Isuzu N-Series. 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.
N6A3254E
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)
N6A3257E
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