1990 MITSUBISHI ECLIPSE Service Manual

9-12
CRANKSHAFT PULLEY
ENGINE- Base EngineDrives the water
pump and alternator
Hub-
Pulley -Drives the air
conditioner
compressor
Fin
Rubber
6EMI2526EN0145 Timing belt cover
(1) The crankshaft pulley not only drives the water
pump and alternator, but also functions as a
torsional damper to reduce torsional vibration of
the crankshaft.
SILENT SHAFT SYSTEM(2) There are fins provided at the back of the pulley
that ventilate the inside of the timing belt cover:
when the pulley rotates, they draw air out of the._
timing belt cover.
Forward
@
/I
Center of crankshaftSilent shaft --
6ENl32The silent shaft system counteracts the secondaryreducing the vibration and noise generated by the
exciting moment in the engine’s vertical direction asengine. The system is exactly the same as that used
t uluv -well as the rolling moment, thereby drastically
in the conventional 4G63-SOHC engine.
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ENGINE - Base Engine9-13
VALVE MECHANISM
!
Rocker arm
Exhaustcamshaf
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Exhaust valve
bENOIntake valve6ENOlOOIft
(1) The valve mechanism is the DOHC 16-valvesystem.
.(2) The rocker arm with a roller follower. i.e., the
roller rocker arm, is used that reduces drastically
the friction loss of the valve train.
(3) The hydraulic type lash adjusters automatically
adjust the valve clearance, minimizing noisegenerated by the valve train. They also eliminate
the need for valve clearance adjustment.
(4) The valve springs, whose cross section is oval.contribute to the enhanced spring load. This in
turn ensures that the valves operate properly.
especially at high speed.
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ENGINE - Base Engine
ROCKER ARM
(1) The cam follower of the rocker arm is a roller with nea,.,-
bearings.
v
,I$- I- ‘Roller
Needle bearing6ENOlOI
6EN025-4
2-valve SOHC slipper type
9O-valve DOHC roller type1
02.5005.000Engine speed
rpm6ENOl o(Camshaft
I-Oil passage ,
EIr(2) A jet of oil spurts onto the contact area between the cam
and roller from an oil jet located on the fulcrum side of the
rocker arm.
(3) Since the roller rotates as the cam rotates, friction loss is
drastically reduced as compared with the conventional
slipper type.
(4) Due to the construction of the roller rocker arm, the valve
train driving torque is reduced to about half that of the
conventional slipper type, which is equivalent to, or
compares favorably with, the
2-valve SOHC slipper type. All
these factors contribute to enhanced engine performa
and fuel economy.
LASH ADJUSTER
,The hydraulic lash adjuster is of the end pivot type. It eliminates
the need for adjustment of the valve clearance. There are four
lash adjusters provided for each cylinder, 16 in all.
Rocker anIF=Lash adjuster
-
Cylinder head
--Valve
‘-Reservoir chamber
6E NO255
-6EN0256

5-jENGINE- Base Engine9-15Operation of the Lash Adjuster
When the valve starts opening
/f-b
During the valve opening stroke
n
6EN0254
When the valve coiqpletesthe opening stroke
6EN0257
6EN0256
(1) Before the valve starts opening:
--
No external load is applied to the
plunger, thus
causing the plunger to be pushed UP
by theplunger spring, maintaining zero clearance.
.(2) When the valve starts opening:
When the cam pushes the rocker arm, the ball inthe high-pressure chamber immediately is held
pressed against the seat by the hydraulic press-
ure. fully closing the high-pressure chamber. AS
the check ball closes, the pressure in the
high-pressure chamber surges causing the plun-ger to support the load from rocker arm, which
.allows the valve to start ooenino.
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(3) During the valve opening stroke:
A very small amount of oil leaks through the
clearance between the lash adjuster body and
plunger.
(4) When the valve completes its opening stroke:
There is no external load being applied to the
plunger as the valve closes, causing the plunger
to be pushed up by the plunger spring. This
causes the pressure in the high-pressure cham-
ber to be lowered, which pushes the check ball
open. The oil which has leaked is replaced in thehigh-pressure chamber from the reservoir cham-
ber.
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9-16ENGINE- Base Engine
Hydraulic Flow to Lash Adjusters
To lash adjuster onthe exhaust side
P
)
5-Valve body
.Lash adjuster
6EN0107
:.-.
2:.
4
‘.’Relief plunger
I?.,:.:.;
/Lash adjuster
-Cylinder head bolt hole
PlugTo
tash adjuster onthe intake side
Relief spring
-Valve body
6EN0108The oil moves through the cylinder head bolt hoie to
the oil passages drilled in the cylinder head. Andthen has its pressure regulated by the valve body k
pressure regulator) and is supplied to each
la:
adjuster.
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ENGINE- Base Engine9-17CAMSHAR
Exhaust camshaftStamped identification mark
-
-
k--JL---J
No. 1 camsNo. 2 camsNo. 3 cams
No. 4 camsIntake camshaftIt’ II’ II1
NOTEJ = Journal
Crank angle sensor6EN0112
(1) Each camshaft is supported by the six bearings.(2) A hexagon between the No. 1 and No. 2 cams is
provided for holding the camshaft with a wrench
when loosening or tightening the
catishaftsprocket bolt.
TIMING BELT TRAIN
Exhmmt rid.Intake tide
Camshatt sprookec(No. of teeth: 461Camshaft sprocket(No. of teeth: 461
MN0139
6tNOl10
011 Pump stmoket(No. o! teeth: 18)
Crankshatr spmokst(No. of loath: 2416EN0114

9-18ENGINE- Base Engine
(1) The intake camshaft, exhaust camshaft, and the
oil pump are driven by a single timing belt.
(2) Timing belt tension varies at different engine
temperatures and ages of the belt. The autotensioner absorbs these changes in belt
ten+n,not only to prevent the noise problem
getting worse, but to improve durability as weli’l
AUTO TENSIONER
Piston -1
Check ball-4,
SpringTensioner
cwllev
6EN0116
LOoil seal
6ENOWThe auto tensioner applies tension to the timing belt
by causing the tensioner arm to move back and
forth in the directions shown by arrow
@I.The bottom figure shows the construction of the
aUt0 tensioner. The chambers on the right and leftof the piston
are filled with silicone oil.
Both the tensioner pulley and idler pulley are of the
ball bearing type into which grease has been
packed.

,_-.._-~_._. I _ ‘... ----
ENGINE- Base Engine9-19
Reservoir
chamber/
Reservoir
chamber
PressurechamberOperation of the Auto Tensioner
WHEN THE BELT TENSION HAS INCREASED
(1) The tensioner arm pushes the piston in the direction shown
by
arrow @, causing the hydraulic pressure in the pressurechamber to build up.
(2) The check ball closes.
(3) The oil inthepressure chamber is compressed by the
piston, which causes a small amount of oil to gradually leak
through the clearance between the piston and cylinder into
the reservoir chamber. This causes the piston to move
slowly in the direction shown by arrow
@.
(4) The piston stops moving when the load in the direction @balances the spring tension, which determines the load,
i.e., tension, applied to the belt.
WHEN THE BELT TENSION HAS DECREASED
(1) The piston moves in the direction shown by arrow @I by the
spring tension.
(2) As the piston moves, the hydraulic pressure in the pressure
chamber becomes lower than that in the reservoir cham-
ber.
(3) The check ball opens.
(41 Oil enters the pressure chamber.
(5) The piston stops moving when the belt tension balances
the spring tension, which determines the tension applied to
the belt.
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