Isuzu N-Series. Manual - part 338

6A3-4 ENGINE (4HF1 / 4HF1-2 / 4HE1-TC / 4HG1 / 4HG1-T)

For 4HG1-T

For 4HE1-TC (4HE1-XS) 98EPA

For 4HE1-TC (4HE1-XS) 98EPA

For 4HE1-TC (4HE1-XS) SPEC. EURO3

N6A0362E

N6A0363E

N6A0364E

N6A0365E

ENGINE (4HF1 / 4HF1-2 / 4HE1-TC / 4HG1 / 4HG1-T) 6A3-5

For 4HE1-TC (4HE1-XS) SPEC. EURO3

For 4HE1-TC (4HE1-XS) SPEC. EURO3

Cylinder Head

• The cylinder head is made of cast iron and has a

crossflow layout with the intake system in the left
side and the exhaust system in the right side, de-
signed to reduce resistance in the intake and ex-
haust systems.

• The valve diameter is increased to offset the mass

of the valve operating system reduced by the intro-
duction of the OHC mechanism.
In addition, the intake and exhaust ports are put in
a smoother and less resistant layout to enhance in-
take and exhaust efficiency.

• The cylinder head gasket is of the laminated steel

of least fatigue in combination with the angular cyl-
inder head bolt tightening method, equally de-
signed to increase reliability against gas and water
leakage, in addition, selective assembly of gaskets
of various thicknesses minimizes the wasted

space between the piston and the cylinder head to
maintain performance at a high level.

• The cylinder head cover is made of aluminum to re-

duce noise.

Cylinder Block

• The cylinder block (1) is made of cast iron having

dry cylinder liner and five bearings.
The bearing cap has a ladder frame (2) construc-
tion integrating the crankcase to increase rigidity.

• The cylinder liner is made of thin iron plus special

alloys and is combined with the chrome-plated pis-
ton ring to ensure good resistance against wear.

• The oil pan is made of vibration-damping steel to

reduce noise.

N6A0366E

N6A0367E

N6A0368E

6A3-6 ENGINE (4HF1 / 4HF1-2 / 4HE1-TC / 4HG1 / 4HG1-T)

Piston, Connecting Rod and Crankshaft

• The piston is made of aluminum alloy. A ring trigger

is cast into the top ring groove and chrome plating
is applied to four sides of the top ring to ensure suf-
ficient strength and wear resistance of the ring and
the ring groove. The piston bottom has a thermal
flow shape to increase cooling efficiency of the oil-
ing jet. This design reduces thermal load while in-
creasing rigidity (see figure).

• The combustion chamber has a square shelf of

proven performance to ensure outstanding stability
in exhaust gas control (see figure).

• The autothermatic piston and offset piston pin re-

duces piston flapping and other noise.

• The crankshaft is made of cast carbon steel with

five bearings and eight counterweights to reduce
revolution load to the bearing. The ladder frame
design that integrates the bearing cap and the
crankcase increases bearing rigidity. The angular
tightening method of the bearing bolt further in-
creases reliability and durability.

N6A0369E

Legend

1. Ring trigger
2. Strut

Legend

1. Chrome plated
2. Top ring
3. 2nd ring
4. Nitriding
5. Oil ring expander

N6A0370E

N6A0371E

ENGINE (4HF1 / 4HF1-2 / 4HE1-TC / 4HG1 / 4HG1-T) 6A3-7

• The connecting rod is made of cast carbon steel

and the cap is bolted by angular tightening method
to maintain reliability.

• The bearing, as well as the crank journal and crank

pin bearings, are made of Kelmet metal.
Oil clearance is controlled accurately through se-
lective assembly by thickness to reduce noise and
increase reliability.

• The crankshaft has the axial type oil seal that dras-

tically improves durability and reliability.
Compared with the conventional radial type (lips in
a radial orientation), the axial type oil seal has lips
in an axial orientation to minimize lip wear. It also
precludes lip peeling and damage, spring disloca-
tion and other problems associated with the radial
type oil seal (see figure).

Valve Train

• The gear train is located at the end of the cylinder

block to minimize influence of the torsional vibra-
tion of the crankshaft and the radiant sound. Noise
is further reduced, to the same level as a timing
belt driven system, by integrating the crank gear
with the crankshaft by shrink fit and by careful turn-
ing of the gear precision, teeth contact ratio of
gear, backlash, bearing rigidity, neutral frequency,
etc. (See figure).

• Gears are of the forged type. Gears are tufftrided

to secure sufficient durability.

• The camshaft is made of carbon steel with five

bearings. The cam’s nose and the journal are in-
duction-hardened to secure sufficient durability.

• The cam has a Fourier-dyne profile to maximize

the intake and exhaust valve lifts and the valve
opening and closing timing is optimized to increase
intake and exhaust efficiency.

• The valve spring is a single spring having an egg-

shaped cross section to reduce weight while reduc-
ing stress. Coupled with the unique cam profile, the
spring increases the jump-and bounce-free limit at
high-speed operation to provide reserve character-
istics.

• The rocker arm is made of diecast aluminum and is

of the center pivot type having a roller. This in-
creases reliability while reducing friction and con-

Legend

A. Crankshaft oil seal

1. Axial type
2. Radial type
3. Slinger

N6A1629E

Legend

1. Camshaft gear
2. Power steering pump gear
3. Power steering pump idle gear
4. Crankshaft gear
5. Oil pump drive gear
6. Injection pump gear
7. Idle gear A
8. Idle gear B
9. Idle gear C

N6A0373E