Variable Camshaft Timing Operation

‘SYSTEM OVERVIEWS

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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

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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

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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.

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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.

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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.

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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

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Timing Setup

When servicing the 24-valve VR6,
there is a specific procedure used
to reset the timing.

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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.

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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.

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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.

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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.

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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)

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Timing Setup

The complete timing procedure is
outlined in VESIS.