OverviewsA Service Bulletin/Repair Instructions

Variable Camshaft Timing Operation
‘SYSTEM OVERVIEWS
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3

4
24-Vaive VRE @

Variable Camshaft Timing Operation
24-Valve VRE @

Timing Setup Variable Camshaft Timing Operation
Operation Q

SVSTEM OVERVIEWS
Variable Valve Timing for the 24-valve

VR6 was developed to open and close

valves at precise points during the

combustion process.
Camshafts with fixed timing are designed

to provide a compromise power due to

fixed valve opening and closing.

Adjustable camshaft timing systems can

provide more power and economical

operation, while still meeting stringent

emissions requirements.
The adjustable camshaft system in _Intake Camshaft Adjuster

the 24-valve VR6 engine is

comprised of:
+ An Intake Camshaft Adjuster
‘The adjustable camshaft system in _‘Intake Camshaft Adjuster

the 24-valve VR6 engine is

comprised of:
+ An Intake Camshaft Adjuster

+ An Exhaust Camshaft Adjuster
Exhaust Camshaft Adjuster
The adjustable camshaft system in _Intake Camshaft Adjuster

the 24-valve VR6 engine is

comprised of:
+ An Intake Camshaft Adjuster
+ An Exhaust Camshaft Adjuster
+ Valve for Camshaft Adjustment

(Intake) N205
Exhaust Camshaft Adjuster

Valve for Camshaft Adjustment

(Intake) N205
@ wv
The adjustable camshaft system in _Intake Camshaft Adjuster

the 24-valve VR6 engine is

comprised of:
+ An Intake Camshaft Adjuster
+ An Exhaust Camshaft Adjuster
+ Valve for Camshaft Adjustment

(Intake) N205
+ Valve for Camshaft Adjustment

(Exhaust) N318
Exhaust Camshaft Adjuster

Valve for Camshaft Adjustment

(Intake) N205
Valve for Camshaft Adjustment

(Exhaust) N318
The adjustable camshaft system in _Intake Camshaft Adjuster

the 24-valve VR6 engine is

comprised of:
Timing Chain
+ An Intake Camshaft Adjuster
+ An Exhaust Camshaft Adjuster
+ Valve for Camshaft Adjustment

(Intake) N205
+ Valve for Camshaft Adjustment

(Exhaust) N318
+ Timing Chain
Exhaust Camshaft Adjuster

Valve for Camshaft Adjustment

(Intake) N205
Valve for Camshaft Adjustment

(Exhaust) N318
The adjustable camshaft system in _Intake Camshaft Adjuster

the 24-valve VR6 engine is

comprised of:
Timing Chain
+ An Intake Camshaft Adjuster
+ An Exhaust Camshaft Adjuster
+ Valve for Camshaft Adjustment

(Intake) N205
+ Valve for Camshaft Adjustment

(Exhaust) N318
+ Timing Chain
+ Motronic Engine Control Module

(ECM) - not shown
Exhaust Camshaft Adjuster

Valve for Camshaft Adjustment

(Intake) N205
Valve for Camshaft Adjustment

(Exhaust) N318
Each Camshaft Adjuster is

composed of:
+ Sprocket
eo
Each Camshaft Adjuster is Base Cylinder

composed of:
+ Sprocket (connected to the cover)

+ Base Cylinder (connected to the

cover)
Each Camshaft Adjuster is Base Cylinder

composed of:
+ Sprocket (connected to the cover)
+ Base Cylinder (connected to the

cover)
+ Rotor (connected to the

camshaft)
Rotor
Each Camshaft Adjuster is Base Cylinder

composed of:
+ Sprocket (connected to the cover)
+ Base Cylinder (connected to the

cover)
+ Rotor (connected to the

camshaft)
+ Cover
Rotor
Each Camshaft Adjuster is Base Cylinder

composed of:
+ Sprocket (connected to the cover)
+ Base Cylinder (connected to the

cover)
+ Rotor (connected to the

camshaft)
+ Cover
+ Camshaft Position Sensor Reluctor
Camshaft Position

Sensor Reluctor Rotor
A)
As the chain drives the cover, the base

cylinder is turned. This, in turn, pushes

‘on the rotor, turning the camshaft.
@ w
Advance oil pressure Retard oil pressure

The space between the rotor and base
cylinder is filled with oil. The Valves for

Camshaft Adjustment can direct oil

pressure to either side of the rotor,

controlling the separation of the rotor

from the base cylinder. This causes the

camshaft to rotate to a different position,

changing the timing of the valves.
a Outer section driven

This piece rotates when by timing chain

pressure is applied, and is
directly connected to the
camshaft.
A)
The camshaft adjusters have different

internal chamber widths. As a result,

the intake camshaft can rotate up to

25 degrees in either direction from its

original position. The intake camshaft

is infinitely adjustable within this range.
The exhaust can rotate 11 degrees in

either direction and is always either

fully advanced or fully retarded.
Valves for Camshaft Adjustment:
The oil pressure responsible for rotating

the camshafts is delivered by the Valves

for Camshaft Adjustment. This oil runs

through passages and into either the "A"

or “B™ chamber of the Camshaft Adjuster

assembly. If oil is run to the "A" chamber,

the rotor will remain in its resting state.
If oil is run to the “B™ chamber, the rotor

will move to advance the opening and

closing of the valves.
@ ®
Variable Camshaft Operation-

Idling:
“A" chamber “B" chamber
Intake Camshaft - Oil pressure to "A"

chamber, rotor at its resting state, valves

open at 25 degrees after Top Dead

Center.
Exhaust Camshaft - Oil pressure to "B"

chamber, rotor advanced 22 degrees,

closing 25 degrees before Top Dead

Center.
@ w
Variable Camshaft Operation-

Working positions - above 1200 rpm

and under load: “B" chamber "A" chamber
Intake Camshaft - Oil pressure to "B"

chamber, rotor advanced 25 degrees

after and 25 degrees before Top Dead

Center.
Exhaust Camshaft - Oil pressure to "A"

chamber, rotor returns to its resting state,

exhaust valves will close 3 degrees

before Top Dead Center
¥ Module complete

© Click to Replay Overview
Cams @

Camshaft Timing Operation
Timing Setup
SYSTEM OVERVIEWS
&

Timing Setup
When servicing the 24-valve VR6,

there is a specific procedure used

to reset the timing.
@
Timing Setup
First, turn the crankshaft until the mark

on the damper aligns with the mark on

the engine block. This assures that the

engine is at Top Dead Center.
@ w
Timing Setup
To make sure that the engine is at the

correct Top Dead Center position, look

for a slot on the top of the intermediate

shaft sprocket.
This slot can only be seen every

second Top Dead Center position.
@
Timing Setup
Align the notches in the camshaft

so that the valves for the #1 piston

are closed.
A32mm wrench can be used to turn

the camshafts.
Special Tool T10068 is used to

position the camshafts correctly.
@ &
Timing Setup
Load the camshaft adjusters in the

direction of the arrows before

installing.
Note: After setting camshaft timing,

and before reassembling the covers,

it is a good idea to hold the chain by

hand to prevent slack while turning

the engine over a few times. This

will assure that the timing is correct.
@
Timing Setup
Align the marks on the intake and

exhaust camshaft timing adjusters

with the notches in the chain tensioner

housing.
Count 16 chain links from the arrow

on the intake timing adjuster, place

a load on the exhaust timing

adjuster, and line up the aligning

mark with the notch in the chain

tensioner housing.
(pointing at arrow)
(pointing at arrow)
@
Timing Setup
The complete timing procedure is

outlined in VESIS.

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