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I am fairly new to BMW scene and keep noticing everybody replacing their "vanos". What is vanos? And what is involved in replacing it? Is it a "must-do"? expensive? DIY or take it to a shop? Somebody school me.....:hmm:
 

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I don't hear of too many individuals actually replacing their entire VANOS unit. It's much more common to replace the rubber seals within the unit that go bad and cause it to start making noise. Others have also reported a slight power loss when the VANOS seals are bad.

VANOS is BMWs variable valve timing system. Double VANOS monitors both intake and exhaust pulses.

In terms of repairing it, I would first try to find out if you're experiencing the typical rattling noise to begin with. After that, I would read up on the DIYs and order the Besian systems kit. Paying to have the VANOS done at a shop would be quite expensive.
 

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The vanos advances or retards the timing of the valves based on what you're doing with your foot, by moving the camshafts a little in or out.

Anyway, there's an o-ring and teflon seal on each of the two vanos pistons. Over time, the o-ring becomes stiffer and seemingly doesn't hold the seal tight within the cylinder walls. I guess with lower oil pressure from this 'leak' it fails to advance or retard as it should...not sure on the specifics beyond this 'impression.'

When doing vcg, vanos seals are maybe another 1/2-1 hour's work.
 
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