6-cyl double vanos problem assessment (from Roadfly)
I'm not going to take any credit for this nor do i have any more info on the VANOS issue since i have a M62 with no VANOS but I think it's worth the read and might settle a few VANOS questions/issues.
Click here to read it on Roadfly
here's the article:
The E39 double vanos (variable valve timing unit) has a malfunction problem. This double vanos can be found on 6-cyl engines M52TU, M54, and M56, found in several model cars, E39, E46, etc, years 99-03. The malfunction symptoms are almost all subtle and mostly go unnoticed. They include lower gas mileage, lower performance, degraded emissions control, and possibly others. The M52TU engine (99-00) has one further malfunction symptom which is far from subtle. It occurs on cold weather cold engine starts and takes the form of repeated engine attempted stalls and possibly a complete engine stall. The engine rpms drop dramatically and then recover. This then repeats after a few seconds of steady idle. The problem can be more definitively diagnosed by disconnecting the vanos intake or exhaust solenoid electrical connector. If the engine stalls seize then the problem is due to the vanos. The intake solenoid electrical connector is easier to access and is located to the left (at hood) of the oil filter canister. It’s at the end of a metal cylinder (solenoid).
We (Loach & Rajaie) both own E39’s with M52TU engines. We both had the cold weather cold start engine stall symptom and were both out of warranty. We cooperatively attempted to diagnose the double vanos failure last winter (04/05). We came to the assessment that the vanos malfunction was due to deteriorating vanos piston seals. We wrote a letter to BMW/NA in May (05) presenting our findings. The letter was sent through a dealership service manager to a field service engineer who then forwarded it to BMW engineering. We received a simple response letter in July from BMW customer service. Since BMW did not seem to be taking our letter seriously we decided to present our findings publicly in October. Just before doing so, we called the BMW customer representative who wrote us the simple response letter. It turned out he was a high level individual. At that time he asked that we refrain from going public with the information and allow them the opportunity to address the problem. This was also our preferred approach. We received a simple status update in November indicating the matter was being investigated. In January (06) we pressed BMW to provide a more substantive status. We were asked to write an email indicating our concerns so that it could be passed on to others. We were told that we would be contacted in response. After two weeks from sending the requested email we sent an email requesting feed back. We received no response. We believe the high level customer service person we’ve communicated with is sincere in wanting to address the problem but that others are making the final decision. We had been told from the beginning that BMW was quite impressed with our assessment. A high level individual had also contacted the dealership service manager, whom we sent the first letter through, enquire into our interests.
We have given up on attempting to work out a solution with BMW and have decided to go forward and present our findings.
Here we present our written correspondences with BMW, and some support information to facilitate a fuller understanding of the subject issue.
Technical background references:
How an engine works:
How a camshaft and variable timing work:
How BMW’s double vanos (variable timing) works:
How EGR (Exhaust Gas Recirculation) works:
Technical background synopsis:
In this discussion it is useful to reference the following portrait of a BMW i6 double vanos engine, http://www.bmwworld.com/pics/engine/2713_832.jpg, and the double vanos pictures at the end of this document.
The crankshaft and camshaft(s) are connected via a timing belt/chain(s) which synchronizes the timing of the opening/closing of the intake and exhaust valves with the piston cycle/position. E39’s have double overhead camshafts, meaning separate intake and exhaust camshafts found at the top of the engine (head). BMW implements a time shift scheme for variable valve timing. That is, the relative rotational position of the camshaft(s) to the crankshaft is modified (shifted). This is done dynamically by command from the engine computer (DME). The scheme is achieved mechanically through the use of helical (slanted) gears. The timing chain sprocket(s) of the camshaft(s) does not connect directly to the camshaft, but has an inner hole larger than the camshaft end. There are opposing direction helical gears at the sprocket inner hole and the camshaft end. An independent splined shaft (cup) inserts between the sprocket hole and camshaft end and connects the two components. The splined shaft (cup) inner and outer surfaces have helical gears with opposing directions which correspond and mate to the sprocket hole and camshaft end helical gears. The insertion/extraction (in/out) of the splined shaft causes the relative rotational position of the sprocket to the camshaft end to change. This implicitly causes rotational position change (time shift) between the camshaft and crankshaft (connected to the camshaft sprocket via chain). An insertion of the splined shaft causes the camshaft to rotate proportionally forward causing a timing advance (earlier). An extraction of the splined shaft causes the camshaft to rotate proportionally backward causing a timing retard (later). The vanos is a devise that attaches to the front of the engine at the camshaft end, sprocket, and splined shaft. Controlled by the DME (electrical), it utilizes engine oil/pressure to manipulate the position of the splined shaft (valve timing). The vanos incorporates a piston which is bolted to the end of the splined shaft. The piston sits inside a cylinder. There are cylinder/piston enclosed oil chambers at the fore and aft of the piston. A vanos valve controls the flow of pressurized engine oil into the two opposing chambers. The valve position is manipulated by a solenoid which is controlled electrically by the DME. The DME controls the oil pressure in the opposing cylinder/piston oil chambers to position the piston, and thus control the valve timing. The DME receives piston / splined shaft / camshaft position feedback from the camshaft position sensor. Both intake and exhaust sides incorporate the same configuration scheme and the DME controls both independently.
The traditional structural scheme for implementing EGR (exhaust gas recirculation) is to circulate exhaust manifold gases back into the intake manifold. This method can be termed “external” EGR. The E39 i6 with double vanos does not implement an external EGR scheme. Due to the time shift abilities of the vanos, valve timing can be manipulated to allow for exhaust gases to remain in the cylinder after combustion and be mixed in with the next cycle intake air/fuel mixture. This scheme is referred to as “internal” EGR. It’s an efficient scheme, but is highly reliant on the proper function of the vanos for effective variable valve timing.
Letter sent to BMW/NA through local dealership:
May 9, 2005
[address and contact info]
(Loach) xxx xxx
[address and contact info]
Service Manager, xxx BMW, Inc.
[NC address and contact info]
Dear Mr. xxx (service manager):
BMW autos with the M52TU engine have been experiencing a cold weather related problem for the past few years. The problem has been dubbed the “vanos problem”. We both have (had) this problem and are out of warranty. We’ve taken the initiative to isolate the problem cause and seem to have identified the culprit. Below is an explanation of the problem and our findings.
The problem occurs on M52TU engine cars, 3 & 5 series 6-cylinder 1999-2000. It presents when the car is cold, ~ < 55° Fahrenheit, usually in the morning. The problem begins at the end of the warm-up period (elevated idle rpm). Thus the colder the car, the more delay after startup before the problem manifests. At the end of the warm-up period the engine begins a series of stall encounters. The engine rpm’s drop significantly, the engine shudders, and then the engine rpm’s recover. This engine jolt lasts ~1 second. It is followed by a steady idle for ~7 seconds. The cycle then repeats. This continues for ~4.25 minutes. The 7 second idle interval can also be shorter, even to a ~1 second interval. With some cars the engine will actually stall on one of the engine jolts. If the car is driven before/during the episode, the problem seems to be suppressed, unless the car shortly comes to an idle state where the problem reappears. If the hood is opened, a gear/chain like chatter can be heard during the stall encounters. The idle control valve can sometimes also be heard clunk open.
The M54 and M56 engines share the same vanos as the M52TU engine, but don’t exhibit the “vanos problem”.
At first we thought the problem was due to the idle control valve. But cleaning the ICV and then replacing it with a new unit did not resolve the problem. We then learned that the problem was vanos related. We realized that the problem takes place when the DME adjusts the variable timing at the end of the warm-up period. We received a tip from a BMW head mechanic that the problem was due to tight tolerances on the helical gears and that BMW was redesigning the splined shaft to solve the problem. Given that BMW has redesigned the splined shaft several times, we replaced the two splined shafts with the latest design splined shaft. There was no improvement. We received another tip that the problem was due to the vanos valves. We replaced the valve on the vanos exhaust side, and found no change. We tested the solenoids, and found them to work properly. We then decided to acquire a new vanos. We compared the new vanos with a vanos that had the vanos problem, and found them to be virtually identical. We did notice though that the piston seals on the new vanos protruded out further than in the used vanos. This we surmised was due to wear on the used vanos seals. We suspected the vanos problem was caused by a fault on the vanos exhaust side. There is a powerful spring at the vanos exhaust side which fully advances the vanos exhaust piston in the default/off state. We expect this design facilitates advanced exhaust valve timing when the engine is first started. To retract the exhaust piston (retard timing) would need significant oil pressure to counter the powerful opposing spring. Our conclusion was/is the worn leaking seals prevent the oil pressure build up needed to reposition the piston. We replaced both pistons on a used vanos with the pistons from the new vanos. The “vanos problem” resolved! We were also quite pleased to find that the car performance noticeably improved. The engine rpm’s were smoother/cleaner throughout the higher rpm range; this we know is the hallmark of the double vanos. Given the performance enhancements, we concluded that the vanos fault not only caused the cold morning symptoms, “vanos problem”, but also afflicted the function of the vanos during normal operating temperatures. This would not only affect driving performance, but would also afflict the function of the EGR (exhaust gas recirculation), which is highly reliant on the proper function of the vanos. EGR plays an important role in fuel consumption and emissions control.
It seems evident that the vanos malfunction is due to worn piston seals.
The M54 and M56 engine autos utilize the same vanos as the M52TU but do not encounter the “vanos problem” (cold morning stall cycles). These engines have equivalent oil pressure characteristics to the M52TU, and thus are not more able to overcome the seal leak and build the needed pressure. We thus expect that the M54 and M56 engine autos are also encountering vanos malfunctions due to worn piston seals.
We suspect the M52TU cold engine “vanos problem” is related to the M52TU DME. The DME is likely not receiving the anticipated indication from the camshaft position sensor, and reacting in a way that causes the engine to almost stall. The DME could be over opening the ICV causing the engine to almost stall. This can also explain the ICV clunk that is sometimes heard during the engine attempted stall. We expect that the M54 and M56 DMEs function differently and thus do not instigate the cold engine stalls.
Upon further inspection of the vanos piston seals, we’ve found that each seal is not one component but a set of two rings. There is an outer Teflon seal ring, and an inner (supporting) elastomer o-ring. We believe it is the inner elastomer o-ring that wears and shrinks, causing the outer Teflon seal ring to retract, and thus creating the leak condition.
BMW does not provide the vanos pistons or piston seals as a separate part. A new (remanufactured) vanos needs to be purchased to acquire the piston seals. A new vanos costs ~$500. A BMW dealership vanos replacement repair is ~$1,000.
Some owners have had their vanos replaced one winter only to have the “vanos problem” recur the next winter.
The “vanos problem” is practically an epidemic. There are numerous M52TU owners with this ailment. It’s also evident that a routine replacement of the 6-cylinder double vanos piston seals is necessary for the proper function of the vanos.
We would like to see BMW be more forthcoming with information on this issue. We also would like to see BMW provide the piston seals as a separate part. This would significantly reduce the part costs of the repair. Redesigning the seals so they may have a longer functional lifespan would be a greatly welcomed solution.
As can be expected, we feel compelled to share our findings publicly. We are open to the possibility of doing this in coordination with BMW.
Your response will be greatly appreciated. Rajaie xxx will act as the primary contact. Thank you for your assistance.
Rajaie xxx & (Loach) xxx xxx
Letter received from BMW/NA:
July 6, 2005
Mr. Rajaie xxx
Re: 2000 528i
Dear Mr. xxx (Rajaie):
I have your communication dated May 9th, and wish to apologize for not contacting you sooner.
In response, we are currently reviewing the subject issue which you have presented, and will respond in more detail when additional information is available. Thank you for your patience in the interim.
Relations & Service
Email to BMW/NA
Date: Oct 26, 05
Subject: 6-cyl double vanos problem assessment
Hello xxx (customer rep),
It was a pleasure speaking with you today. I'm glad that you are willing to further consider our assessment of the double vanos malfunction. We hope BMW's engineering teem can find a long term solution for the problem. Again this is our primary interest. The last section of our original letter states clearly or requests of BMW.
Below is a document that we have recently composed to post on the Roadfly forum. It has our letter correspondences and further supportive information.
I'll look forward to your response and hope we can find a solution that will best serve BMW and its automobile owners.
xxxxxxxxxxxxxxxxxxxxxxxxxxxx (documentation very similar to this document)
Email to BMW/NA
Date: Oct 27, 05
Subject: Roadfly post on vanos problem
Hi xxx (customer rep),
Just wanted to show you an example post from yesterday on the vanos problem. We’ll be seeing these several times a week from now through the winter.
Be sure to read the follow up threads.
Email from BMW/NA
Date: Nov 10, 05
Subject: RE: 6-cyl double vanos problem assessment
Good morning Gentlemen:
As a follow-up to your communication and our telephone conversation, I'd like to thank you and Mr. xxx (Loach) for your double vanos assessment. We are still reviewing and testing and exploring some of our own theories. It may take some time before our study is concluded. We will get back with a response and wish to thank you for your patience in the interim.
xxx xxx (same customer rep)
Email from BMW/NA
Date: Dec 29, 05
Good morning Mr. xxx (Rajaie):
As a follow-up to your voice mail message of December 27th, please be advised the matter is still be reviewed and there is nothing further to be added to my early November response at this time.
National Customer Relations
Email to BMW/NA
Date: Jan 9, 06
Subject: Vanos resolution status
Hello xxx (customer rep),
In our recent phone conversation you asked me to write you an email noting mine and xxx’s (Loach) concern regarding the vanos matter with BMW.
As you know we investigated the double vanos failure last winter and assessed the failure was due to the piston seals and likely the inner supporting elastomer seal. We presented a letter to BMW in May with our findings and asked that BMW address the matter. We received a letter in July indicating the issue would be looked into and that we would be contacted. We called BMW in November [mistake, should be Oct] and found that nothing had transpired regarding the matter. We were told at that time that the issue would be taken seriously and addressed. The most recent status we’ve received is essentially that “BMW is looking into the matter”, with no supporting information for the status or an indication of a timeframe for a solution.
The double vanos in question is a component of i6 engines in model years 99-03. Vanoses on these engines have been failing and getting replaced for over 4 years now, at least from our anecdotal findings. We expect BMW has been aware of the problem from some period before that. There is no indication that BMW has attempted to address this problem. Newer vanoses have continued to fail in the same manner and in as short a period as 1 year. BMW hasn’t even officially acknowledged that a problem exists. Given this history we are reluctant to accept BMW’s current status of “the matter is being looked into” without any supporting information or timeline.
We would like to know that a scheduled project is under way; that viable seal products have been chosen; that tests are being conducted on test beds; and that a timeframe is expected for the findings to be collected and assessed. We would like to see that in case a significant seal lifespan improvement is not feasible that the seals be provided as a separate component. A vanos repair is ~$500 parts and ~$500 labor. Seal costs are in the few dollar range, and having them as a separate component would half the repair costs.
A vanos failure has significant implications to engine function. Performance will degrade; gas consumption will degrade; emissions control will degrade, particularly with the EGR NOx control becoming dysfunctional. Also M52TU engines will suffer from cold weather cold car engine rpm oscillations and stalls. These are not insignificant engine function failures.
We believe it is in the best interest of BMW and BMW automobile owners that this problem be addressed and a viable solution found. We would hope that BMW can see the significance of this issue and address it with priority. But given the history of this case it would be remiss on our part to believe that an indication of “the matter is being looked into” is a sign of such an effort from BMW.
Thank you for your consideration of this matter and our concerns.
xxx xxx (Loach)
Email to BMW/NA
Date: Jan 23, 06
Subject: RE: Vanos resolution status
Hello xxx (customer rep),
Any response to this email?
You can reach me on my mobile, xxx.
The proper function of the internal EGR is highly reliant on the proper function of the vanos. If the vanos is malfunctioning then it’s likely the vehicle is not performing EGR within EPA requirements.
- No fault codes
It is intuitive to ask: If the vanos is malfunctioning, then why is the DME not setting a fault code and turning on the Service Light? The DME must be aware of the failure from the CPS (camshaft position sensor). From the performance enhancement attained after replacing the vanos pistons (seals), we know the variable valve timing was not working well. Even more egregious, the EGR is also likely failing, and denoting this failure is probably an EPA emissions standard requirement.
- Catalytic converters placed closer to engine
It is advantageous to mount catalytic converters close to the engine so they can warm up quickly on cold starts. But this is not usually done since exhaust temperatures can reach extremely high levels which will damage catalytic converters. Thus in most automobiles, including BMW, the converts are usually placed further down the exhaust under the car. With BMW double vanos cars the catalytic converters are place on the exhaust manifold, very close to the engine. We expect this is facilitated by the exceptional functionality of the vanos EGR, insuring peak combustion temperatures are contained to safe catalytic converter levels. If the vanos EGR is not functioning well then the catalytic converters could be at jeopardy of over heating and experiencing a shorter lifespan.
- Vanos problem on cold weather cold start
The letter to BMW explains that the M52TU engine exhibits the vanos problem only on cold weather cold starts, but it doesn’t explain why. Vanos variable timing facilitates multiple features and benefits, including minimizing nitrogen oxides, re-combusting unburned fuel for better gas mileage, better performance, etc. Another benefit is the ability to lower unburned fuel emissions and quickly heat up the catalytic converters on cold starts. At initial engine start, the exhaust valve timing is fully advanced (early) and the intake valve timing is fully retarded (late). This minimizes valve opening overlap, thus insuring a minimally contaminated intake air/fuel mix for optimal combustion on cold starts. At the end of the engine warm up period (elevated idle rpm) the valve timing is adjusted. This facilitates a lower air/fuel mixture and lower hydrocarbon emissions that the cats are not capable of processing in their current cold state. Timing adjustments are also utilized to bring the cats to operating temperature faster. Thus it is at this stage of the cold startup cycle when the valve timing is being adjusted that M52TU engines encounter the “vanos problem”.
- Seal replacement consideration
It’s quite intuitive to consider replacing the vanos piston seals as a solution to the vanos malfunction. The problem is also likely resolved by just replacing the inner supporting seals. These inner seals should also be easier to acquire than the Teflon outer seals.
Unfortunately this solution is more complicated than is initially perceived.
The vanos first needs to be removed from the car. This involves removing the fan/shroud, crankcase valve cover, then unbolting the vanos from the splined shafts and engine head. The vanos cylinder covers can then be removed and the pistons extracted.
It is not simple to remove the outer Teflon seals without damaging them. They are recessed into the piston seal grooves and need to be pried out. They are easily nicked and when stretched do not fully retract. Due to these complications it might not be feasible to reuse the outer Teflon seals.
The inner seals are quite elastic and are easily removed from the piston. New ones could also be easily installed. These inner seals seem to be made form a form of Buna (synthetic rubber, Ex Nitrile). We have attempted to replace them with similar size O-rings and have found the Standard (SAE) O-ring thickness to be a close fit. It’s difficult to know the exact original sizes (inside/outside diameter and thickness) of the inner seals. The used seals outer and inner surfaces have flattened and their overall thickness has likely shrunk.
An effective method for finding a replacement for the inner seals might be to first purchase a new (rebuilt) vanos to acquire a new set of inner seals, then to solicit professional advice for assessing the composition of the seals and locating an equivalent replacement. The same could be done for the outer Teflon seals, although it would likely be more difficult to locate an equivalent.
If equivalent replacements for the seals were located and installation was feasible, it would still be difficult to fully assess the efficacy of their use.
Double vanos pictures:
Double vanos with splined shafts (cups) attached to pistons. Exhaust on left, intake on right. Note exhaust splined shaft is advanced (inserted) by default.
Double vanos. Note advanced exhaust piston. Intake piston can move freely, but exhaust piston can only be retarded by powerful force.
Double vanos with cylinder/piston covers removed. Spring behind exhaust piston fully advances piston by default. Two sets of seals on each piston facilitate dual oil compression chambers to control advancement (out) and retardation (in) of the pistons. Oil passage access at bottom of piston cylinder, and through cylinder cover, facilitate oil pressure control in two oil chambers.
Two pistons, right with seals installed, left with seals removed. Each seal set is made of two rings. The outer (left) is a Teflon seal and the inner (right) is an elastomer O-ring. Vanos exhaust and intake pistons and seals are same part components.
528i 5sp 06/00