"AT adjustment unit" ???

[tibbe]

Hi.

Had a litle rattle sound under the front of the valve cover of my -93 520IA so I lifted the cover and all seems OK, just moved the DOHC chain tensioner a bit up and down. And the sound seems to be gone. Knock knock.

Saw a unit I never seen in a car before the "AT adjustment unit" in front of the intake side camshaft. Whats that? "Adjustabe Timing"? of intake valves.

/Tibbe

[tibbe]

Found on the internet: http://www.bmwworld.com/technology/vanos.htm

It's the VANOS unit variable input camshaft timing on the M50 engines.
-------------- Qoute from web page ------------:
VANOS operates on the intake camshaft in accordance with engine speed and accelerator pedal position. At the lower end of the engine-speed scale, the intake valves are opened later ( 12.5 degrees ) , which improves idling quality and smoothness. At moderate engine speeds, the intake valves open much earlier, which boosts torque and permits exhaust gas re-circulation inside the combustion chambers, reducing fuel consumption and exhaust emissions. Finally, at high engine speeds, intake valve opening is once again delayed, so that full power can be developed.
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More info: http://www.ukcar.com/features/tech/Engine/vv/vvt_3.htm

It has variable timing, does it have a PWM or on/off control valve?.