Isuzu N-Series. Service manual - part 583

6A1-20 4JB1/4JB1-TC/4JG2/4JH1-TC - ENGINE

Caution:
Put removed valve spring in the order of cylinder num-
ber.

4. Valve Guide Oil Seal

• Remove valve guide oil seal by pliers

Caution:
Removed oil controller should not be reused.

Installation

1. Valve Guide Oil Seal

• Install new valve guide oil seal in valve.
• Guide using special tool.

Special tool: 5-8840-2033-0

2. Valve Spring

• Attach the new valve spring to the upper spring

seat.

Caution:

• The painted area of the valve spring should be fac-

ing toward.

• Apply compressed air to cylinder from the glow

plug hole to hold the valve in place.

• Install split collar by special tool

Valve spring compressor: 9-8523-1423-0 (J-
29760)

3. Rocker Arm Shaft Assembly

• Install rocker arm shaft with larger oil hole 

φ4) to

the front of engine.

• Align fixing bolt with nut of rocker arm shaft and

tighten fixing bolts to the specified torque.

Tighten:

• 54  N

⋅m (5.5 kg⋅m / 40 lb⋅ft)

• Valve clearance adjustment

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4JB1/4JB1-TC/4JG2/4JH1-TC - ENGINE 6A1-21

4. Valve clearance adjustment

Above works refer to “ROCKER ARM SHAFT AS-
SEMBLY” Section in this manual.

5. Cylinder Head Cover

• Apply engine oil to the rocker arms and the valve

spring.

• Install the cylinder head cover gasket to the cylin-

der head cover.
The gasket must be perfectly smooth with no loose
areas.

• Install cylinder head cover and tighten bolt to the

specified torque.

Tighten:

• Head cover bolt to 13 N

⋅m (1.3 kg⋅m / 113 lb⋅in)

• Connected PCV hose.
• Connect battery ground cable.

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6A1-22 4JB1/4JB1-TC/4JG2/4JH1-TC - ENGINE

TIMING GEAR (4JB1, 4JB1-TC, 4JH1-TC Gear Type)

Component

Removal

Preparation

• Disconnect battery ground cable.
• Drain coolant.

1. Fan Shroud

2. Power Steering Pump Drive Belt (P/S Model)

• Loosen power steering pump mounting bolt and

adjust bolt, and remove the drive belt.

3. AC Generator Drive Belt

Legend

1. Fan shroud

9. Oil pipe

2. Power steering pump drive belt

10. Idle gear

3. AC generator drive belt

11. Idle gear “B”

4. Cooling fan assembly

12. Idle gear

5. Crankshaft damper pulley

13. Injection pump

6. Noise shield cover

14. Camshaft timing gear

7. Noise cover spacer

15. Crankshaft gear

8. Timing gear case cover

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4JB1/4JB1-TC/4JG2/4JH1-TC - ENGINE 6A1-23

• Loosen AC Generator mounting bolt (under size)

and adjust plate lock bolt, and remove the drive
belt.

4. Cooling Fan Assembly

• Remove clamp nut, and remove cooling fan as-

sembly, distant pipe, and fan pulley.

5. Crankshaft Damper Pulley
6. Noise Shield Cover
7. Noise Cover Spacer
8. Timing Gear Case Cover
9. Oil Pipe

10. Idler Gear

1) Measure the camshaft timing gear backlash

and the crankshaft timing gear backlash before
removing the idler gear.

2) Measure the idler gear end play before remov-

ing the idler gear.

Notice:
Refer to the following items for details on the backlash
and end play measurement procedures.

11. Timing Gear Backlash Measurement

1) Set a dial indicator to the timing gear to mea-

sured.
Hold both the gear to be checked and the ad-
joining gear stationary.

2) Move the gear to be checked as far as possible

to both the right and the left.
Take the dial indicator reading.
If the measured value exceeds the specified
limit, the timing gear must be replaced.

12. Idler Gear “A” End Play Measurement

Insert a feeler gauge between the idler gear and
the thrust collar to measure the gap and determine
the idler gear end play.
If the measured value exceeds the specified limit,
the thrust collar must be replaced.

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Timing Gear Backlash

mm (in)

Standard

Limit

0.010 — 0.17 (0.0039 — 

0.0067)

0.30 (0.012)

Idle Gear End Play

mm (in)

Standard

Limit

0.07 (0.0028)

0.2 (0.0079)

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