Isuzu engine 4j series. Manual - part 28

 

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Isuzu engine 4j series. Manual - part 28

 

 

6A – 48

  GENERAL ENGINE MECHANICAL

7. Piston Ring

Remove the piston rings with a piston ring expander.
Arrange the removed piston rings in the cylinder number
order.

8. Piston Pin Snap Ring

•

Use a pair of pliers to remove the piston pin snap
rings.

9. Piston Pin

NOTE:

Keep the parts removed from each cylinder separate.
All parts must be reinstalled in their original positions.

10. Piston

11. Connecting Rod

INSPECTION AND REPAIR

PISTON AND PISTON RING

Pistons

Carefully clean away all the carbon adhering to the piston
head and the piston ring grooves.

NOTE:
Never use a wire brush to clean the pistons. Damage will
result.
Visually check each piston for cracking, scoring, and other
signs of excessive wear.
If any of the above conditions are present, the piston must
be replaced.

Piston Diameter

1. Measure the piston outside diameter with micrometer

at the piston grading position.

Piston Grading Position

mm (in)

4JB1 / 4JB1T / 4JB1TC

74 (2.913)

4JG2

71.00 (2.797)

6A-48-2.tif

6A-48-3.tif

6A-48-1.tif

GENERAL ENGINE MECHANICAL   6A – 49

4JB1 / 4JB1T / 4JB1TC

mm (in)

Size Mark

Outside Diameter

A

92.985 - 92.994 (3.6608 - 3.6612)

B

92.995 - 93.004 (3.6612 - 3.6616)

C

93.005 - 93.014 (3.6616 - 3.6620)

D

93.015 - 93.024 (3.6620 - 3.6624)

4JG2

mm (in)

Size Mark

Outside Diameter

A

95.365 - 95.374 (3.7545 - 3.7549)

B

95.375 - 95.384 (3.7549 - 3.7553)

C

95.385 - 95.394 (3.7553 - 3.7557)

D

95.395 - 95.404 (3.7557 - 3.7561)

The grading position for piston outside diameter is
represented by the ‘G’ as shown in Figure.
Measure the cylinder bore inside diameter (refer to
“inspection of the cylinder Block” in this Section).
If the piston clearance does not conform to the specified
valve, the piston and/or cylinder liners must be replaced.
Piston Clearance

mm (in)

4JB1 / 4JB1T / 4JB1TC

0.061 (0.0024)

4JG2

0.066 (0.0026)

Selection method of piston grade for service parts.

If you find piston grade A from size mark or piston outside
diameter measurement result, you will select AX for
service piston grade.
The stamped piston grade on the head of piston for
service parts.
Service piston grade

Piston Size Mark

Service Parts Grade

A

AX

B

AX

C

CX

D

CX

Service piston diameter

mm (in)

Piston Grade

4JB1 / 4JB1T / 4JB1TC

AX

92.989 - 93.004 (3.6610 - 3.6616)

CX

93.005 - 93.020 (3.6616 - 3.6622)

Piston Grade

4JG2

AX

95.369 - 95.384 (3.7547 - 3.7553)

CX

95.385 - 95.400 (3.7553 - 3.7559)

6A-49-1.tif

6A – 50

  GENERAL ENGINE MECHANICAL

NOTE:

It is most important that the correct piston grade be
used. Failure to select the correct piston grade will
result in engine failure. Always measure the cylinder
bore and select the correct piston grade.

Piston rings

Any worn or damaged part discovered during engine
overhaul must be replaced with a new one.
1. Ring end gap measurement
•

Insert the piston ring into the bore.

•

Push the ring by the piston, at a right angle to the wall,
into the point ring at which the cylinder bore diameter
is the smallest.

•

The top mark of the piston ring are shown in the
illustration.

4JB1 / 4JB1T / 4JB1TC

mm.(in)

Standard

Limit

1st

0.20 - 0.40

(0.0079 - 0.0157)

Compression
ring

2nd

0.20 - 0.40

(0.0079- 0.0157)

Oil ring

0.10 - 0.30

(0.0039 - 0.0118)

1.5

(0.059)

4JG2

mm.(in)

Standard

Limit

1st

0.20 - 0.35

(0.0079 - 0.0138)

Compression
ring

2nd

0.37 - 0.52

(0.0146 - 0.0205)

Oil ring

0.20 - 0.40

(0.0079 - 0.0157)

1.5

(0.059)

2. Measure the clearance between the piston ring groove

and the piston ring with a feeler gauge. If the piston
ring groove/piston ring clearance exceeds the
specified limit, the piston must be replaced.

4JB1 / 4JB1T / 4JB1TC

mm (in)

Standard

Limit

1st

0.090 - 0.125

(0.0035 - 0.0049)

Compression
ring

2nd

0.050 - 0.075

(0.0020 - 0.0030)

Oil ring

0.03 - 0.07

(0.0012 - 0.0028)

0.15

(0.0059)

6A-50-1.tif

6A-50-2.tif

6A-50-3.tif

GENERAL ENGINE MECHANICAL   6A – 51

4JG2

mm (in)

Standard

Limit

1st

0.09-0.13

(0.0035 - 0.0051)

Compression
ring

2nd

0.05 - 0.07

(0.0020 - 0.0028)

Oil ring

0.03-0.07

(0.0012-0.0028)

0.15

(0.0059)

Piston pin

Visually inspect the piston pin for cracks, flaws, and other
damage and replace if necessary.
1. Use a micrometer to measure the piston pin outside

diameter in both directions at three different positions.
If the measurement exceed the specified limit the
piston pin must be replaced.

Piston pin outside diameter

mm (in)

Standard

Limit

4JB1 /

4JB1T

4JB1TC

30.995 - 31.000

(1.2202 - 1.2204)

30.970 (1.2190)

4JG2

33.995 - 34.000

(1.3384 - 1.3386)

33.970 (1.3374)

2. Measure the inside diameter of the connecting rod

small end. If the clearance between the small end and
pin does not conform to the specified value, the
connecting rod or bushing and pin must be replaced.

mm (in)

Standard

Limit

Clearance

0.008 - 0.020

(0.0003 - 0.0008)

0.05

(0.0020)

3. Insert the piston pin into the piston and rotate it. If the

pin rotates smoothly with no backlash, the clearance is
normal. If there is backlash or roughness, measure the
clearance. If the clearance exceeds the specified limit,
the piston and the piston pin must be replaced.

mm (in)

Standard

Limit

Clearance

0.002 - 0.004

(0.00008 - 0.00016)

0.04

(0.0016)

6A-51-1.tif

6A-51-2.tif

 

 

 

 

 

 

 

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