guide Replacer: 5-8840-2227-0

N6A0123E

N6A0124E

Valve Stem Outside Diameter

mm (in)

Valve

Standard

Limit

Intake Valve

8.946 — 8.962

(0.3522 —

0.3528)

8.88 (0.350)

Exhaust Valve

8.921 — 8.936

(0.3512 —

0.3529)

8.80 (0.346)

N6A0125E

N6A0126E

6A-12 ENGINE MECHANICAL

3. Use a hammer to drive the valve guide into position

from the cylinder head upper face.

4. Measure the height (H) of the valve guide upper

end from the cylinder head upper face.

Notice:
If the valve guide has been removed, both the valve and
the valve guide must be replaced as a set.

Valve and Valve Seat Insert

Valve Thickness and Depression

1. Measure the valve thickness.

If the measured value is less than the specified lim-
it, the valve and the valve seat insert must be re-
placed as a set.

2. Install the new valve (1) to the cylinder head (2).

3. Use a depth gauge or a straight edge with steel

rule to measure the valve depression from the cyl-
inder head lower surface.
If the measured value exceeds the specified limit,
the valve seat insert and/or the valve must be re-
placed.

Valve Guide Upper End Height (H)

mm (in)

14.1

± 0.2 (0.555 ± 0.008)

N6A0127E

N6A0128E

Intake and Exhaust Valve Thickness

mm (in)

Valve

Nominal Size

Limit

Inlet

1.8 (0.071)

1.3 (0.051)

Exhaust

1.75 (0.069)

1.3 (0.051)

Intake and Exhaust
Valve Depression

mm (in)

Standard

Limit

0.7 — 1.2 (0.028 —

0.047)

2.5(0.098)

N6A0129E

N6A0130E

ENGINE MECHANICAL 6A-13

Valve Contact Width

1. Check the valve contact faces for roughness and

unevenness.
Make smooth the valve contact surfaces.

2. Measure the valve contact width.

If the measured value exceeds the specified limit,
the valve seat insert must be corrected or replaced.

Contact Surface Angle on Valve Seat on Valve

1. Measure contact surface angle on valve seat.
2. If the measured value exceeds the limit, replace

valve, valve guide and valve seat as a set.

Valve Seat Insert Replacement

Valve Seat Insert Removal

1. Arc weld the entire inside circumference (1) of the

valve seat insert (2).

2. Allow the valve seat insert to cool for a few min-

utes. This will invite contraction and make removal
of the valve seat insert easier.

3. Use a screwdriver (3) to pry the valve seat insert

free. Take care not to damage the cylinder head
(4).

4. Carefully remove carbon and other foreign material

from the cylinder head insert bore.

Valve Seat Insert Installation

1. Carefully place the attachment (1) (having a small-

er outside diameter than the valve seat insert) on
the valve seat insert (2).

Notice:
The smooth side of the attachment must contact the
valve seat insert.

Valve Contact Width

mm (in)

Valve

Nominal Size

Limit

Intake

2.5 (0.098)

3.0 (0.118)

Exhaust

2.0 (0.079)

2.5 (0.098)

Standard

Degrees

45

°

N6A0131E

N6A0132E

N6A0133E