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Discussion Starter #1 (Edited)
This applies to initial cold starts only. 2-3 seconds of rattle. I only experience the rattle noise if the car is sitting for around 6-8 hours plus. Can someone explain this please? Also if the car sits that long and I turn the key for a second but not let the engine turn over (basically cycle the key) 2 or 3 times, the rattle does not happen. What’s going on here does cycling the key build up some sort of tension? Is oil pressure related?? Anyway I’m replacing it soon, just curious on how much damage the couple of seconds of rattling does on the first cold start only? And why it doesn’t do it if I cycle the key a few times? Thanks
 

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Your mechanical spring has failed more than likely but the hydraulic part is still working. Maybe it is not the tensioner but a poorly working accumulator considering the key cycle thing you tried to describe. In any event it is not the rattle you should be concerned with but the slapping of the chain you may not hear.
What destroys chain guides is the slack chain slapping against the guides, they are old brittle plastic. If you want to keep them alive changing the tensioner before it has any symptoms is the best practice. Once you break one little piece off then the rest go fast.
I would be running out today and getting a new tensioner and putting it in if it was my car.
 

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When you say 'cycle the key' do you mean you are actually cranking the engine for half a second but not long enough for the engine to start? Or are you just turning the key to run (warning lights on, fuel pump primes)? What year is the car and how many miles does it have? Do you know if it has the vanos pressure accumulator? Agree with Sailor regarding the tensioner. If it has never been replaced, I would do it now.
 

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Discussion Starter #4 (Edited)
When you say 'cycle the key' do you mean you are actually cranking the engine for half a second but not long enough for the engine to start? Or are you just turning the key to run (warning lights on, fuel pump primes)? What year is the car and how many miles does it have? Do you know if it has the vanos pressure accumulator? Agree with Sailor regarding the tensioner. If it has never been replaced, I would do it now.
Yes I mean cranking the engine but not long enough to start. Mine is a 2002 with 211k miles (she’s a trooper) not sure about the vanos pressure accumulator. The Vanos was serviced prior to my ownership.
 

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Discussion Starter #5 (Edited)
Your mechanical spring has failed more than likely but the hydraulic part is still working. Maybe it is not the tensioner but a poorly working accumulator considering the key cycle thing you tried to describe. In any event it is not the rattle you should be concerned with but the slapping of the chain you may not hear.
What destroys chain guides is the slack chain slapping against the guides, they are old brittle plastic. If you want to keep them alive changing the tensioner before it has any symptoms is the best practice. Once you break one little piece off then the rest go fast.
I would be running out today and getting a new tensioner and putting it in if it was my car.
Good advice, I’m wondering if the noise may not be the chain it’s hard to tell, like you said it maybe be a poor working accumulator. It sounds like the noise is more at the center of the engine rather then at the side. If it is slack in the chain would I still hear the noise even if I cycled the key by cranking the engine but not starting it?
 

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Sorry I don't have the time to get into all the details but if you are really hearing the chains, it is too late. You will not hear the chains until some plastic bits have been destroyed. What you are hearing has to do with slack and how that effects the valves. Once the cam lobe gets past top dead it puts the opposite load on the chain. Depending which valves are where other valves might be free to do other things. This can move the vanos piston around considering that it most likely is not full of oil yet it also could be slapping on the cover.
It is hard to say way to much to think bout even to get part way there, just replace the part and you will not have to worry about it.
 

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Discussion Starter #8
Sorry I don't have the time to get into all the details but if you are really hearing the chains, it is too late. You will not hear the chains until some plastic bits have been destroyed. What you are hearing has to do with slack and how that effects the valves. Once the cam lobe gets past top dead it puts the opposite load on the chain. Depending which valves are where other valves might be free to do other things. This can move the vanos piston around considering that it most likely is not full of oil yet it also could be slapping on the cover.
It is hard to say way to much to think bout even to get part way there, just replace the part and you will not have to worry about it.
when you say ‘if you are really hearing the chains, it’s too late’ do you mean a constant chain rattle that does not go away? I’m only hearing the rattle for 2 or 3 seconds on an initial cold start. Which I disagree with It being too late if it really is chain rattle. Based on my own research that a new tensioner has solved the cold start rattle, and when you replace a new tensioner you will get the rattle the first time you start the engine. So I’m respectfully disagreeing that it’s too late just by hearing chain rattle that isn’t constant. If I am wrong please explain. Thank you.
 

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You can disagree all you want, but then you have no way of proving it is the chain you hear rattling. If you can explain how the chain is making a noise that is a metal to metal sound when there is a piece of plastic between the metal to metal, or should I say suppose to be between them.
It is not the chain you are hearing, listen more closely with the correct tools. It is piston slap in the vanos system plus valve, lifter, and cam noise, because the system has no oil, but the cause is from the slack in the valve train.
 

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Discussion Starter #10
You can disagree all you want, but then you have no way of proving it is the chain you hear rattling. If you can explain how the chain is making a noise that is a metal to metal sound when there is a piece of plastic between the metal to metal, or should I say suppose to be between them.
It is not the chain you are hearing, listen more closely with the correct tools. It is piston slap in the vanos system plus valve, lifter, and cam noise, because the system has no oil, but the cause is from the slack in the valve train.
ok thank you, so replacing tensioner won’t help but I should anyway as a preventative. What about the noise you hear on the first engine start right after replacing the tensioner? That is not chain rattle?
 

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You still don't understand. I don't have time but I will try and explain it in simpler terms. Maybe you are missing one of the basics even though you should have read a bunch of posts on this topic and this info has been posted many a time.
The car has vanos which is variable valve timing, which means something moves. In this case it is a piston attached to a twisted gear that fits on another twisted gear on the end of the cam shaft, lets call it the vanos assembly. The cam does not move fore and aft but the vanos assembly does. Normally there is oil holding the piston in place.
The springs on the valves are very strong, the chain is working hard to push the lobe up to open the valve but the instant the valve opens past top center an opposite force is applied to the chain so now the chain has to do the exact opposite job of resisting the valve snapping shut.
If there is slack in the chain and more force resisting than pushing, the cam jumps, not really but in simple terms. The same but opposite happens at the bottom of the valve stroke. There is more than one valve and spring working, then that change in velocity moves the vanos assembly. Basically in simple terms the cam moved. This change causes the vanos assembly to move fore and aft which causes the piston to slap on the cover, that is what you hear. If you count the smacks you will find that there are way more than the rotation of the cams. That is getting too complicated so enough.
It tells me two things your Vanos boards are leaking because there should be oil in them to dampen this movement but it also says your tensioner is pretty weak, because lots have replaced the tensioner and get a vast improvement. Then some go on to do the vanos board maintenance and the problem is gone all together.
Change the tensioner to tighten up the chain so there is less slack so the cam does not slow down, or move backwards(not really but that is the slow motion effect).
Then do the Vanos boards (and maybe more) so that you don't loose all the oil when the car sits.
If this was an inline 8 or more cyl car with just two cams you would not have this problem because all the valves and springs balance the forces better. But on a V engine the chain is trying to connect the 2 banks and is doing the job of balancing the forces in the engine. So a slack chain can't balance the forces without allowing excess movement in the rotation of the cam shaft. BTW everyone of those slaps is in effect slapping the chain against the poor old brittle plastic chain guides, it is no wonder they break.
 

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Discussion Starter #12
Thank you for taking your time to break it down. You definitely made it clear and understanding. Now I just have to try and save the guides :(
 

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Discussion Starter #13
I tried to duplicate the sound today with a helper starting the car while I was standing over the hood. For this test I cycled the key but DID NOT crank the engine at all. just turned the key on and off 3x. When we started it up I couldn’t duplicate the noise. Does turning the key around do anything to the VANOS? This is getting hard to show anyone because it’s only happening on a cold start after a long standing time of 8 hours or more
 

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No matter how many tests have been done on the Accum system we don't fully understand it. If it is all working perfect we understand, but if there is a fault we don't. Nor do we know if certain faults are good or bad. "Vanos service" is not what we do with the board maintenance. In fact BMW has no service for the Vanos except replacing big chunks when faulty. Not sure what you mean by the vanos was serviced.
You are on the wrong board to have us help you justify not replacing parts or not spending money on the car, most of us promote the opposite and think new parts are always good.
 

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Discussion Starter #15
No matter how many tests have been done on the Accum system we don't fully understand it. If it is all working perfect we understand, but if there is a fault we don't. Nor do we know if certain faults are good or bad. "Vanos service" is not what we do with the board maintenance. In fact BMW has no service for the Vanos except replacing big chunks when faulty. Not sure what you mean by the vanos was serviced.
You are on the wrong board to have us help you justify not replacing parts or not spending money on the car, most of us promote the opposite and think new parts are always good.
I’m not seeking justification on not replacing parts I’m just trying to get more knowledge and understand the cars mechanics more which you have definitely helped me with and I appreciate all of your time and responses. I will be doing the tensioner and I will report back. I’m looking for a better Indy that is more familiar with these cars and can give me guidance as well.
 

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If you just cycle the key and don't crank the engine at all, that's not going to do anything for the vanos. It needs to build oil pressure, which it will do when the engine is cranking, but should already have from the accumulator. Since your car is an '02, it would have had the accumulator installed from the factory. The S54 has one too. They are pre-charged with nitrogen, so if for whatever reason that charge leaked out, it won't function as designed and reduce startup noise. You might as well start by replacing the chain tensioner and see if that makes any difference, then go from there. One thing at a time. Don't assume the worst without actually investigating.

Here's a good technical document on the S62. Pages 15-21 talks about the vanos as well as the accumulator.

 

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Discussion Starter #17
If you just cycle the key and don't crank the engine at all, that's not going to do anything for the vanos. It needs to build oil pressure, which it will do when the engine is cranking, but should already have from the accumulator. Since your car is an '02, it would have had the accumulator installed from the factory. The S54 has one too. They are pre-charged with nitrogen, so if for whatever reason that charge leaked out, it won't function as designed and reduce startup noise. You might as well start by replacing the chain tensioner and see if that makes any difference, then go from there. One thing at a time. Don't assume the worst without actually investigating.

Here's a good technical document on the S62. Pages 15-21 talks about the vanos as well as the accumulator.

good advice, I appreciate you
 

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Chain rattle will be there on idle as well. If it is only on startup after long standing then you may have vanos clatter. I would replace the tensioner first as it is cheap and preventative. If that does not help then open up the vanos solenoids and inspect the o-rings. Work your way from there.
 
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