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Old 11-27-2007, 07:30 PM   #9
Registered User
Join Date: Nov 2007
Location: Raleigh, NC
Posts: 1,295
My Ride: 528i 06/00
Here's the FAQ page from the Beisan website.
Also here's the link to the initial vanos diagnosis post. The "technical background synopsis" section has a lot of detailed information.

I will be glad to answer any follow-up questions.

What's a vanos?
Vanos is BMW's name for its engine variable valve timing unit.

What's variable valve timing?
Variable valve timing is a way of modifying the engine intake and/or exhaust valve opening/closing timing dynamically to provide better engine performance.

What's wrong with my vanos?
If you own a BMW 6-cylinder auto 98-06 with an M52TU, M54, M56 engine, then you have vanos part # 11-36-1-440-142 which is experiencing a failure. This vanos utilizes engine oil and pistons/cylinders to manipulate the positioning of gears to facilitate variable valve timing. The seals on the pistons are leaking due to deteriorating seal O-rings. This leakage is causing the vanos to fail in its function.

Why are the vanos piston O-rings failing?
The OEM O-rings are made from Buna, and this material is not capable of resisting the engine temperature and chemical environment. As an outcome the O-rings are hardening, shrinking, and flattening. This causes them to lose their functional characteristics causing the vanos to fail.

What are the symptoms of a failing vanos?
On autos with the M52TU engine (98/99-00) the failing vanos is causing engine idle jolts (dramatic drops) and possibly a stall on cold engine starts (< 55 F / 13 C).
On other cars with the M52TU, M54, M56 engines, car performance will be degraded. The engine will bog and hiccup at lower RPM's (< 3k). There will also be a general loss of torque and power, mostly at lower RPM's (< 3k).

How can I verify my vanos is failing?
On M52TU engine autos (98/99-00) experiencing the cold engine idle jolts, the vanos intake solenoid (metal cylinder) electrical connector can be disconnected. If the idle jolts cease then the problem is most likely the vanos.
On other autos the vanos would need to be removed for verification. Once removed the vanos can be rotated and shaken a bit and the intake piston will be heard and seen slide from one end to the other end of the vanos cylinders. This is an indication of failing piston seals, and is surely caused by the piston seal O-rings.
It has been established that the piston O-rings are deteriorating within 20k miles (32k kilometers), so essentially all the vanos units have failed.

Should I install a new vanos?
A new (rebuilt) BMW vanos costs ~$500 and unfortunately comes with the same Buna O-rings. Thus the new unit will function well at first, but the O-rings will begin to deteriorate in short order and the vanos will start failing.

Is there a good solution to the vanos problem?
To correctly address the vanos problem the piston O-rings need to be replaced with O-rings made from higher grade material. BMW has been engaged on this subject and has elected to not address the issue, "No further development will be done".
To replace the piston O-rings on a vanos requires removing the piston Teflon seals to access the underneath O-rings. Removing the Teflon seals necessarily damages them, thus both the O-rings and Teflon seals need to be replaced. Beisan Systems ( provides a vanos seals repair kit that includes both the upgraded O-rings and Teflon seals. A repair procedure is also provided for reference.

Who can I have perform this repair, and for how much?
The repair can be performed by a DIY owner with some auto repair experience. The repair is somewhat involved, but is of moderate difficulty.
Any independent BMW mechanic will be able to perform this repair. Labor time should be 4 hours. Parts include the seals repair kit, $60, a vanos gasket, $7, and two oil hose washers, $0.50.
It's prudent to change the valve cover gaskets during this repair since no added labor time is needed and the valve cover gaskets and bolt grommets cost $60.
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