Why the BMW Vanos Fails! How Do I Know?

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Why the BMW Vanos Fails! How Do I Know?

Post by Shipkiller » Sat Mar 13, 2010 9:29 pm

Many persons here have asked these questions.

Below is a very good description, in layman terms so everyone should be able to understand it.
So here is a reprint of an article over on BMW-Planet. http://www.bmw-planet.com/2009/01/11/34/
I reprint this because these sites come and go, but give credit where credit is due. There is a lot of good info over on BMW-Plant.com. Hopefully it won't go away, so go over and check it out.


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 improved engine performance.

What’s wrong with my vanos?
If you own a BMW 6-cylinder single vanos car, engines M50TU, M52, US S50, S52, 1992-1999, or double vanos car, engines M52TU, M54, M56, 1998-2006. , then your vanos is experiencing a failure. These vanos units utilize 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?
Overall loss of torque and power, particularly in the lower RPM range, < 3k. Bogging then surging at 3k RPM. Uneven power distribution and RPM transition. Engine hesitations in the lower RPM range, < 3k. Louder idle and intermittent idle RPM hiccups. Difficult takeoffs. Loss of power and bogging when AC on. Increased fuel consumption.
Double vanos cars with the M52TU engine (98/99-00) experience cold weather cold start idle jolts and possible stall.

What are the benefits of repairing the vanos?
Overall increase in torque and power, particularly in the lower RPM range, < 3k. Resolution of bogging then surging at 3k RPM. Smooth even distribution of power and RPM transition. Resolution of engine hesitations in the lower RPM range, < 3k. Quiet stable idle. Smooth easy takeoffs. Improved performance when AC on. Reduced fuel consumption, by ~10%.
Resolution of double vanos M52TU engine (98/99-00) cold weather cold start idle jolts and possible stall.

How can I verify my vanos is failing?
On M52TU engine cars (98/99-00) experiencing cold weather cold start idle jolts and possible stall, 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 cars the vanos needs to be removed from the engine for inspection. Once the vanos cylinder covers are removed, an inspection of the piston seals fit in the cylinders will show a loose fit and thus a seals failure. Removal of the seals from the pistons will show the inner O-rings have flat spots and a loss of elasticity.
In general, a diagnosis is not necessary. The vanos Buna O-rings are deteriorating in 20k miles (32k kilometers). Thus essentially all the cars with these vanos units have deteriorated O-rings and a failing vanos.

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 (http://www.beisansystems.com) provides vanos seals kits that include both the upgraded O-rings and Teflon seals. Repair procedures are 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 kit, single $30, double $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.

Source: beisansystems.com
Full link: http://www.beisansystems.com/faq.html

Additionally, you can buy a re-manufactured Vanos WITH the updated O-rings from this site: http://www.drvanos.com/

Some have just blasted out a question to the board and refused to do a search of the forum first. This is a NO NO. It is a breach of forum etiquette. Just a simple Google search will reap large amount of data.
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Re: Why the BMW Vanos Fails! How Do I Know?

Post by billygilly » Tue Feb 15, 2011 2:45 am

no comments but i liked, very useful and concise
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Re: Why the BMW Vanos Fails! How Do I Know?

Post by pkerrigan21 » Mon Aug 29, 2011 1:18 pm

Hello Skipkiller,

I have been reading and reading about the vanos repair from this thread:
http://www.z4-forum.com/forum/viewtopic ... &p=406753#

I went to the dealer because I had a check engine light on, and they told me I needed a new Vanos Solenoid. They said they ran some tests and the o2 sensors originally were showing up as faulty but after resetting it a bit they found out it was the vanos solenoid on the exhaust side. - They said it would cost $500.00 installed. Would replacing the O-rings and gaskets solve this check engine light like the forum above, or do I really need to replace that solenoid. If it needs replaced is this something that I could just do along with replacing the gaskets and orings since I will be in there?

looking for your wisdom here.


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Re: Why the BMW Vanos Fails! How Do I Know?

Post by BMWZ4MC » Sat Sep 03, 2011 4:59 pm

Interesting article. There is also a known, separate problem with the VANOS bolts loosening on the pre-2007 S54 engine of early Z4Ms and the E46 M3. If these loosen, a noise will be heard that is not dissimilar to that from worn valve gear, but with a markedly more heavy bass element. Eventually the bolts will fail in themselves if the problem is not addressed, with consequences on the valve gear. If they have not failed but simply loosened, the bolts can be exchanged for modified bolts, which are tightened to a higher tourque setting.
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Re: Why the BMW Vanos Fails! How Do I Know?

Post by rokee » Wed Sep 23, 2015 8:45 am

M52 has one problem:

During normal engine operation, vibrations from pressure pulses inside the intake manifold cause the bell crank lever and flapper valve to vibrate against each other where the hex shaped portions contact each other. These vibrations start a wear process which will cause the tiny glass fibers in the flapper valve to become exposed. Once the fibers become exposed they start to erode away the male hex portion of the weaker bell crank lever. As soon as the erosion starts it's all down hill from there until the hex is completely worn away. The symptoms of a worn DISA valve include rough idle, lean engine codes and lack of low to mid rpm power.
If you disassemble a worn out DISA valve and look at the bell crank lever it's common to not even recognize that it once had a hex shape on the protrusion. Once the hex is shape is worn off the lever, the flapper valve no longer opens and closes in a controlled manner by the rotation of the bell crank lever. The brittle flapper valve becomes free to slap around uncontrolled within the DISA support framework. This uncontrolled movement can lead to complete destruction of the flapper valve. The broken pieces of valve have no where else to go except through the intake manifold runners and through the motor, sometimes resulting in severe engine damage. Even a small piece of plastic broken off the flapper valve can hold an intake valve open, resulting in bent valves or much worse.
Since the only parts on the DISA valve that typically fail are the flapper valve, bell crank lever and housing seal, why replace the entire unit. Replace the failed internal parts with these http://vanos-bmw.com/disa-bmw-repair-kits upgraded parts and have a much more reliable DISA for 1/3 the cost.

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Re: Why the BMW Vanos Fails! How Do I Know?

Post by Mike6 » Wed Sep 23, 2015 10:38 am

I posted yesterday on the DISA thread that I had removed my unit for inspection and it wasnt very dirty and the flapper moved as it should without any free movement. However at the top end where the pin goes through the housing there was a small amount of sideways movement. I cleaned it all up and put it back making a mental note to check it every now and then. But does this small amount of movement suggest it is failing. Car has covered 55000 miles.

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Why the BMW Vanos Fails! How Do I Know?

Post by M1ghty_m0use » Sun May 01, 2016 9:47 am

Just reading about the vanos solenoid

From reading this I gather that up to 2006 are most of the issues with people experiencing problems with their vanos, which I gather is due to the buna oem O ring.

Can I assume then that after 2006 BMW changed the material that the O rings were made from to dismiss this failing ?

Therefore my 57 coupe shouldn't really suffer from this vanos issue,

Even though I'm not experiencing any issues apart from only getting 20mpg city driving but that may just be me and traffic , Just wondering if it's worth looking at mine and servicing them.

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Why the BMW Vanos Fails! How Do I Know?

Post by Vanne » Sun May 01, 2016 10:40 am

Thx Shippy, great article and a good read. :D
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